Journal of Southwest Petroleum University(Science & Technology Edition)

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Fault Block Types and Their Fault Seals in the Southern Slope of the Dongying Depression

YANG Huaiyu

西南石油大学学报(自然科学版) 2020, 42 (1): 1-9. DOI: 10.11885/j.issn.1674-5086.2018.09.17.02

Abstract （187）

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There are numerous fault traps formed by consequent and antithetic faults in the Shahejie Formation of the southern slope of the Dongying Depression. The tectonics of these fault traps is favorable for reservoir formation but only part of the fault traps were formed into reservoir. Therefore, the geological properties of these faults restrict the effectiveness of their seal for oil and gas. This study examines various fault properties, such as activity, displacement, sandstone thickness to total formation thickness ratio, cross-sectional stress, interstitial fault tolerance, and shale gouge ratio to investigate the seal of the three main fault block types in the study area, namely consequent, antithetic, and composite consequent-antithetic fault blocks. The results demonstrated that the antithetic fault blocks of the systems with high sand content (Member 2 of the Shahejie Formation) is favorable for reservoir formation whereas reservoirs are less likely to form in the consequent fault blocks. Reservoirs can form in both the consequent fault blocks and the antithetic fault blocks of systems with medium and low sand content (Lower Member 4 of the Shahejie Formation and Kongdian Formation). In particular, formation in the antithetic fault blocks is more common. In addition, research on conjugate composite fault blocks with opposite dip directions shows that the seal of the oblique composite fault blocks is better than that of their collinear counterparts. The master and auxiliary faults with oblique composite fault blocks fulfill the empirical fault seal parameters and the corresponding collinear composite fault blocks is also favorable for reservoir formation.

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Reservoir Formation Patterns in the Strike-slip Fault Zone of the Halahatang Oilfield

ZHANG Yintao, SUN Chong, WANG Xuan, YUAN Jingyi, YIN Huairun

西南石油大学学报(自然科学版) 2020, 42 (1): 10-18. DOI: 10.11885/j.issn.1674-5086.2018.08.20.02

Abstract （181）

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Massive strike-slip fault zones are key factors for reservoir formation in the Ordovician fractured-vuggy carbonates. The Halahatang Oilfield is on the western slope of the Tabei Uplift. The fault displacement of the strike-slip faults in this region is relatively small. As a result, it is difficult to identify these faults and thus the exploration and exploitation of the oil field is restricted. This study utilized the evolutionary characteristics of the strike-slip faults in the oilfield and formulated a multiplefiltering-based research method for explanatory processing of seismic data. This was applied to the detailer depiction the strikeslip fault zone in detail and determine the spatial distribution pattern of the faults to investigate the reservoir control mechanism of the strike-slip fault zone. It was found that the strike-slip fault zone enables oil and gas to flow. A descriptive technique for fault-karst carbonate reservoirs based on the fault zone was then developed and a formation model for the fault-karst carbonate reservoirs in the Halahatang Oilfield was established. It was concluded that each of these fault-carbonate reservoirs was formed in one single carbonate system and they were interconnected in a complicated manner. Through detailed carving of fracturedvuggy systems and prediction of fractures after superimposition, an evaluation method is proposed to measure the potential of the fault-karst carbonate reservoirs in the Halahatang Oilfield.

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Control of the Syndepositional Fault on Depositional Fillings of the Dongying Formation in Northern Liaodong Bay

XIA Shiqiang, LIN Changsong, DU Xiaofeng, LI Junqian, LI Hong

西南石油大学学报(自然科学版) 2020, 42 (1): 19-32. DOI: 10.11885/j.issn.1674-5086.2018.07.18.02

Abstract （217）

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To investigate the control of the syndepositional faults on the depositional fillings in the lower E d ₂, regional core analysis data, drilling logs, and seismic data from the northern section of the Liaodong Bay Depression were used to analyze sequence division, changes in activity level of synsedimentary faults, and controlling effect on the axial meandering river deltasublacustrine fan sedimentary filling evolution in the lower E d ₂ segment layer. The lower E d ₂ segment layer was shown to be comprised of three layers that can be divided into lowstand+transgressive system tracts and highstand systems tracts according to the flooding surface. In the lower+transgressive system tracts, the meandering river delta developed in the high sedimentation rate stage due to syndepositional fault activity. The difference in stratum thickness between the two sides of the fault was significant, and the turbidity formed by the slump showed strong amplitude, low frequency, and high continuity on seismic section. According to the drill logging calibration, the logging curve exhibited a tooth shape with medium to high amplitude and the lithology was mainly siltstone and mudstone without obvious depositional structure. The meandering river delta in the highstand systems tracts formed in the low sedimentation rate stage due to syndepositional fault activity. The difference in the stratum thickness between the two sides of the fault was negligible, and the turbidity formed by the slump was characterized by a vermicule chaotic reflection with weak amplitude on seismic section. The logging curve exhibited bell or funnel shapes of medium to low amplitude and the lithology was predominantly medium coarse sandstone with gravel present in local areas. In addition, the depositional structure was shown to be dominated by soft-sediment deformation structure.

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Sedimentary Characteristics of Nearshore Subaqueous Fans in the Heilongmiao Area of the Nanyang Sag

WU Qun, YANG Yunfei, WANG Shufang

西南石油大学学报(自然科学版) 2020, 42 (1): 33-44. DOI: 10.11885/j.issn.1674-5086.2018.09.10.02

Abstract （236）

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To determine the sedimentary characteristics and spatial evolution of nearshore subaqueous fans in the Heilongmiao Area, core observation, logging, laboratory analysis, and high-precision 3D seismic data analyses were performed. The lithology of the study area was mainly comprised of glutenite, gravel sandstone, pebbly sandstone, and fine sandstone, with major sediment pore types of intra-grain dissolved pores and intercrystalline pores. Gravity flow deposition structures were reflected by the blocky bedding, flushing surface, torn fragments of dark mudstone, liquefied structures, and sedimentary structures formed by traction flow, and we also found deposition structures of small-scale cross-bedding, horizontal bedding, and slab-like crossbedding. The sediments were divided into subphases of fan roots, fan body, and fan-end. Among them, the braided channel in the fan body exhibited the best physical properties and provided good reservoir conditions for oil and gas accumulation. The second section of the Hetaoyuan Formation in the Heilongmiao Area was divided into three subsegments. The development of the fans in each subsegment was controlled by the datum level change, and the overall sedimentary evolution model showed a superimposed fan development of progradation and regression.

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Characteristics and Significance of Carbonate Cement in the No. 7 Area of Lenghu, Northern Margin of Qaidam Basin

WANG Yetong, SUN Guoqiang, YANG Yongheng, QIN Caihong, LI Yanming

西南石油大学学报(自然科学版) 2020, 42 (1): 45-56. DOI: 10.11885/j.issn.1674-5086.2018.09.12.01

Abstract （151）

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Carbonate cement is the most common type of cement in clastic reservoirs, and its formation environment, material source and diagenetic temperature are of great significance to the reservoir research. Through the analysis of petrology, mineralogy and geochemical of the sandstone carbonate cementation in the Xiaganchaigou Formation of Lenghu No.7 in the northern margin of Qaidam Basin, this paper shows that there are four types of sandstone carbonate cements in the Xiaganchaigou Formation in the study area which are calcite, iron-bearing calcite, iron calcite and dolomite respectively. The content of carbon isotopes (δ ¹³C _PDB) and oxygen isotopes (δ ¹⁸O _PDB) are 8.81‰~3.51‰ and 8.77‰~17.36‰ respectively, with averages value of 5.33‰ and 13.50‰, respectively. Paleosalinity and temperature are 113.61~102.85 and 63.03~123.06℃ according to carbon isotopes and oxygen isotopes calculation, the average value is 109.66 and 94.47℃, respectively. It reflects that the diagenetic stage of the Xiaganchaigou Formation is from early diagenetic stage B to middle diagenetic stage A, whose formation process is influenced by the decarboxylation of organic matter. The diagenetic environment is acidic, and the diagenetic fluids mainly come from the precipitated water of the clastic and the leaching fresh water in the atmosphere. Besides the influence of diagenetic environment and temperature, the physical property of reservoir has a significant negative correlation with the carbonate cement content. And with the increase of carbonate cement content, the porosity and permeability of the reservoir decrease.

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Fractal Characteristics of Coal Rock Pores in the Baliancheng Mining Area, Hunchun Basin

WANG Youzhi

西南石油大学学报(自然科学版) 2020, 42 (1): 57-68. DOI: 10.11885/j.issn.1674-5086.2018.10.10.03

Abstract （174）

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Pore structure characteristics of coal rocks are important parameters for evaluating coal seam storage capacity and selecting fracturing layers. Low temperature nitrogen adsorption, nuclear magnetic resonance (NMR) technology, and argon ion polishing imaging enabled quantitative characterization of the pore heterogeneity by fractal theory were used to examine the influencing factors of fractal dimensions. The organic pores of the coal rocks from the Baliancheng mining area comprised mainly of plant tissue, intergranular, and gas pores, whereas the mineral pores were composed of dissolution and clay mineral pores. The type I curve indicated that the coal rock developed slit-like and wedge-shaped holes, while the type II curve indicated the development of bottle-shaped pores. The NMR bimodal T ₂ spectrum showed that the adsorption pores were developed only to a limited degree with poor connectivity. The trimodality indicated the development of weep holes and fissures under good pore percolation conditions. When the pore diameter ranged between 2 and 100 nm, the water content and specific surface area were positively correlated with D ₁, whereas D ₂ was positively correlated with the ash content and negatively correlated with average pore size. When the pore diameter was between 0.1 and 10.0 μm, D _N1 obtained by NMR was positively correlated with the surface area of the pores and D _N2 was positively correlated with the volume of the percolation pores. In addition, D _M and the fractal dimension D _c of the dissolution pores were largely controlled by the clay mineral and feldspar contents, respectively. Therefore, coal layers exhibiting a nitrogen adsorption type I curve and trimodal nuclear magnetic T ₂ map are conducive to the development of coalbed methane.

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Seismic Reflection Anomaly Identification and Origin Analysis of A Oilfield in Iraq

LIU Junhai, XU Minghua, WANG Ziming, HAN Cong, WANG Haifeng

西南石油大学学报(自然科学版) 2020, 42 (1): 69-77. DOI: 10.11885/j.issn.1674-5086.2018.09.10.03

Abstract （204）

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In Oilfield A there are many seismic reflection anomalies which is concave or broken seismic event. At present, there is a lack of in-depth research and clear understanding of identification and origin of seismic anomalies, which has affected the oil and gas exploration process. Coherence, variance and likelihood seismic attributes are used to identify seismic reflection anomaly. The results indicate seismic anomaly extends shortly laterally but extends from dozens of meters to a kilometer vertically, and they are of subcircular shape in plan view, most of which are irregular distribution and few of which is linear or echelon distribution. A comprehensive analysis of the origin of seismic anomaly is made based on structural evolution, stress and core data of target formation. The results indicate that seismic reflection anomalies are the combined result of dissolution and compression. Dissolution develops in target formation but development intensity is uneven horizontally and vertically. Because late compression is weak, fault is generated in fragile area of target formation. Some seismic anomalies are the vertical path of oil migration and some seismic anomalies destroy trap of lower formation.

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An Experimental Study on Improving the Liquid-carrying Capacity of Wellbore Gas by a Multi-stage Orifice

WANG Qiwei

西南石油大学学报(自然科学版) 2020, 42 (1): 78-83. DOI: 10.11885/j.issn.1674-5086.2018.07.24.01

Abstract （147）

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Liquid accumulation in the bottom hole of gas wells will affect the production process and lead to production stoppage in severe cases. Measures currently taken to drain bottom liquid include the adding of foaming agent, replacement of smalldiameter tubing, and nitrogen lift. These measures are play an important role in gas well production, but the wellbore structure that causes liquid backflow has not changed. Changing the conventional wellbore structure to suit for single-phase fluids could help reduce the backflow of liquid in a wellbore of gas-liquid two-phase flow and improve the liquid-carrying capacity. We propose a wellbore structure suitable for gas-liquid two-phase flow that has practical significance for improving gas well production. We design a multi-stage orifice device similar to the inverted funnel that is installed in the wellbore tube. Bottom hole gas is used as the kinetic energy. The orifice plate is designed to reduce or prevent liquid backflow so that the liquid passes through the multi-stage orifice plate and rises sequentially. A gas compressor is used to provide a gas source, and the effect of the addition of the orifice on the gas and foam carrying capacity at different gas flow rates is tested. When the multi-stage orifice device is added into the tube, it greatly improves the gas carrying capacity and the liquid discharging effect of the tube. It also reduces the liquid backflow and the critical value of the gas flow rate in the gas and foam drainage. The experiment proves that the method and principle of multi-stage orifice plate for gas well stimulation works well, improving the gas carrying capacity and the liquid-carrying effect of the foam as well as reducing the amount of foaming agent and residual liquid in the bottom hole.

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Prediction and Application of the Shaft Friction Coefficient Based on Drill-string Dynamics

SONG Wei, HU Zhongzhi, ZHOU Yan, SHEN Yuanyuan, WEI Na

西南石油大学学报(自然科学版) 2020, 42 (1): 84-90. DOI: 10.11885/j.issn.1674-5086.2018.07.19.04

Abstract （176）

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Accurate prediction and control of friction torque during the design and construction of drilling phases can prevent drilling accidents, and the shaft friction coefficient is a key factor in predicting friction torque. Therefore, we predicted the friction coefficients for the casing and open-hole sections for highly-deviated well drilling based on a calculation model for friction torque. This was based on drill-string dynamics and data from a near-bit, multi-parameter measuring instrument. The results were successfully applied to the analysis and control of friction torque in the third-spud drilling stage of adjacent wells of the same type. The field application results revealed that the friction coefficient of the actual drill casing was 0.27~0.29, and the friction coefficient of the open hole was 0.39~0.41, both of which are higher than the empirical values. The error between the predicted and actual values of the hook load and the torque of the case satisfied the construction accuracy requirements. The friction torque during actual drilling was monitored in real time to detect abnormal changes based on the friction torque prediction chart, which ensured smooth construction of the well. The results provide a scientific basis for optimizing drilling equipment and the well profile of highly deviated wells, and for planning the on-site drilling construction.

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Physical Simulation of Cold Recovery of Edge Water Heavy Oil Reservoir After Steam Stimulation

WANG Yanwei, LIU Huiqing, DONG Xiaohu, ZHANG Qichen

西南石油大学学报(自然科学版) 2020, 42 (1): 91-100. DOI: 10.11885/j.issn.1674-5086.2019.04.15.01

Abstract （173）

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Aiming at limited effect of thermal recovery of the edge water heavy oil reservoir with, the development method of cold recovery after steam stimulation is put forward. The physical simulation experiment of heavy oil reservoir with edge water is carried out by using the high temperature and high pressure three-dimensional physical simulation system. The temperature field of the steam stimulation process under the influence of the edge water and the production dynamic characteristics before and after the chemical cold recovery are studied. The results show that in the process of steam huff and puff development of heavy oil reservoir with edge-water, the heating range of oil layer is asymmetric due to the influence of edge-water intrusion. With the increase of steam stimulation cycle, the heating range of the oil layer near the edge water is obviously shrinking, and the water channel is gradually formed, which makes the oil layer in the vicinity of the water intrusion area deteriorate. There is a mutual influence and restriction between the heating range of oil layer and the intrusion of edge-water. Viscosity reducer plays the role of emulsifying, reducing viscosity and weakening water invasion. Combined with the law of water penetration and rational utilization of edge-water energy, the recovery rate can be increased by 34% by transforming steam stimulation into cold production. At the same time, the range of reservoir suitable for this technique is determined by numerical simulation. The results of this study can be used for reference in the development of heavy oil reservoirs with edge water.

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Percolation Resistance Characteristics of Water Drive in Offshore Light Oil Reservoirs

CHEN Xiaoming, LIU Yingxian, WU Qiongyuan, LIU Chao, ZHAO Hanqing

西南石油大学学报(自然科学版) 2020, 42 (1): 101-110. DOI: 10.11885/j.issn.1674-5086.2019.02.27.02

Abstract （192）

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In the water injection wells of light oil reservoirs, the wellhead pressure is constantly rising. Conventional measures such as acidification and microfracture cannot effectively reduce wellhead pressure. To explore the causes of injection pressure increases further, the law of variation in percolation resistance among wells is studied based on the flow tube and the principle of hydropower similarity. An expression of percolation resistance is derived by applying Darcy's Law. Percolation resistance is related to the shape of the reservoir and the total fluidity. The total fluidity change of the non-piston displacement process is usually divided into two types:monotonous increase (medium and high viscosity) and initial reduction followed by a slight increase (low stickiness). When the viscosity of crude oil is low, the total fluidity decreases, and the percolation resistance increases, resulting in increased injection pressure. In such circumstances, the wellhead pressure of the water injection well is increasing, and "pseudo-blocking" occurs, which substantially restricts the water injection. Through calculating the percolation resistance between injection and production wells in different oilfields of the southern Bohai Sea, a graph of the dimensionless resistance coefficient that reflects the law of variation in percolation resistance is obtained. The graph depicts the possible waterbearing stage of pseudo-blocking, which can effectively guide the management of the injection well. Combining this analysis with the treatment practice of the KL oilfield group, the following measures can be taken when pseudo-blocking occurs in the injection well:(1) Increase pressure and water injection for high fracture pressure and low fracture reservoirs. (2) Control the profile and oil displacement for low fracture pressure and high fracture reservoirs. (3) Develop gas drive systems for ultra-low crude oil viscosity and deeply buried reservoirs. (4) Give the vertical water drive contradiction priority for multilayer comingled mining development reservoirs.

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A New Classification Method for Offshore Low Permeability Gas Reservoir Based on Comprehensive Evaluation Parameters

YUAN Binglong, YE Qing, ZHANG Lianzhi, CHEN Zhihe, LEI Mingzhu

西南石油大学学报(自然科学版) 2020, 42 (1): 111-118. DOI: 10.11885/j.issn.1674-5086.2019.03.05.02

Abstract （202）

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The proved reserves of offshore low permeability natural gas resources increase every year, in order to economical and efficient exploit this part of the reserves, reasonable classification is essential. Target is gas reservoirs in Huangliu Formation of the Dongfang area in Yinggehai Basin, propose six parameters classification method to evaluate offshore low permeability gas reservoir, such as open-flow potential per meter, permeability, the radius of main flow throat, movable fluid saturation, gas saturation and gas reservoir thickness. Thus, a comprehensive evaluation method for low permeability reservoirs is proposed. Considering the current offshore gas reservoir development characteristics, the correlation between the various classification parameters, the low permeability gas reservoir is subdivided into four subgroups. Meanwhile, the classification limit of each evaluation parameters is determined and different development recommendations are proposed for each subgroups of low permeability gas reservoir. The evaluation method refines the understanding of offshore low permeability gas reservoirs, avoids inaccurate classification results which occurred in using the same standard of classification for low permeability gas reservoirs, can better filter out the suitable for development gas reservoir under the current technology and economic conditions, also has certain reference significance to similar gas reservoir classification and evaluation.

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Stress Sensitivity Characteristics of Low Permeability Reservoirs

LUO Chuan, ZHOU Penggao, YANG Hu, SHI Jiangang

西南石油大学学报(自然科学版) 2020, 42 (1): 119-125. DOI: 10.11885/j.issn.1674-5086.2019.01.21.03

Abstract （184）

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Researchers disagree on the existence of high stress sensitivity in low permeability reservoirs, which has caused hindrance in the policy making in oil and gas production. The focus of these disagreement is to determine if the core undergoes plastic deformation during permeability stress sensitivity tests, if a micro-gap exists between the core and envelope, and if such a gap exhibits significant influences on the experimental results. In view of the incapability of traditional experiments to verify the plastic deformation of the core, the current experimental method is improved by performing mechanical tests on the core before and after conducting the permeability tests. Based on the theories of elastic mechanics and effective stress, the theoretical formula of stress sensitivity evaluation is deduced and quantitatively calculated. Experimental and theoretical results showed that during the stress sensitivity tests, the effective stress on the core is below the elastic limit, indicating that the core do not undergo plastic deformation. A micro-gap is found between the core and envelope, which has a significant effect on the permeability test results and their variations. The permeability of a low permeability core measured under a low effective stress incur considerable measurement errors. The existence of the micro-gap leads to an overestimation of stress sensitivity of the core. During the experiments, the core strain is diminutive, and the resulting change in permeability is extremely small. Therefore, it is concluded that there is no strong stress sensitivity present in the low permeability reservoirs, and in general, the lower is the permeability of the rock, the lower is the stress sensitivity.

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Researches on Relationship Between Production Allocation and Decline Rate of Gas Wells in Sulige Gas Field

LI Peng, FAN Qianqian, HUO Minghui, ZHENG Lanian, YUE Jun

西南石油大学学报(自然科学版) 2020, 42 (1): 126-132. DOI: 10.11885/j.issn.1674-5086.2018.12.07.01

Abstract （170）

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To determine the rational production allocation for gas wells with a certain initial decline rate, Arps decline curve analysis was used to clarify the positive proportionality between new well production allocation and its initial daily decline rate, assuming that the initial production allocation of the gas wells is not affected by their final cumulative gas production. The initial daily decline rate was then converted into the initial annual decline rate to determine the relationship between the gas well production allocation and the initial annual decline rate, and a theoretical chart was established for the degrees of reduction in gas well production and in the initial annual decline rate, which can be used to guide the rational production allocation of new gas wells and determine the workload for gas field capacity building. This study demonstrated that, in reducing production allocation to reduce gas well decline, the magnitude of reduction in gas well decline rate is related to the magnitude of the initial annual decline rate and the magnitude of the reduction in production allocation, rather than the absolute value of the reduction in production allocation. The larger the initial annual decline of the gas wells, the more significant is the reduction in gas well decline through reduction of production allocation. The opposite is observed for gas wells with relatively small initial annual decline, whose reduction decline is not significant through reduction of production allocation.

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Application of a Biosynthesis-based Drilling Fluid in the Changning Gas Field

FAN Yu, ZHONG Chengxu, MU Naiqu, JIN Xin, WU Pengcheng

西南石油大学学报(自然科学版) 2020, 42 (1): 133-139. DOI: 10.11885/j.issn.1674-5086.2018.12.21.01

Abstract （191）

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Oil-based drilling fluids used in horizontal shale gas wells, is of high risk of environmental pollution and is difficult dispose. To solve the problems, a novel and environmentally friendly drilling fluid system for shale gas wells was developed. Through the preparation of a biosynthesis-based oil and experimental evaluation of the performance of this formula, a waterin-oil emulsion drilling fluid system with modified vegetable oil as the continuous phase and brine as the dispersed phase was developed. The system, which does not contain aromatic hydrocarbon components, is biodegradable and meets environmental protection standards in wastes disposal. The biosynthesis-based drilling fluid was applied in three wells on the HA platform in Changning Gas Field. The results from this application show that the system possesses good inhibitive, sealing, and lubrication characteristics, ensureing smooth operations during drilling, electric logging and casing running, lowering environmental risks, and enabling low waste disposal costs.

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Material Balance Equation and Dynamic Reserve Calculation of CO ₂-rich Gas Reservoir

CHENG Tao, LUAN Xueying, WANG Wenjuan, LIU Pengchao, Lü Xindong

西南石油大学学报(自然科学版) 2020, 42 (1): 140-146. DOI: 10.11885/j.issn.1674-5086.2018.09.25.04

Abstract （163）

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For an accurate calculation of dynamic reserve during the depletion-drive development of CO ₂-rich gas reservoir, which is a consequence of release of dissolved gas, a material balance equation is established considering water encroachment, reservoir stress sensitivity, water vapor concentration, and release of dissolved gas. PVT experiments were performed to investigate changes in the solubility of natural gas mixtures with a CO ₂ concentration of 3.18%~53.90% when the pressure dropped from 53.01 MPa to 3.01 MPa. Based on the experimental results, a prediction model for solubility analysis was developed based on regression. To investigate the effect of high CO ₂ concentration on the dynamic reserve calculation of gas reservoirs, the latter (denoted by A) was calculated utilizing the pressure drop method, the reserve computation model only considering stress sensitivity, the reserve computation model considering stress sensitivity, water vapor concentration and water vapor expansion, as well as the proposed computation model that also considered high CO ₂ concentration. The results showed that when the effect of the release of CO ₂-rich natural gas was not considered, the calculated dynamic reserves were considerably high, with errors ranging from 0.69×108 m ³ to 2.55×10 ⁸ m ³. Therefore, its effect cannot be ignored in the evaluation of the dynamic reserve of gas reservoirs.

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The Theory of Pressure-difference-time and the Equivalence of Variables in Planar One-dimension Flow

LIU Hailong

西南石油大学学报(自然科学版) 2020, 42 (1): 147-154. DOI: 10.11885/j.issn.1674-5086.2019.05.15.01

Abstract （185）

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In view of the fact that the functional relationship between the active and passive variations of planar one-dimension flow needs to be clarified, the concept of pressure difference time is proposed. The author studies the functional relationship between the active and passive variations of planar one-dimension flow. In this study, the functional relationship between pressure difference time and cumulative water injection given in the author's literature is used in Buckley-leverett equation and Welge equation to derive the functional relationship between pressure difference time and water saturation, water ratio, cumulative oil production and the degree of reserve recovery. The following understandings have been obtained:there is a functional relationship between any two variables of planar one-dimension flow, which is determined by the parametric equation. Pressure Difference Time is the parameter of the parametric equation. Variables of planar one-dimension flow are equivalent. Based on the above understanding, taking the study of interlayer interference as an example, the mechanism of interlayer interference is studied by using the concept of pressure difference time and the equivalence of variables. Using the concept of pressure difference time and the knowledge of equivalence of variables, the author clarifies the functional relationship between active variable and passive variable, and the equivalence relationship between variables in displacement process. This understanding has a certain role in promoting the studies of theoretical issues and application issues.

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Influence of Gas Storage and Peak Shaving on Pipe Diameter Selection of Long-distance Pipeline

XIE Ying, ZHANG Jun

西南石油大学学报(自然科学版) 2020, 42 (1): 155-160. DOI: 10.11885/j.issn.1674-5086.2018.10.16.01

Abstract （182）

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In this study, gas storage and peak shaving were considered for pipe diameter selection of long-distance pipeline carrying natural gas, and the calculation methods of gas storage capacity and peak shaving demand at the end of the pipeline were summarized. With a certain long-distance natural gas pipeline project as an example, a method combining static and dynamic simulation was used because the natural gas consumption is non-uniform. First, hydraulic calculations were performed to obtain the corresponding pipe diameters, whose pipe capacities satisfy daily/monthly average and high monthly and high daily working conditions. Then, the demand of hourly/daily/monthly peak shaving was analyzed, and suitable pipe diameters were selected under the peak shaving working condition after comparing the storage and peak shaving capacity of the pipeline and the peak shaving demand. Accordingly, a detailed economic comparative analysis was performed on peak shaving in pipeline and in gas storage constructed, which indicated that appropriately increasing pipe diameter can not only satisfy the demand of hourly peak shaving and daily peak shaving, but also is more economical. The results show that, when selecting pipe diameter, pipeline peak shaving should be considered in order to obtain the optimal pipe diameter scheme via comprehensive comparison.

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Theoretical Research on Circumferential Stress of Four-point Bending Specimen of Unequal Thickness

LIAN Zhanghua, ZHANG Jin, WANG Yuhai, ZHANG Qiang, LIU Yonggang

西南石油大学学报(自然科学版) 2020, 42 (1): 161-169. DOI: 10.11885/j.issn.1674-5086.2018.08.30.03

Abstract （221）

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Straight beam specimens of equal thickness, which are standard four-point bending specimens, cannot be used to simulate the real working condition of the curved-beam structure of pipes. Therefore, a non-standard four-point bending specimen of unequal thickness was designed, which has a complete arc as the outer wall and a straight-line segment combined with two symmetrical arcs as the inner wall. Based on the structure and mechanical model of a four-point bending specimen with unequal thickness, a theoretical formula to calculate the circumferential tensile stress at any arbitrary point on the specimen's outer wall from the load of the specimen was derived. Further, a finite element mechanics calculation model for this four-point bending specimen was established. The results show that the absolute error of the maximum circumferential stress calculated by the theoretical formula derived in the paper was 0.06%~0.33% compared to the result by the finite element method. This indicates that there is almost no error, which fully proves the accuracy of the theoretical formula. The theoretical formula provides a simple method for calculating load parameters of stress-corrosion cracking experiments with the four-point bending specimen of unequal thickness.

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Corrosion Mechanisms of Tubing String of Coalbed Methane Wells in Eastern Gansu

CHEN Lichao, WANG Shengwei, ZHANG Diankun, GUO Dingding, REN Longfeng

西南石油大学学报(自然科学版) 2020, 42 (1): 170-180. DOI: 10.11885/j.issn.1674-5086.2018.07.07.01

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The perforation of the oil tubing string caused by the corrosion and the frequent stuck pumps in coalbed methane (CBM) wells are the key factors restricting the development of CBM resources in eastern Gansu. This paper, by using scanning electron microscopy (SEM) and secondary electron image (SE), back scattering (BSE) to characterize the microstructure of corrosion scale and the energy spectrum analysis (EDS) calibration element types and contents of corrosion products, and through X-ray diffraction analysis of component of products, the corrosion mechanisms and protection measures of tubing string of CBM wells were proposed:CO ₂ corrosion occurs to N80 steel of CBM Wells in this area in high salinity formation water, Cl ^-, HCO ₃ ^-, forming a multilayer structure corrosion scale (FeCO ₃). Due to the low bonding strength between the corrosion scale and metal matrix in the wellbore flow, medium scour easily occurs under the stripping, and corrosion scale is porous density, Cl ^- contacts the metal matrix to form autocatalytic galvanic corrosion, accelerate the localized anodic dissolution, and to generate a large number of spot corrosion pit, exacerbating the corrosion perforation damage. The selection of 3%Cr oil tubing, corrosion inhibitor (crude oil) and perforation completion is a feasible measure to realize the integral corrosion protection of tubing String of CBM wells in this area.

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Identification of the Complex Lithology of Mixed Rock

CHEN Gongyang, WANG Pengyu, GAO Yang, ZHANG Fang, YIN Senlin

西南石油大学学报(自然科学版) 2020, 42 (2): 1-14. DOI: 10.11885/j.issn.1674-5086.2019.04.08.01

Abstract （167）

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The Permian Lucaogou Formation in the Jimsar Sag is a set of terrigenous clastic and carbonate mineral mixed rock layers with complex and diverse mineral types. Currently, controversy still exists surrounding the naming conventions for the lithology of the Lucaogou Formation, which has greatly affected the efficiency of lithology identification at drilling sites. In this paper, X-ray fluorescence (XRF) and X-ray diffraction (XRD) were applied to the comprehensive analysis of the relationship between rock mineral composition and elemental content. By adopting the element cross-plot method, we established six types of lithological identification plots, including feldspar lithic sandstone, fine sandstone, mudstone, mudstone dolomite, sandy dolomite, and dolomitic sandstone. Comparative analysis revealed that the coincidence rate can reach 80%. This provides a good method for in situ lithology and sweet-spot identification of tight oil mixed rock, which could effectively guide lithology identification and geosteering of horizontal wells on site.

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Seismic Sedimentary Study on the Fan-delta of the Baikouquan Formation on the Western Slope of the Mahu Sag

LI Quan, LI Peijun, NI Zhen, LIU Jun, LIU Hechong

西南石油大学学报(自然科学版) 2020, 42 (2): 15-26. DOI: 10.11885/j.issn.1674-5086.2019.01.29.01

Abstract （144）

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Fan-delta front glutenite exhibits wide variation in physical properties, making it difficult to predict high-quality reservoirs. Aiming to address this key issue, we identified and described the sedimentary facies distribution characteristics and filling process of the fan-delta in Baikouquan Formation in the Fengnan region on the western slope of the Mahu Sag (Junggar Basin). The study was guided by seismic sedimentology theory, and was done by means of seismic lithology, seismic geomorphology, and stratigraphic slicing techniques with logging and seismic data. In this study, we first established a high-precision sequence stratigraphic framework of the Triassic Baikouquan Formation on the western slope of the Mahu Sag, and delineated six fourth-order sequences. Then, we identified the sedimentary microfacies of the diversion channels, river channels, fan-delta front subaqueous diversion channels, estuary dams, and sheeted sands, as well as the corresponding logging characteristics of the Baikouquan Formation in the study area. We also indicated the correspondence between reservoir sand bodies and seismic amplitude by lithology calibration. Finally, with the help of slicing techniques in a fourth-order sequence grid, we clarified the filling-evolution process of the fan-delta sedimentary system in the Baikouquan Formation and pointed out the distribution range of high-quality reservoirs in the fan-delta front and the consequent prospecting direction.

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The New Understanding and Exploration Significance in Triassic Baikouquan Formation of Eastern Mahu Sag

QIAN Haitao, YOU Xincai, WEI Yun, BAI Yu, WU Jun

西南石油大学学报(自然科学版) 2020, 42 (2): 27-36. DOI: 10.11885/j.issn.1674-5086.2018.10.21.01

Abstract （249）

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The oil and gas in the lower part of the second member of the Triassic Baikouquan Formation in the eastern Mahu Sag, Junggar Basin keep showing activity, and the industrial oil flow has been obtained in many Wells. However, there has been a dispute over the horizon of the gray sand conglomerate and the oil and gas layer. In order to further expand the exploration results of the Baikouquan Formation, we utilize the core, logging and seismic data, through the Paleogeomorphic restoration, waveform classification, and seismic attributes, to reclassify Baikouquan Formation, and analyze the paleogeomorphology, sedimentary facies belt and sedimentary model of the first Member of Baikouquan Formation. The results show that the Baikouquan Formation in this area is divided into 4 sections, which are superimposed step by step from bottom to top, and distributed in retrogradation and overlay; controlled by paleogeomorphology, three major provenance systems developed in the first Member of Baikouquan Formation, the front subfacies of fan-delta developed widely in the platform area of two flanks of the trench and the center of the sag; The three sets of oil layers developed from the bottom to the top, the lateral distribution being stable, and the closer to the center of the lake basin, the earlier of the oil and gas reservoir is formed; The reservoir of the first member of Baikouquan Formation is overlapped with the second member of Baikouquan formation reservoir of the high position of DA13 well block, which is characteristics of large area oil content. On the basis of the above new understanding, we pointed out that the first member of Baikouquan Formation is an important oil-bearing series in the study area, which is an important exploration area to find reservoir with economic sacle in the Baikouquan Formation.

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Cyclic Sequences and Microscopic Heterogeneity of Reservoirs in the Qigu Formation of the Fudong Slope Area

YU Jingwei, TANG Qunying, WU Jun, LU Ziyang, WEN Huaguo

西南石油大学学报(自然科学版) 2020, 42 (2): 37-47. DOI: 10.11885/j.issn.1674-5086.2018.11.28.03

Abstract （167）

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During the exploitation of Member 1 of the Qigu Formation in the Fudong slope area in the eastern part of the Jungar Basin, microscopic heterogeneity results in low oil and gas recovery and difficulties obtaining the residual oil. To solve these problems, this study investigated variations in the microscopic heterogeneity of (underwater) diversion channel reservoirs within cyclic sequences of different classes. Based on the sedimentary dynamics of the cyclic sequences and a stratigraphic framework with high-resolution sequences, quantitative evaluation of the heterogeneity of grains, filling materials, and reservoir pore and throat sizes was carried out mostly using mercury intrusion data of wells in the region. It is believed that the microscopic heterogeneity of the reservoirs with cyclic sequences of different classes differ. For short-term cycles, the microscopic heterogeneity of single (underwater) diversion channel reservoirs is strong at the bottom but weak at the top. For medium-term cycles, the microscopic heterogeneity of superimposed (underwater) diversion channel reservoirs is strong at the top but weak in the middle. Uplift or subsidence of cyclic sequences leads to changes in the relationships between available spaces and sediment sources. These are the main factors resulting in the differences microscopic heterogeneity of the reservoirs. And the heterogeneity of the original grains determines the heterogeneity of the reservoir pore and throat sizes.

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Relationships Between Sulfur-containing Compound Types in Crude Oil and Causes of Thermochemical Sulphate Reduction in Tazhong Area

YUAN Yuyang, WANG Tiankai, CAI Chunfang, XU Chenlu, QIN Qirong

西南石油大学学报(自然科学版) 2020, 42 (2): 48-60. DOI: 10.11885/j.issn.1674-5086.2018.10.27.30

Abstract （182）

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Various sulfur-containing compounds, such as thiophene, tetrahydrothiophene, benzothiophene dibenzothiophene, and thioadamantane, were detected in crude oil extracted from the Ordovician reservoirs in the Tazhong Area. These compounds differ in their contents and isotopic values for single-atom sulfur. The analysis results show that modifications of crude oil by thermochemical sulphate reduction (TSR) may be the cause of the differences. There is less tetrahydrothiophenes and thioadamantanes in the crude oil not modified by TSR. As crude oil is increasingly modified by TSR, the total dibenzothiophene (DBT) concentration increases. This indicates that DBTs are probably formed during TSR. Meanwhile, non-TSR-modified crude oil samples were compared to highly TSR-modified condensate oil samples from Cambrian reservoirs for their sulfur isotopic values and total thioadamantane concentrations. It was found that TSR can also change the sulfur isotopic values of crude oil. The DBTs and thioadamantanes in the highly TSR-modified crude oil samples have sulfur isotopic values of from 36‰ to 40‰. In contrast, the DBTs in slightly TSR-modified and non-TSR-modified crude oil from Ordovician reservoirs are mainly from cracking of source rocks; thus, their sulfur isotopic values are relatively low (～20‰) near that of kerogen in the Cambrian reservoirs. Thus, it is believed that the crude oil extracted from the Ordovician reservoirs in the Tarim Basin is mainly from Cambrian source rocks and the crude oil with higher organic sulfur isotopic values is mostly caused by TSR modification.

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Sedimentological Characteristics and Shale Gas Exploitation Potentials of the Foreland Basins of Xuefeng Mountain

LIU Chensheng, WANG Hui, SHI Le, FENG Ning

西南石油大学学报(自然科学版) 2020, 42 (2): 61-74. DOI: 10.11885/j.issn.1674-5086.2018.10.10.01

Abstract （167）

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The Silurian foreland basins of Xuefeng Mountain are distributed in the central and northwestern parts of Hunan and the Sichuan Basin and are the dominant basin type on the upper Yangtze Plate. However, at present, there are few studies the sedimentological characteristics and shale gas exploitation potentials of these foreland basins. Based on field survey and well logging data and test results, the sedimentological history and shale gas exploitation potentials of the foreland basins in the central and northwestern parts of Hunan were determined. The results show that the foredeep zones of the foreland basins in the central part of Hunan are dominated by turbidite fans and shallow marine continental shelf deposits. Meanwhile, there are various sedimentological facies in the post-uplift basins in the northwestern part of Hunan. These include tidal, shallow marine continental shelf, littoral, delta, and carbonate platform facies. Although the foredeep zones and the post-uplift basins significantly differ in their sedimentological facies and sedimentation thickness, the division of their sedimentation cycles is consistent. Hence, it is concluded that the foredeep zones and the post-uplift basins are interconnected and Xuefeng Mountain caused limited shielding effects on the basins along its two sides. Numerous geochemical analyses demonstrate that the organic carbon content and the organic matter type of the shales in the post-uplift basins of the study area are less than those of Jiaoshiba in the Sichuan Basin. The Silurian shales in the southern part of Hunan have relatively low values for various geochemical indexes mainly because the area has no black carbonaceous shales of the first sedimentation cycle found in the Longmaxi Formation.

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A Study on the Development of Sand-body Flow Barriers in Deep-water Turbidity Channels

LI Chenxi, YUAN Zhiwang, YANG Xipu, BU Fanqing, ZHAO Xiaoming

西南石油大学学报(自然科学版) 2020, 42 (2): 75-84. DOI: 10.11885/j.issn.1674-5086.2018.10.11.01

Abstract （164）

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Deep-water turbidites, due to their genesis, often display dramatic lateral variations, which makes the internal connectivity of the reservoir relatively complex. In deep-water exploration, flow barriers play a very important role in not only connectivity, along with other main factors, but also in effects of water injection between wells. Therefore, it is important to study how to depict flow barriers inside a reservoir between channels, and to characterize connectivity within a sand-body to optimize well locations and improve efficiency of water injection. Through a comprehensive study of the outcrops of gravity flow in the Gannan Area of China, along with logging, seismic, and production data of the Z group in the AKPO Oilfield in Nigeria, we analyze the formation of flow barriers, their distribution within sand bodies in complex water channels, and their effects on water injection. The results show that, for the injection and production well pairs, flow barriers that affect the sand-body connectivity exist in scatter, linear, and composite patterns. The patterns of the effects of injection and production can be linear, wavy, and scattering; the increase in water cut also differs in production wells of different injection and production patterns.

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The Research Progress of Well Logging Evaluation of Marine Natural Gas Hydrate

ZHOU Jian, SONG Yanjie, JIANG Yanjiao, SUN Qinshuai, JING Yanqing

西南石油大学学报(自然科学版) 2020, 42 (2): 85-93. DOI: 10.11885/j.issn.1674-5086.2019.10.10.01

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More and more attention has been paid to natural gas hydrates with huge resources. Aiming to slove the present problem of logging evaluation of marine gas hydrate reservoirs, this paper introduces the lattice structures, physical properties, distribution form and formation conditions. According to the physical properties and reservoir characteristics of natural gas hydrates, the logging response characteristics of natural gas hydrates are analyzed. Based on the literatures investigation, the main methods of calculating the porosity and saturation of natural gas hydrate reservoir by logging method are obtained, the shale content and saturation of the natural gas hydrate reservoir in Shenhu of South China Sea are evaluated. It is suggested that the existence of shale should be considered in the study of natural gas hydrates by synthetic artificial core in laboratory. By summarizing the research results of well logging evaluation of marine gas hydrate, this paper provides an important basis for future large-scale prediction of marine gas hydrate reserves and exploration and development, and has important practical significance for effective exploitation of natural gas hydrate resources.

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Predicting the Diffusive Front of Supercritical CO ₂ in Tight Oil Reservoirs

WEI Bing, SHANG Jing, PU Wanfen, Kadet VALERIY, ZHAO Jinzhou

西南石油大学学报(自然科学版) 2020, 42 (2): 94-102. DOI: 10.11885/j.issn.1674-5086.2019.10.30.02

Abstract （224）

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Most of researchers claim that supercritical CO ₂ diffusion is one of the key considerations for CO ₂ huff-puff EOR in tight reservoirs. In this paper, a matrix-fracture model was designed and applied to measuring the diffusion coefficient of supercritical CO ₂ in saturated oil cores using pressure decay method. The influence of reservoir conditions such as pressure and core petroproperties on the diffusion coefficient and concentration distribution of supercritical CO ₂ was comprehensively investigated, and a method predicting CO ₂ concentration field and diffusion front was established. The experimental results showed that the diffusion coefficient of supercritical CO ₂ in the tight core (0.06 mD) is in the order of 10 ^-12 m ²/s. The diffusion coefficient was found to increase with the increase of the initial gas injection pressure before finally leveling off after a certain pressure. The maximum diffusion coefficient occured around the critical pressure point. In addition, the diffusion coefficient increased with the increase of matrix permeability and porosity, whereas it decreased with the increase of core tortuosity. After 900 days, diffusion in tight reservoirs, the diffusion front only advanced 0.095 m. Therefore, it is rational to neglect the diffusing effect of CO ₂ in the field operation cycle of CO ₂ injection in tight reservoirs. In the later stage of diffusion, the concentration gradient of CO ₂ became low leading to gradual decrease of diffusion.

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Optimization of Injection Technique of Corrosion Inhibitor in CO ₂-flooding Oil Recovery

ZHANG Deping, MA Feng, WU Yule, DONG Zehua

西南石油大学学报(自然科学版) 2020, 42 (2): 103-109. DOI: 10.11885/j.issn.1674-5086.2019.05.08.01

Abstract （168）

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Severe downhole corrosion occurred during Jilin CO ₂ flooding in an oilfield in Jilin due to the high pressure of CO ₂, high concentration of saline water and sulfate reducing bacteria (SRB) in the produced fluid. Currently, addition of corrosion inhibitors is one of the common methods to protect the oil well and tubes. Through studies of corrosion mechanism and main factor analysis, the effects of inhibitor type, concentration, and injection technique on their filed inhibition efficiency and long-term durability were investigated, aiming at lowering the cost of corrosion management. Then a suitable injection regulation of inhibitor is proposed based on the filed situation in order to improve the long-term efficacy of inhibitor. Injection optimization tests indicate that the corrosion rate has been decreased to <0.076 mm/a. This optimized injection technique of inhibitor not only increases the service life of downhole device and tubes but also decrease the cost of corrosion management.

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A New Method for Rapid Evaluation of Shale Gas Content

LIANG Hongbin, ZHANG Liehui, CHEN Man, ZHAO Yulong, XIANG Zuping

西南石油大学学报(自然科学版) 2020, 42 (2): 110-117. DOI: 10.11885/j.issn.1674-5086.2019.03.29.02

Abstract （244）

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It is important to make clear the variation rule of shale gas content for make reasonable development plan of gas reservoir. However, it is difficult to obtain the characteristics of shale gas content as adsorbed gas flow with free gas after desorption during the development. Due to the influence of environment, equipment and human factors, the interpretation results based on the two common methods of logging interpretation and field desorption have great errors, which brings trouble to research on the development theory of shale gas reservoirs. Therefore, the physical model for shale gas isothermal adsorption experiment based on volume method is established by using Horsfield filling theory, and the method to determine the proportion of adsorbed gas and free gas is proposed. This method is verified to be feasible based on the measured data. Compared with well logging interpretation method and field desorption method, this method is more concise and accurate, and easier to calculate. Furthermore, the variation characteristics of adsorption gas and free gas can be quantitatively described by this method during the reservoirs development. The results show that when the reservoir pressure decreases significantly and the main gas source in the pore changes from free gas to adsorbed gas, the corresponding pressure of transition point is negatively linearly correlated with the porosity.

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Preliminary Study on the Mechanism of Abnormal High Pressure Formed by Oil and Gas Accumulation

HU Liming

西南石油大学学报(自然科学版) 2020, 42 (2): 118-124. DOI: 10.11885/j.issn.1674-5086.2019.04.17.01

Abstract （183）

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The formation mechanism of abnormal high pressure is very complex, and it is an unsolved academic problem, which needs to be further studied. By analyzing the characteristics of oil and gas migration, accumulation and reservoir drainage, the mechanism of abnormal high pressure formed by oil and gas accumulation is preliminarily explored from the aspects of "filling" power of oil and gas, quantitative calculation of abnormal high pressure, preservation and release of abnormal high pressure. The results show that the main driving force of oil and gas migration into reservoir is capillary pressure at the junction of reservoir and reservoir. The smaller the radius of pore capillary, the greater the power of oil and gas "filling" from reservoir to reservoir. The radius of pore capillary is one of the important factors affecting the maximum formation pressure coefficient in reservoir. The abnormal high pressure can be formed if the oil and gas volume of reservoir is slightly larger than the water discharged from reservoir; the abnormal high pressure in reservoir can be preserved by capillary pressure plugging; there is no capillary pressure at the reservoir-cap junction outside the oil and gas accumulation area, and the reservoir can release pressure through the drainage of caprock. The theory of abnormal high pressure formed by hydrocarbon accumulation can reasonably explain the fact that the pressure of most reservoirs is higher than that of hydrostatic column at the same depth, and that the formation pressure coefficient is slightly greater than 1.0, but high abnormal high pressure reservoirs is very few; it can also reasonably explain the cause of formation of high abnormal high pressure.

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A New Method for Calculating Permeability of Sandstone Reservoir

YU Hua, LINGHU Song, WANG Qian, GUO Qingming, WU Ying

西南石油大学学报(自然科学版) 2020, 42 (2): 125-132. DOI: 10.11885/j.issn.1674-5086.2019.03.01.01

Abstract （196）

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Reservoir permeability is an important parameter in oilfield development. It is the basis for determining reasonable exploitation scheme, optimizing completion perforation scheme and selecting the optimal drainage position. The common core statistical analysis method is of errors in permeability calculation and is of a small scope of theoretical applicability. To solve this problem, based on the serial capillary model, the mathematical relationship between reservoir microstructure parameters and porosity, permeability and formation factors is theoretically derived. The mathematical and physical equations of pore throat diameter ratio are established, and the theoretical calculation model of permeability based on porosity, pore throat diameter ratio and throat diameter reservoir microstructure parameters is established, and the micro physical influencing factors of permeability are clarified. Based on core experiment, logging data and permeability theoretical model, a new permeability calculation method is established. The results show that the permeability calculation results are in good agreement with the core analysis results, and meet the needs of accurate evaluation of reservoir permeability. The results show that the permeability of reservoir is the macro characterization of the micro pore throat structure parameters from the mathematical and physical point of view, and the research results provide a new way for the permeability evaluation of reservoir development.

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Influence of Time-varying Reservoir Physical Properties on Water Cone Change of Directional Wells in Heavy Oil and Bottom Water Reservoirs

ZHANG Jilei, LUO Xianbo, HE Yifan, OUYANG Yuwei, XU Ya'nan

西南石油大学学报(自然科学版) 2020, 42 (2): 133-140. DOI: 10.11885/j.issn.1674-5086.2019.01.24.03

Abstract （168）

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In view of the existing water cone variation formulas of directional wells in heavy oil and bottom water reservoirs, the changes of reservoir physical properties caused by long term large fluid volume scour have not been considered, which lead to the large sweep volume of water flooding, pessimistic understanding of remaining oil and poor reserve production degree and so on. In order to describe more accurately the variation law of water cone and the distribution of remaining oil between wells in high water cut stage, the variation law of reservoir physical property under long term large fluid volume scour is considered synthetically. The equivalent percolation resistance is used to characterize the permeability of the reservoir inside and outside the water cone, and the equation of numerical variation of heavy oil and bottom water reservoir considering physical property time variation is derived. Through the analysis of practical examples, it is found that the influence of reservoir physical property time variation on water cone is very significant. Under the same water cone width, the water cone height calculated by the water cone formula, which does not take account of the time-varying physical properties, is reduced by 46.3%. Compared with the results of log interpretation, the relative error is only 5.3%. The field pilot test proves the reliability of the water cone change formula of the directional well in the bottom water reservoir considering the time variation of physical properties. This reseach provides technical support for accurate description of water cone change and residual oil distribution law of heavy oil bottom water reservoir in high water cut stage under long term large liquid volume scour.

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Optimization Design of Well Pattern in Heterogeneous Gas Storage

LIU Pengcheng, YU Haojie, AN Hongyan, XU Wen, ZHU Yajun

西南石油大学学报(自然科学版) 2020, 42 (2): 141-148. DOI: 10.11885/j.issn.1674-5086.2019.05.29.04

Abstract （143）

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Gas storage well pattern design is very different from conventional gas field well pattern design. Under the same investment conditions, the conventional gas field well network design pursues the maximum recovery of gas field, while gas storage well network design pursues maximum working gas volume in one gas production cycle (3～4 months). Because of the great different of gas production capacity in different areas, one set of well pattern is not suitable for gas storage wells built on heterogeneous reservoirs. Taking Su A gas storage as an example, the area for gas storage network is divided into areas of high permeability and low permeability. We analyze the production capacity of gas wells in the two areas and the regional working gas volume variation with the number of gas wells. And we propose a non-uniform well pattern based on the maximization of working gas volume, and determine the reasonable well pattern density in high permeability zone and low permeability zone. When there are 11 wells in the gas storage, with non-uniform well pattern, the well pattern density in the high-permeability area is 1.7 wells/km ², and that in the low-permeability area is 0.38 wells/km ². The working gas volume of gas storage will be increased by 0.99×10 ⁸ m ³ than that of uniform well pattern.

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Impacts of Water Cross-formational Flow from Roof Rock on the Production Performance of Coalbed Methane Reservoirs

DU Jia

西南石油大学学报(自然科学版) 2020, 42 (2): 149-157. DOI: 10.11885/j.issn.1674-5086.2020.01.20.02

Abstract （136）

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Hydraulic fractures always penetrate into the roof rock. The water cross-formational flow from roof rock could apparently affect the production performance of CBM (coalbed methane) reservoirs. According to the crossflow effect on CBM production, two connection models are established to describe the geology relation between coalbed and top aquifer. Then, the effects of top aquifer on methane production performance is studied by numerical simulation under different hydraulic fracture conditions. Further, the production performance is plotted by dimensionless method and the water sources of well are judged in a case study. The results show that production schedule has a slight influence on water production when the water comes from the inner layer. For the top aquifer without a barrier, the fracture penetration ratio in aquifer will delay the gas production. Once the fracture penetrates the aquifer, the penetration ratio has less effect on production. For the top aquifer with a barrier, there exist two stages of gas production increase. When the penetration ratio is under 1/6, the gas production will increase first quickly and then slowly. When the penetration ratio is above 2/6, the gas production will increase first slowly and then quickly, and the production performance is less sensitive to penetration ratio.

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Contact Forms of Casing with Centralizer and Its Effect on Friction

HU Xihui, LI Wei, XU Bihua, MA Jinglun, YUAN Bin

西南石油大学学报(自然科学版) 2020, 42 (2): 158-165. DOI: 10.11885/j.issn.1674-5086.2019.04.08.02

Abstract （183）

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During the running casing operation, the casing will be bent and contact the well wall due to the influence of gravity and well trajectory. Therefore, an additional friction is generated, which affects running casing when it is too large. In particular, a large number of centralizers are used to ensure displacement efficiency and cementing quality in horizontal wells, which brings greater difficulties to running casing operations due to the increase of friction coefficient. Aiming to this problem, the paper first points out the three contact forms of the casing and the well wall:free state, point contact and line contact. It is also points out that the friction is different under different contact form. Then, the casing tortuous equation and contact from judgment model are built. According to the model segmentation calculation method, the friction of the casing under different contact modes is accurately calculated. The field example analysis shows that the method can accurately predict the friction and has a good guiding significance for calculating the friction.

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Research on Strength Behavior of Casing Thread with Defects in High Pressure Wells

ZHU Xiaohua, GUO Yingchun, DONG Liangliang

西南石油大学学报(自然科学版) 2020, 42 (2): 166-174. DOI: 10.11885/j.issn.1674-5086.2018.09.25.01

Abstract （143）

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There are few studies on the influence of casing defects on the bearing capacity of connecting threads in high pressure gas wells, and the casing safety evaluation cannot be supported by theory and data. Based on the above problems, the typical API 177.8 mm×12.65 mm P110 steel grade round threaded casing is taken as the research object. Based on the elastic mechanics theory and the corrosion casing mechanics model, the casing-cement ring-formation finite element model under different corrosion forms is established, and the casing thread tooth under the casing-formation-cement ring system is analyzed and studied. The stress distribution law of the threaded connection part under the influence of the stress distribution state and the three corrosion defects. The results show that the uniform corrosion has greater influence on casing thread maximum equivalent stress of high pressure wells than on low pressure wells; influence of pitting and groove corrosion defects on casing thread maximum equivalent stress effects were similar; pitting and groove corrosion defects in the bottom casing thread engagement segments exert significant influence. We also acquire the critical corrosion defect depth of casing under different corrosion defects. The research work in this paper provides a theoretical basis for safety assessment of casing threads in high pressure wells.

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Casing Damage Image Technology of Feature Pattern Recognition and Matching of Casing Damage Image and Its Application

HE Zhiming, WU Dong

西南石油大学学报(自然科学版) 2020, 42 (2): 175-181. DOI: 10.11885/j.issn.1674-5086.2019.03.29.01

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Aiming at the problem of casing damage and corrosion detection and recognition, four kinds of damage and corrosion types are defined, and the pattern matching recognition of damage and corrosion characteristics is studied. The traditional image contour tracking and extraction are optimized and improved. The casing damage image is transformed into three-dimensional one, and the feature pattern recognition technology of three-dimensional image is used to search a three-dimensional damage-corrosion closure volume, by constraining on distance thresholds between data points and numerical thresholds in casing damage data sets. Different three-dimensional damage-corrosion closure volume represent the different characteristic subsets of damage and corrosion shapes. The axial and radial features of the feature subset are extracted, and the extracted features are matched with the standard corrosion pattern features to accurately evaluate the damage-corrosion type of casing. Practical application shows that it can accurately detect ring corrosion, line corrosion, general corrosion and isolated corrosion, and solve the problem of identifying the corrosion type of casing damage at present.

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Preparation and Performance Evaluation of W/O Emulsion Plugging Agent Based on Cottonseed Bottom Oil

DONG Ruiqiang, ZHI Keke, GUO Lianghui, HE Long, LI Entian

西南石油大学学报(自然科学版) 2020, 42 (2): 182-188. DOI: 10.11885/j.issn.1674-5086.2019.01.10.01

Abstract （191）

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Cottonseed oil is a by-product of cottonseed oil press. Waste cottonseed oil will cause serious environmental pollution and waste of resources. In this paper, emulsified cottonseed oil is first used as a selective plugging agent. The W/O emulsion of cottonseed bottom oil with high water content was prepared by using suitable compound emulsifier and its performance was evaluated. The viscosifying interval of emulsion was studied by rheometer. The results show that the maximum viscosifying interval can reach 80%. The stability of the emulsion was studied by oil fraction. The stability of the emulsion increased with the increase of water content. The temperature and salt resistance of the cottonseed oil emulsification system was evaluated. The cottonseed oil emulsion could withstand high temperature at 110℃ and 2×10 ⁴ mg/L. Calcium ion; Newtonian properties of emulsions with different water content were studied by flow behavior index. The results showed that the higher water content, the weaker pseudoplasticity; sand-filled tube displacement experiment showed that the water and oil plugging rates of cottonseed oil emulsions were 98% and 15%, respectively, with good plugging performance and oil-water selectivity.

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