Table of Content

10 February 2020, Volume 42 Issue 1

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

YANG Huaiyu

2020, 42(1):  1-9.  DOI: 10.11885/j.issn.1674-5086.2018.09.17.02

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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.

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

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

2020, 42(1):  10-18.  DOI: 10.11885/j.issn.1674-5086.2018.08.20.02

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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.

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

2020, 42(1):  19-32.  DOI: 10.11885/j.issn.1674-5086.2018.07.18.02

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To investigate the control of the syndepositional faults on the depositional fillings in the lower Ed₂, 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 Ed₂ segment layer. The lower Ed₂ 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.

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

WU Qun, YANG Yunfei, WANG Shufang

2020, 42(1):  33-44.  DOI: 10.11885/j.issn.1674-5086.2018.09.10.02

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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.

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

2020, 42(1):  45-56.  DOI: 10.11885/j.issn.1674-5086.2018.09.12.01

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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 (δ¹³C_PDB) and oxygen isotopes (δ¹⁸O_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.

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

WANG Youzhi

2020, 42(1):  57-68.  DOI: 10.11885/j.issn.1674-5086.2018.10.10.03

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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 T₂ 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 D₁, whereas D₂ 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 T₂ map are conducive to the development of coalbed methane.

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

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

2020, 42(1):  69-77.  DOI: 10.11885/j.issn.1674-5086.2018.09.10.03

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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.

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

WANG Qiwei

2020, 42(1):  78-83.  DOI: 10.11885/j.issn.1674-5086.2018.07.24.01

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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.

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

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

2020, 42(1):  84-90.  DOI: 10.11885/j.issn.1674-5086.2018.07.19.04

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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.

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

WANG Yanwei, LIU Huiqing, DONG Xiaohu, ZHANG Qichen

2020, 42(1):  91-100.  DOI: 10.11885/j.issn.1674-5086.2019.04.15.01

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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.

Percolation Resistance Characteristics of Water Drive in Offshore Light Oil Reservoirs

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

2020, 42(1):  101-110.  DOI: 10.11885/j.issn.1674-5086.2019.02.27.02

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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.

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

2020, 42(1):  111-118.  DOI: 10.11885/j.issn.1674-5086.2019.03.05.02

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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.

Stress Sensitivity Characteristics of Low Permeability Reservoirs

LUO Chuan, ZHOU Penggao, YANG Hu, SHI Jiangang

2020, 42(1):  119-125.  DOI: 10.11885/j.issn.1674-5086.2019.01.21.03

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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.

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

2020, 42(1):  126-132.  DOI: 10.11885/j.issn.1674-5086.2018.12.07.01

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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.

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

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

2020, 42(1):  133-139.  DOI: 10.11885/j.issn.1674-5086.2018.12.21.01

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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.

Material Balance Equation and Dynamic Reserve Calculation of CO₂-rich Gas Reservoir

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

2020, 42(1):  140-146.  DOI: 10.11885/j.issn.1674-5086.2018.09.25.04

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For an accurate calculation of dynamic reserve during the depletion-drive development of CO₂-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 CO₂ 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 CO₂ 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 CO₂ concentration. The results showed that when the effect of the release of CO₂-rich natural gas was not considered, the calculated dynamic reserves were considerably high, with errors ranging from 0.69×108 m³ to 2.55×10⁸ m³. Therefore, its effect cannot be ignored in the evaluation of the dynamic reserve of gas reservoirs.

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

LIU Hailong

2020, 42(1):  147-154.  DOI: 10.11885/j.issn.1674-5086.2019.05.15.01

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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.

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

XIE Ying, ZHANG Jun

2020, 42(1):  155-160.  DOI: 10.11885/j.issn.1674-5086.2018.10.16.01

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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.

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

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

2020, 42(1):  161-169.  DOI: 10.11885/j.issn.1674-5086.2018.08.30.03

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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.

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

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

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:CO₂ corrosion occurs to N80 steel of CBM Wells in this area in high salinity formation water, Cl^-, HCO₃^-, forming a multilayer structure corrosion scale (FeCO₃). 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.