Table of Content

10 August 2022, Volume 44 Issue 4

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GEOLOGY EXPLORATION

Brittleness Characteristics of Organic-rich Shale and Its Relationship with Fracture Development of Changning Area

ZHAO Shengxian, LIU Yong, FENG Jiangrong, FAN Cunhui, JI Chunhai

2022, 44(4):  1-13.  DOI: 10.11885/j.issn.1674-5086.2020.07.20.01

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The brittleness of shale controls the formation and evolution of fractures, which is crucial to the volume transformation of shale gas reservoir and the production increase of shale gas well. Taking Longmaxi Formation in Changning area of South Sichuan as an example, the mineral composition, organic geochemistry, pore fracture structure and mechanical properties of the lower Long 1 sub section were tested by rock and mineral, geochemical and mechanical experiments. Combined with experimental method of scanning electron microscopy, the relationships between the fracture development and different shale characteristics of brittle minerals, organic matter and buried depth were analyzed. The results show that the organic-rich siliceous shale facie has the highest brittleness in lower Long 1sub section. The total content of brittle minerals such as quartz, feldspar, and pyrite is greater than 50%. They can regulate the shear slip of rock blocks, and the energy accumulated in the rock is greater than the energy required to complete the overall rock failure. The organic matter and the organic pores and microfractures produced in the process of maturity can promote the development, connection and connection of fractures. The higher the organic carbon content, the more developed the fracture system. With increasing burial depth, the brittleness of the shale decreases, and the rock failure mode changes from a complex cleavage type to a single shear type. The 1st and 2nd sublayers of lower Long 1 sub section have the highest content of brittle minerals and organic carbon, with brittleness indices of 61.31% and 60.70%, respectively. They can be selected as sweet spot section with good fracturing performance, and complex fractures can be formed after fracturing.

An Analysis of Distribution of Carboniferous Source Rocks and Exploration Potential Analysis in Eastern Junggar Basin

WU Xiaoning, DENG Yong, LIU Xiaohu, ZHU Feng, MIAO Jinpeng

2022, 44(4):  14-26.  DOI: 10.11885/j.issn.1674-5086.2020.11.18.02

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Well fu26 of Fudong Slope in eastern Junggar Basin obtained high yield flow in the carboniferous system and Well cheng1 of Gucheng Sag showed good results, revealed thick layer source rocks, confirming that the Carboniferous in the southeast of the Junggar Basin has a hydrocarbon source for the formation of large natural gas scenes. In order to further realize the exploration potential of Carboniferous natural gas in the east of Junggar Basin, this paper, based on the analysis of regional geological strata, structural pattern and well earthquake matching of Carboniferous system, comprehensively implements the range and scale of Carboniferous source rocks, and points out the direction of recent exploration in this area. The study of regional strata shows that Songkarsu Formation b is the main effective hydrocarbon source rock segment of carboniferous; the structural pattern analysis shows that Eastern Junggar Basin developed two major depression systems:the north and the south depression, the north depression has been discovered on a large scale, and the south depression developed large scale Carboniferous source rock, which is the key area to be explored in the next step; well-seismic matching analysis shows that there are mainly four major sags, Dongdaohaizi, Fukang, Jimsar and Gucheng in the south depression. Among them, the source rocks in Fukang and Jimusar depressions have wide distribution range, large thickness and high gas generation intensity, and have the resource basis for large-scale natural gas.

Arc Fault Characteristics and Implications for Petroleum Geology in the North of Bozhong Depression

WU Bin, HUANG Shengbing, GENG Mingyang, SHEN Pu

2022, 44(4):  27-36.  DOI: 10.11885/j.issn.1674-5086.2020.04.01.01

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The periphery of Bozhong Depression is an important oil-gas accumulation zone, but no oil-gas fields have been found in the north of Bozhong Depression so far. Faults are closely related to oil-gas, not only a controlling factor of the formation and evolution of traps, but also one of the important channels of oil-gas migration. Therefore, it is of great significance to study the structural characteristics of faults. Based on the detailed analysis of the three-dimensional seismic data in the north of Bozhong Depression, this paper analyzes the characteristics of fault development, activity, genetic mechanism and petroleum geological significance. The research results show that there are interlayer and stepped normal arc faults in the north of Bozhong Depression. In the vertical direction, the activity intensity of the fault is strong in the middle and weak on both sides. In the horizontal direction, the fault evolves into a simple lateral growth mode. Based on the comprehensive analysis of the fault growth index and faulted horizon, it is considered that the fault activity period should be from II segment of the Ed₂^L to the deposition of the Ed₂^U. The process of fault evolution is divided into four stages, including fault incubation period, fault activity period, fault migration period and fault static period. It is pointed out that both gravity sliding and strike sliding control the growth and development of arc fracture. It is considered that the growth and development of arc-shaped faults are beneficial to the formation of rolling anticline traps, to the control of the number and thickness of sand bodies, to the promotion of the communication between source rocks and reservoirs, and to the accumulation of oil and gas.

Evolution Mode and Genesis Analysis of Composite Point Bars

FAN Hongjun, WANG Xiabin, HU Guangyi, FAN Ting'en, HE Mingwei

2022, 44(4):  37-50.  DOI: 10.11885/j.issn.1674-5086.2020.05.19.04

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The composite point bar is composed of multi-stage residual bars to form a composite body. The internal structure of the reservoir is complex and highly heterogeneous. In the past, researches on point bars were mostly focused onthe shape, granularity, scale and hydrodynamic force. Quantitative research on and cause analysis on the "incompleteness" of point bars are rare. In this paper, the seismic section of McMurray Formation of early Cretaceous in Alberta Basin, satellite photos of Mississippi River New Madrid meander section, numerical simulation and physical simulation of meander rivers are selected to statistically fit the relationship between the evolution period of composite point bars and the residual degree. A similar logarithmic curve y=-a ln x + 1 can be obtained after two-dimensional coordinate axis projection. It is concluded that the evolution of composite point bars is in accordance with the following law:From the formation to the destruction into a defective state of a certain stage point bars, the degree of its defect (composite degree) is logarithmically decreasing with the evolution stage. The conclusion is valuable for the study of meandering river theory and the characterization of sand body.

An Experimental Study on Lamina and Fracture Mode of Shale

TANG Hongming, TANG Yuan, ZHENG Majia, LIU Jia, BIAN Yingying

2022, 44(4):  51-61.  DOI: 10.11885/j.issn.1674-5086.2020.10.08.02

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Shale lamina is well developed with strong micro heterogeneity. In order to form industrial gas flow in shale gas reservoir, fracturing must be carried out, and the fracture mode of shale is controlled by many factors. Taking the deep shale of Well X101 of Longmaxi Formation in South Sichuan as the research object, the relationship between shale fracture mode and mineral composition and occurrence of lamina is systematically studied by means of cores, thin section, logging data, X-ray diffraction and CT scanning, combined with uniaxial compression and conventional triaxial compression experiments. The results indicated that the cores with σ₁ perpendicular to the laminar direction of uniaxial compression form tensile splitting failure, which produce a vertical seam of about 80°; in the triaxial compression test, the cores with σ₁ perpendicular to the lamina form shear failure, the seam and the lamina intersecting obliquely at a high angle of 45°~65°; the rocks oblique crossing with the lamina at a 45° angle is mainly destroyed by shear slip along the grain plane. The results show that the rocks with σ₁ parallel lamina form conjugate shear failure, the seam formed by the two intersecting obliquely with the lamina at a low angle of 10°~45°. For rocks with different lamina occurrence, Young's modulus is significantly positively correlated with quartz content and negatively correlated with clay minerals. The correlation between compressive strength and the content of quartz and clay minerals are affected by different lamina dip angles. The development of siliceous lamina and the large thickness of single layer will enhance the mechanical properties of shale.

OIL AND GAS ENGINEERING

Research and Field Practice of Moderate Mild Water Injection Technology in Low Permeability Tight Reservoir

WANG Xiangzeng, GAO Tao, LIANG Quansheng, DANG Hailong

2022, 44(4):  62-70.  DOI: 10.11885/j.issn.1674-5086.2022.03.07.02

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In order to solve the technical problems of water phased channeling and flooding with fracture water, difficulties in recovery of matrix crude oil and low water drive recovery in ultra-low permeability tight reservoirs during water injection. In order to explore the effect of displacement rate on water drives recovery, we carry out the displacement experiment taking Chang-6 Reservoir of Ordos Basin as the research object. Then the NMR test results are analyzed, finally, the unsteady oilwater two-phase water flooding front propulsion mathematical model considering capillary force is established to form the policy method of moderate water injection technology. The results show that there is an optimal displacement rate in the process of water flooding, which makes the water flooding recovery maximum. The best displacement rate in the experiment is 0.06~0.08 mL/min. Taking the ZC Block of Yanchang Oil Production Plant as an example, moderate technical policies is adopted to control the water injection intensity in the block of 0.85~1.20 m³/(d·m), and the submergence of the oil pump is controlled at 100~150 m. After the application of the technology, production data show that the water flooding recovery is increased from 20% to 24%. Moderate mild water injection technology has a significant effect on EOR of low-permeability tight reservoir. The research results provide a reference for similar reservoirs in the process of high-efficiency water injection development.

Experimental of Water Drive Sweep Efficiency for Typical Stacking Mode of Deep Water Channel

YANG Li, HU Yisheng, LIU Guangwei, GUO Ping, YANG Baoquan

2022, 44(4):  71-80.  DOI: 10.11885/j.issn.1674-5086.2021.11.25.02

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Aiming at the typical deep-water turbidite composite stack channel model, a large-scale two-dimensional physical model was established, and the water drive laboratory experiment was carried out. The core-scale numerical simulation was further explored to study the influence of the different horizontal and vertical stacking ratio to the development performance. Results show that the middle part of the channel and the overlapping area are the main flow line area, with high sweep efficiency and displacement efficiency. While the sweep efficiency is low at the upper and lower parts of the channel with relatively poor physical properties, which also shows higher potential of remaining oil. The stacking ratio of channels in different phases is an important factor affecting the connectivity between injection and production wells and the remaining oil distribution. With higher horizontal and vertical stacking ratio, performance in the main streamline area becomes better, while the sweep efficiency in the non-main streamline area becomes worse. For the typical deep-water turbidite composite channel reservoir, it is recommended to maximize the perforation perfection of non-main sand bodies to increase sweep efficiency and increase recovery.

An Interpretable Machine Learning Approach to Prediction Horizontal Well Productivity

MA Xianlin, ZHOU Desheng, CAI Wenbin, LI Xianwen, HE Mingfang

2022, 44(4):  81-90.  DOI: 10.11885/j.issn.1674-5086.2021.10.23.01

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It is essential to predict multistage fractured horizontal well (MFHW) productivity of tight sand gas reservoirs for evaluation of hydraulic fracturing performance and optimization of hydraulic fracturing design. However, most of the current predictive methods introduce multiple assumptions and simplifications. Therefore, these methods cannot fully account for multi-scale fluid flow mechanisms in the tight formations of well productivity. A machine learning approach for predicting MFHW productivity is proposed. A well productivity model is built by machine learning algorithms to uncover hidden patterns in a data set including geological, fractured well productivity, drilling and completion data. In addition, to solve the "black box" issue of conventional machine learning modelling, the SHAP (SHapley Additive exPlanations) method is used to explain the built ML model globally and locally. The efficiency and practicality of the proposed method is demonstrated by the application to the Eastern Sulige Gas Field. Compared with petroleum reservoir simulation, the method not only improves the prediction performance of the well productivity, but also reduces modelling cycle and improve computational speed.

Stability Evaluation of Gaoquan Test Horizontal Well in Southern Margin Based on Finite Element Method

LIU Tao, LIU Feihang, MA Dudu, GUO Ling, WU Yue

2022, 44(4):  91-99.  DOI: 10.11885/j.issn.1674-5086.2020.10.29.01

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Qingshuihe Formation reservoir in Gaoquan Anticline in the south margin has the characteristics of high temperature, high pressure, high yield and ultra deepth. There is no mature completion case to follow in China. In this paper, the wellbore and formation stability models of pre perforated screen completion and casing perforation completion are established respectively for horizontal wells in target area, and numerical simulation study on wellbore stability in whole life cycle is carried out for opital completion mode. The results show that when the wellbore is along the direction of the minimum horizontal principal stress, the hole stress concentration is the maximum parallel to the minimum horizontal principal stress direction, and is the minimum perpendicular to the minimum horizontal principal stress direction, and the wellbore damage will start from the outer wall hole; the screen pipe and casing will only produce partial plastic deformation, with the deformation less than 5%, and small possibility of collapse, but the formation which screen tube completion is bound to collapse in the late production stage, and the perforated formation after cementing is relatively stable. Based on the wellbore stability, perforation can be preferentially recommended for such horizontal wells with similar characteristics in the target area.

Impact of Foam on the Permeability of Matrix-fracture Dual Systems and Evaluation Method

LI Qinzhi, WEI Bing, YANG Huaijun, ZHAO Jinzhou, KADET Valeriy

2022, 44(4):  100-110.  DOI: 10.11885/j.issn.1674-5086.2021.06.09.02

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As a favorable two-phase dispersive soft mater, foam is being extensively used for conformance control in heterogeneous reservoirs, gas channeling prevention in fractured reservoirs, and fracturing acidification in unconventional reservoirs. However, during transporting in matrix-fracture systems, foam usually leads to local capture, retention and accumulation, which might affect the permeability of the whole system especially matrix. In this study, we propose a method that assess the impact of foam on the permeability of matrix-fracture dual systems by using a surfactant foam and a cellulose nanofibrils (NCF) strengthened foam. The flow behaviors and distribution of foam systems in matrix-fracture systems are revealed. In total of four permeability-grade cores were used (0.13~239.60 mD), and the correlations between differential drop, invading depth, residual resistance factor and permeability are established. The results show that the foam could successfully flow through the cores with the permeability larger than 23.00 mD. The invasion of foam into low permeability(less than 3.13 mD) and tight-matrix leads to the reduction of permeability because of adsorption and/or mechanical retention. The influence degree of NCF foam is found to be analogous to that of surfactant foam. In addition, the foaming agent in the presence of NCF mainly retains on the fracture surface with few mass loss especially for the matrix with permeability lower than 8.50 mD. The permeability of the matrix is rapidly retrieved once the deposition is rinsed off the surface. The results of this study guide the investigation of foam transport and distribution in matrix-fracture systems especially for low permeability and tight matrix, and also provide method to assess the impact of foam on the permeability of matrix-fracture systems.

Study on Microscopic Flow Characteristics of Foam in Porous Media

JI Youjun, WANG Lilong, HAN Haishui, JIANG Guobin, WANG Zegen

2022, 44(4):  111-120.  DOI: 10.11885/j.issn.1674-5086.2020.05.05.02

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The flow behavior of foam in pores affects the sweep range and displacement efficiency, and plays an important role in enhancing oil recovery. Firstly, the single capillary model is established, and the level-set method is used to study the influence factors of foam flow in a single capillary tube. The Jia Min effect, coalescence mechanism and micro selective migration mechanism of foam in porous media are analyzed. The plugging performance of different types of foam is evaluated. Secondly, a real pore medium microscopic numerical model is constructed through CT image of XB Oilfield core, and the migration characteristics of foam in it are studied. The results show that the degree of foam deformation decreases with the increase of tube diameter ratio, and the contact angle of wetting wall has no effect on the rheological properties of the foam. The critical value of liquid velocity is N₂ when the radius of the 1.2 foam m bubble ruptures, and the pressure of the foam passes through the channel is directly proportional to the surface tension. The foam has the microscopic migration characteristics through the large channel, and the N₂ foam has strong stability and plugging property. It is suitable for profile control and flooding in low permeability oilfield at high water cut stage, which provides beneficial enlightenment for field application of gas-liquid dispersion system for profile control and oil recovery improvement.

Research and Application of Targeted Acidizing Tech in Horizontal Well of Carbonate Reservoir

XUE Heng, HE Bing, JIANG Liping, CAO Xianping, DUAN Ce

2022, 44(4):  121-128.  DOI: 10.11885/j.issn.1674-5086.2020.05.28.01

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The horizontal well greatly increase the flow area of oil. It's advantages are much higher than that of vertical well. However, the serious heterogeneity of the reservoir brings great challenges to the effective acid placement in horizontal well. Based on the development situation of carbonate reservoirs in the Middle East, this paper systematically analyzes the main technical difficulties faced by acidization of horizontal well. According to the different development stages of the oilfield, the targeted acidizing technology for horizontal wells are proposed. The three-dimensional radial acidizing simulation model for horizontal wells is also deduced. According to the simulation, the influence of acid placement patterns on the acidizing effect are analyzed for both new and old horizontal wells. The research shows that the targeted acid placement pattern based on the drilling damage is better than the uniformed, physical-based and cone-shaped acid placement pattern for new horizontal well; under the same acidizing effect, the targeted acidizing can save at least 10% acid use; the production index analysis of 5 acidized new wells shows that the targeted acidizing can improve the production performance of those wells well. For the acidizing of old horizontal wells, partial acidizing can effectively balance the production profile of horizontal wells; for the partial low-permeability interval with reconstruction, 1.5 in. coiled tubing can be used for jet acidizing, which can penetrate deep into the reservoir through acid wormhole; the analysis of acidization in 7 old wells conducted by re-acidizing shows that targeted acidizing can greatly improve the production capacity for old horizontal wells.

The Mechanisms and Innovative Applications of Over-saturated Particles Well Completion Technique in Limestone Reservoir

YANG Yong, LI Feng, ZHANG Wei, XIE Ribin, LI Xiaodong

2022, 44(4):  129-138.  DOI: 10.11885/j.issn.1674-5086.2020.07.15.01

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Liuhua reservoir in the east of South China Sea is a limestone reservoir, with a three-medium porous system, including matrix, fracture and pore. The water cut of oil wells goes up very fast. Various methods have been tried to solve this problem, but few effects have been achieved very. Based on the common particles filling technique, an over-saturated continuous pack-off technique is proposed and three wells have achieved obvious results. The water cut was 30% lower than adjacent wells and goes up much slower, the estimated ultimate recovery is 50 thousand m₃ more than designed. Due to the complexity of the geological and reservoir conditions, the mechanisms of this technique is controversial. This paper, based on the study of fractures, porous flow features, reservoir engineering method, well completion and reservoir simulation, studies the mechanisms of over-saturated particles, which are water control, fracture plug and formation remolding. At early stages, the main mechanism is formation remolding and fracture plug, over-saturated continuous pack-off injection amplifies the micro-fractures and connect the matrix. At later stages, water control is the main mechanism. This study will guide the further application of this technique to limestone reservoir and other bottom-water driven sandstone reservoirs.

A Study on Shape Memory Material for Gas Hydrate Well Completion

DUAN Youzhi, LIU Huanle, LIU Jinchun

2022, 44(4):  139-144.  DOI: 10.11885/j.issn.1674-5086.2020.05.20.02

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In order to solve the problem of sand production in the process of gas hydrate development more effectively, and ensure the stable and high yield of gas hydrate wells, the development of shape memory polymers for gas hydrate development is carried out. We choose the PCL/PM-200 system to synthesize open cell shape memory polyurethane foam in one step by combining physical foaming and chemical foaming. The shape memory polymers' memory properties, mechanical properties, thermal properties, cell structure properties are characterized and tested. The results show that the foam requires simple processing technology, and is of high shape recovery rate, good mechanical properties, uniform porosity, good temperature resistance and glass transition temperature, which is in line with the change of temperature-sensitive shape memory materials, which can meet the performance requirements of NGH shape memory materials. The system is used to produce shape memory material for gas hydrate development and to manufacture shape memory screen, which provides a new and effective well completion method for gas hydrate test and commercial development in the future.

Mechanism of Hydrogen Sulfide Generation During Tight Oil Development at Mahu

SHI Guoxin, WANG Fengqing, CAO Qiang, LUO Qiang, TIAN Hui

2022, 44(4):  145-152.  DOI: 10.11885/j.issn.1674-5086.2020.09.03.01

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In the development of tight oil in the Triassic Baikouquan Formation of Mahu Oilfield, hydrogen sulfide has been detected in 62 percent of production wells. In order to find out the cause of the generation of hydrogen sulfide, qualitative evaluation and quantitative analysis experiments have been applied to investigate the hydrogen sulfide generation by bacterial sulfate reduction and acid-rock reaction individually at reservoir condition. The results show that sulfate-reducing bacteria cannot multiply and produce hydrogen sulfide at 50℃ or in presence of bactericide. 4.34×10^-6 mol hydrogen sulfide are produced by the reaction of the 50.0 g of core powder with 15% hydrochloric acid. The primary cause of hydrogen sulfide generation is the reaction of hydrochloric acid and the acid volatile sulfide in the reservoir. The research results provide an important technical support for preventing generation of hydrogen sulfide and for maintaining the safety production of Mahu tight oil.

A Discussion on the Development of Intelligent Well Technology in Offshore Oilfield

FENG Gaocheng, YIN Yanjun, MA Liangshuai, ZHANG Liang, WANG Wei

2022, 44(4):  153-164.  DOI: 10.11885/j.issn.1674-5086.2020.06.02.01

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As offshore oilfields gradually enter the middle and late stages of development, it is more difficult to adjust injection and production. How to effectively use such difficult and marginal reserves has become an urgent technical problem. At present, the overseas intelligent well technology has been successfully applied for more than 20 years, while China's intelligent well displacement technology has just stepped into the best stage of leapforg development stage. Aiming at the needs of increasing production in offshore oilfield and the status of upgrading intelligent well, this paper reviews the theory and application of intelligent well technology at home and abroad. According to the development features and difficulties of continental sedimentary oilfield, the authors analyze the restriction in the leapfrog development of intelligent well technology in China offshore, and discuss the target direction and potential paths of the upgrading intelligent well technology. The studies have shown that it is of great potential for joint upgrading of intelligent well technology and digital oilfields. The breakthrough of technology has laid a solid foundation for systematic upgrade. The low-cost application of intelligent well technology has the great significance to increase the storage and production in offshore oilfield.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

A Study on Tri-axial Design Coefficient Based on Seal Integrity of Premium Connection

WANG Jiandong, LIN Yuanhua, LI Yufei, XIE Nanxing, DENG Kuanhai

2022, 44(4):  165-173.  DOI: 10.11885/j.issn.1674-5086.2020.05.19.01

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Aiming at the sealing integrity problem of tubing string in high temperature and high pressure gas well completion, the research on the tri-axis design coefficient of string is carried out based on the integrity analysis of a premium connection of gas seal on the 88.90 mm×6.45 mm 110SS steel grade tubing. In this study, API RP 5C5-2017 international standard connection performance test evaluation method is used to evaluate the load sealing test of a series full envelope under high temperature and room temperature environment. The dangerous load point and variation laws of seal energy and seal energy multiple are analyzed after second-time full envelope load cycles with different full envelope load (VME95% and VME 90%) according to gas seal energy criterion. Results show the seal energy and seal energy multiple as well as its variation law have to be further analyzed under full envelope load cycle by FEA, by which the safety applicable envelope load range need to be determined, although the gas seal premium connection has been evaluated by API standard seal integrity test. Therefore, the serviceability analysis of sealing performance has been performed after second-time full envelope load cycles with three kinds of full envelope load based on the full envelope load test evaluation and finite element simulation, and the safety applicable envelope load range and reasonable tri-axial safety factor have been determined under high temperature and ambient temperature environment. The research results have been applied successfully in some HTHP gas well. The research method presented in this paper provides useful guidance for the determination of safety factor of tri-axial design of tubing string.

Measurement Method and Application of Pipeline Polarization Potential Under Subway Disturbance

AN Jianchuan, ZHANG Wenyan, YU Zhongren

2022, 44(4):  174-182.  DOI: 10.11885/j.issn.1674-5086.2021.01.04.01

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The cathodic protection potential of the pipeline fluctuates frequently under the interference of subway. It is impossible to obtain the real protection potential of the pipeline through the traditional cut-off method. Considering that all external currents need to be disconnected, a new method is proposed to measure the polarization potential of the pipeline under the interference. Through field test and research, the main factors affecting the accurate measurement of pipeline polarization potential and their influencing rules are determined, and the parameter setting method of effective measurement of pipeline polarization potential under subway interference is established:the time when the polarization of the test piece reaches stability is at least 2.25 h, the embedding depth of coupon should not be less than 0.30 m. The recommended horizontal distance between the reference electrode and the coupon should be between 0.05 and 0.10 m.