Table of Content

10 April 2025, Volume 47 Issue 2

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GEOLOGY EXPLORATION

Study on the Characteristics and Differences of Carbonate Reservoir in Halahatang-Fuman Oilfield

JIANG Tongwen, DENG Xingliang, LI Xuguang, CHANG Shaoying, WANG Peng

2025, 47(2):  1-17.  DOI: 10.11885/j.issn.1674-5086.2024.04.20.01

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The deep-ultra-deep carbonate reservoirs in the Tarim Basin have already formed a production base of 3 million tons of oil, but there is still controversy over the types of reservoir space and the structural differences of reservoir bodies in deep-ultra-deep carbonate rocks, which affect the optimization of oil and gas reservoir development schemes. Based on field outcrops, cores, seismic, logging, drilling and production data analysis, we conduct a comparative study on the types and structural differences of high-quality carbonate reservoir space and reservoir bodies in the Ordovician deep-ultra-deep strata of the Halahatan-Fuman Oilfield. The results show that: 1) Halahatang-Fuman Oilfield is controlled by the weakening of atmospheric freshwater dissolution from north to south: the main reservoir space types in the northern anticline karst area are karst caves and dissolution pores; the main reservoir space types in the southern interbedded karst area of Halahatan are fractures, pores, and cavity-type reservoirs and karst rivers; the main reservoir space types in the Fuman fault-controlled karst area are angular breccia intercavities and fault voids, and structural fractures. 2) The differences in reservoir space filling characteristics are also quite obvious: the karst caves in the northern anticline karst area and the interbedded karst area of Halahetang are relatively rich in dissolution filling, mainly including sedimentary filling materials, collapse filling materials, and chemical precipitation filling materials; however, the filling characteristics of the reservoir bodies in the Fuman Oilfield are relatively simple, mainly composed of calcite and silica cementation. 3) The differences in the internal structural features of reservoir spaces are as follows: the northern karst area has three layers of dissolution structures, namely, the surface karst belt, the percolation karst belt, and the subterranean karst belt; the southern interbedded karst area of Halahetang has three structural elements composed of the supply area, the percolation belt, and the discharge area; the fault-controlled karst area has four structural models, namely, the single sliding surface structure, the compressional nucleus belt structure, the tensile-torsional cavity nucleus belt structure, and the grille-like fracture network nucleus belt structure. Clearly recognizing the characteristics and internal structural differences of ultra-deep carbonate reservoir spaces is of great significance for the formulation of efficient oil and gas reservoir development plans in the Tarim Basin. It guides the deployment of wells and the optimization of well trajectories, leading to an increase in the success rate of high-yielding wells to over 96%, and provides new ideas for the next phase of efficient oil and gas exploration and development in the study area.

Distribution of the Thin Reservoir of Shoal Facies at the Top of Member 1 of the Jialingjiang Formation in Luzhou Palaeohigh

TANG Hao, LIAO Zichao, SUN Haofei, XU Chang, CHEN Xiao

2025, 47(2):  18-31.  DOI: 10.11885/j.issn.1674-5086.2024.04.27.01

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The first Member and second Member of the Lower Triassic Jialingjiang Formation in Luzhou Paleouplift are the main oil resources in Sichuan Basin, however, the reservoir especially the thin shoal reservoir distribution is not clear yet, which restricts oil exploration process. Based on core, cuttings and well logging data, this paper researches reservoir characteristics, reservoir genesis mechanism and paleogeomorphology, and get the following results. The reservoir lithology is mainly composed of thin-middle oolitic and bioclastic limestone, and the main reservoir space is the dissolved intragranular pores and moldic pores. The physical properties are generally poor, but high porosity and permeability layers are developed locally. The leaching of meteoric water is the main reservoir genesis mechanism, while paleouplift is the key to form reservoir by depositing grain shoals and syngenetic karstification. The well logging statistics show that the thickness of granulated rock in the first Member of Jialingjiang Formation is positively correlated with the thickness of strata, which indicates that the thickness of strata reflects the level of sedimentary palaeotopography. Therefore, it is considered that the central of Luzhou palaeouplift, the eastern margin of Kangdian palaeocontinental and the southern area of the central Sichuan palaeouplift are three main favorable areas for reservoir development. This research can be used as reference for the exploration and development of Jialingjiang Formation in Sichuan Basin, and more important it can also provide a case study for the distribution of thin shoal reservoir in the world.

Characteristics of Iron-bearing Carbonate Cements and Its Impact on Tight Sandstone Reservoirs in the Jurassic of the Taibei Sag

LIN Tong, ZHAO Zhenyu, WU Chao, ZHANG Hua

2025, 47(2):  32-49.  DOI: 10.11885/j.issn.1674-5086.2024.04.29.01

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The clastic rocks in the Middle-Lower Jurassic coal strata measures are important target for oil and gas exploration and development in Taibei Sag, Turpan-Hami Basin. Iron-bearing carbonate minerals are wildly distributed and the reservoir heterogeneity is strong. In addition, there are significant differences of oil and gas accumulation in different areas. Using various analysis testing. We make a systematic study on the carbonate minerals and paragenetic mineral in the reservoirs and clarify the main causes of reservoir heterogeneity. The study shows that the pores are filled by carbonate minerals to different extent, leading to the decrease of reservoir porosity and the enhancement of heterogeneity reservoir. The mineral assemblage and distribution are affected by the thickness, grain size and composition of sandstone related to sedimentation. The sandstone grain size of underwater distributary channel of braided river in Qiudong Depression is thick, coarse with complex debris and matrix content is poor. The sandstone of underwater distributary channel of braided river in Shengbei Depression is of thin-thickness, of fine grains with high content of plastic debris and matrix. Complex clastic components and high matrix content in sandstone lay the material foundation for the formation of iron-bearing carbonate minerals. The rock texture and quantity of organic matter in sediments determine the diagenetic evolutionary path of reservoirs in different intervals, and further lead to the spatial and temporal disparities of the mineral assemblage associated with iron carbonates.

Prediction of Pore Sweet Reservoir in Xujiahe Formation with Pre-stack Inversion Technique

SHI Xiulin, LI Ping, LI Jianbo, WANG Chun, REN Haixia

2025, 47(2):  50-69.  DOI: 10.11885/j.issn.1674-5086.2023.06.01.02

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Reservoir prediction of tight sandstone is always a difficult problem in the industry. Conventional post-stack impedance cannot distinguish between dense surrounding rock and high porosity sandstone effectively, and such problem is particularly typical in the study of tight sandstone reservoir prediction of Xujiahe Formation in Dayi Area, western Sichuan. To solve such problems, this paper carried out research by pre-stack technology. The petrophysical analysis shows that the velocity ratio of P-wave and S-wave has a good distinguishing effect on porous sandstone reservoirs, which indicates that the pre-stack technique can effectively solve the prediction problem. The properties of P-wave impedance, S-wave impedance and the velocity ratio between P-wave and S-wave are obtained by pre-stack inversion. With the help of lithofacies analysis technology, the sweet spot probability body of pore sandstone reservoir is generated, and the plane distribution of pore reservoir is predicted. The results show that the technique is effective and consistent with real drilling, which is of great significance to the exploration and development of tight sandstone field. This paper also elaborates the key technical links of pre-stack prediction, which included pre-stack optimization, partial stacking, petrophysical analysis, probabilistic model building, inversion calculation, and effect analysis of real drilling comparison. Each key link is critical to the reliability of the results. This method provides strong technical support for the study of tight sandstone reservoir prediction and has important guiding significance for continental exploration in western Sichuan.

Volcanic Reservoir Characteristics and Influencing Factors of Carboniferous Bashan Formation in Shazhang Fault-fold Belt, Eastern Junggar Basin

MAIMAITIYILI Pahading, WEI Bo, LI Xin, TIAN Jijun, ZHANG Zizhao

2025, 47(2):  70-83.  DOI: 10.11885/j.issn.1674-5086.2022.11.30.02

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The volcanic rocks of the Carboniferous Bashan Formation are widely developed in the Shazhang fault-fold belt in eastern Jungaer Basin, and the exploration and development of the carboniferous volcanic gas field in the adjacent Wucaiwan Sag indicates that the carboniferous volcanic rocks in the study area also have the potential of reservoir formation. To provide support for volcanic oil and gas exploration in this area, this paper comprehensively studies the characteristics of volcanic reservoirs and their influencing factors by using drilling, rock sample, the microscopic chip, imaging logging, analysis data. The results show that: 1) volcanic rock reservoir lithology of Bashan Formation is mainly composed of volcanic lava, fused volcanic breccia, pyroclastic rock, volcanic-sedimentary rock and sub-volcanic rock, which can be identified as eruptive facies, overflow facies, volcanic-sedimentary facies; 2) the main reservoir space is primary reservoir space (primary pores) and secondary reservoir space (secondary pores and fractures), and there are four types of reservoir space combination: pore + dissolved pores in almond body + fracture, pore + dissolution pore, dissolution pore + fracture and fracture; 3) the volcanic rock is of medium-low porosity and medium permeability reservoir with poor overall physical property and heteroqeneity; 4) the development of favorable volcanic reservoir in Bashan Formation is mainly controlled by lithology and lithofacies, weathering and leaching, and tectonic fragmentation.

OIL AND GAS ENGINEERING

A Study on Triaxial Compression Behavior of Digital Core Based on Equivalent Modulus Method

LIN Tiejun, ZENG Xin, SUN Xin, YU Hao, YU Wenshuai

2025, 47(2):  84-94.  DOI: 10.11885/j.issn.1674-5086.2024.06.24.01

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To address the challenges of coring in deep, hard, and brittle formations, such as difficulties in obtaining complete core samples and the high cost of indoor rock mechanics experiments, a numerical approach is employed. A multi-component digital core model, structured on a Voronoi polyhedron framework is established according to mineral composition content. An equivalent modulus method is proposed to dynamically adjust the mechanical properties of minerals under triaxial compression conditions. The digital core's triaxial compression process is simulated, yielding fracture patterns, stress-strain curves, and elastic modulus values, which align with indoor experimental results. A comparative analysis of the effects of triaxial pressure on the overall rock structure and mineral grains is conducted, focusing on damage and stress distribution. The findings reveal that the impact of triaxial pressure on mineral grains varies depending on the type and spatial distribution of minerals, while also inhibiting crack propagation in the rock. This approach and the results provide new insights into studies on the mechanical and fracture behavior of digital cores, and effectively simulates rock mechanics responses and fracture patterns under complex geological conditions, and offering technical support for solving the coring challenges in deep hard and brittle formations.

Coalbed Methane Fracturing Effect Prediction Based on FCMFS Feature Selection Algorithm

MIN Chao, GUO Xing, HUA Qing, ZHANG Na, ZHANG Xinhui

2025, 47(2):  95-104.  DOI: 10.11885/j.issn.1674-5086.2023.02.27.01

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It is difficult to analyze the nonlinear relationship between the fracturing effect and characteristics of coalbed methane from the mechanism level. Aiming at the problem, the internal relationship between the characteristics of coalbed methane fracturing effect is studied, and a prediction method of coalbed methane fracturing effect based on FCMFS feature selection algorithm is proposed. The method uses fuzzy comprehensive evaluation to calibrate the label, and uses genetic programming and XGBoost algorithm to construct and screen the characteristics of influencing factors, including two new structural features (stress ratio and genetic factors of geological construction) and six characteristics of perforation section thickness, permeability, fracture pressure, coal structure, gas saturation and sand strength. The experimental results show that based on the eight features constructed and screened by the FCMFS feature selection algorithm, combined with a variety of machine learning algorithms to predict the effect of coalbed methane fracturing, the accuracy, recall rate, and F1 classification evaluation indicators are improved by about 5%～10%. Among them, the Deep Forest algorithm has the best prediction classification effect on the training set and the test set, and the three classification evaluation indicators are all above 95% and 80%.

Mechanism and Applicability of AICD Water Control in Fractured Bottom Water Heavy Oil Reservoir

YANG Yong, SUN Changwei, JIANG Renkai, LI Xiaodong, LIU Yuanzhi

2025, 47(2):  105-114.  DOI: 10.11885/j.issn.1674-5086.2023.04.06.04

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Fractured bottom water heavy oil reservoir is the characteristic of micro-fracture development, high viscosity of crude oil and rapid rise of water cut. It is difficult to ensure the development effect by conventional horizontal well development. The development of such reservoir with strong bottom water control ability by horizontal well is always the main direction of development. Nanhai L Reservoir is a typical reservoir of this type. And has been put into production for more than 20 a, with recovery less than 12%, and comprehensive water cut more than 96%. The results of chemical water plugging and conventional ICD water control are poor. The development of high angle fractures is the main reason for the rapid rise of oilfield bottom water and poor development effect. At the same time, the crude oil in the reservoir matrix is difficult to be effectively used, and a large number of remaining oil still exists in the matrix and isolated karst caves. We analyze the mechanism of AICD water control, studies its applicability in combination with physical model, numerical model and field application, and conclude that AICD technology can improve the production of effective production intervals of horizontal wells in this kind of reservoir, and thus improve the development effect. According to the evaluation of well selection, AICD is a mechanism of controlling water and increasing oil production by controlling the flow of micro fracture and high permeability zone independently, balancing the liquid supply profile of horizontal well, improving the sweep efficiency of horizontal well and increasing the effective well control reserves.

Control Mechanism of CCUS-EOR for CO₂-rich Gas Injection in Bailian Condensate Reservoir

CUI Kai, CHEN Qiang, LIU Desheng, SUN Lei, WANG Yong

2025, 47(2):  115-126.  DOI: 10.11885/j.issn.1674-5086.2022.07.05.01

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To further improve the recovery of the remaining condensate oil and gas reservoirs in the depleted stage of Bailian structural oil and gas reservoir group in Fushan Sag, and to give full play to the comprehensive utilization benefits of the replacement development of CO$_2$-rich gas reservoirs in the Bailian structural belt, based on the development strategy of "carbon peaking and carbon neutralization", combined with the concept of independent carbon emission reduction and carbon neutralization during oil and gas reservoir development, Fushan Oilfield has established a development strategy based on CCUS-EOR technology to directly inject the associated gas recovered from CO$_2$-rich gas reservoirs in the Bailian structural belt into depleted condensate gas reservoirs. The phase analysis of the mixed-phase drive mechanism, the analysis of the long thin tube gas injection drive efficiency and minimum mixed-phase pressure, the analysis of the seepage characteristics of the gas-driven anticondensate in the reservoir core, and the numerical simulation of the gas injection drive components were carried out to study the control mechanism. It is found that gas injection can increase the remaining anticondensate saturation by 1.85 times. When gas injection pressure rises to 20.4 MPa, the mixed fluid can achieve a multiple-contact mixing phase. And the minimum engineering MMP is 21.13 MPa. The condensate recovery of long core mixed phase drive can reach 68.94%. The pilot test scheme of periodic gas injection assisted with gravity miscible flooding was determined and carried out. Numerical simulation and the monitoring of the change of flow composition and PVT phase analysis method in the field show that the control mechanism of the oil and gas transportation and the change of condensate and gas flow direction is the synergistic effect of dissolution and swelling, extraction, gravity mixed-phase drive and reservoir inhomogeneous flow, which provides a reference for the selection of CCUS-EOR technical policy for resuming production of condensate oil in subsequent production wells.

Influence of Undulating Feature of Horizontal Section of Shale Gas Well on Liquid Accumulation

HE Zhiguo, GAO Shangjun, LIU Yonghui, ZHAO Huiyan, ZAHNG Jing

2025, 47(2):  127-136.  DOI: 10.11885/j.issn.1674-5086.2023.03.14.01

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Horizontal well technology has been widely used as the main development technology in shale gas exploitation. Horizontal section of shale gas well has ultra-long, complex and changeable well trajectory. At the beginning of production, daily gas production and water production of gas well are large, and then daily gas production and water production rapidly decrease. Affected by many factors such as complex well trajectory, low gas production and low pressure, some gas wells have accumulated liquid in horizontal section. In order to solve the above problems, based on CFD simulation technology, this paper establishes borehole geometry model of typical horizontal section of wells, simulates and calculates gas-water two-phase flow characteristics and influence rules of upset structure in horizontal section under different operating conditions using Eulerian-Eulerian coupling Multi-Fluid VOF mixing method. The results show that with the increase of fluid flow rate, the liquid holdup curve of full borehole in horizontal section of upset structure fluctuates to varying degrees, and the concave point under borehole, At the uphill section of outlet, liquid phase is easy to fall back and causes accumulated liquid. The liquid accumulation height at the downhole of the well bore slowly decreases with the increase of gas flow rate, which can carry the liquid out of the well bore when the gas flow rate reaches 2.2 m/s. When the gas well is in low production period and the gas flow rate reaches the maximum 1.1 m/s, the liquid layer height is also more than half of the size of borehole inner diameter, and $h/D$ is about 0.55.

Establishment and Verification of the Wall Sticking Occurrence Temperature Calculation Model of Stratified Flow Pipeline

CHENG Xianwen, XIONG Jianhua, HUANG Qiyu, TIAN Jiaxing, YU Le

2025, 47(2):  137-150.  DOI: 10.11885/j.issn.1674-5086.2022.11.03.02

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Low temperature transportation technology can effectively reduce energy and economic loss for high-water-cut gathering and transportation pipelines. However, with the popularization of gas flooding, the fluids in many gathering pipelines are in the state of three-phase of oil, gas and water. In order to explore the effect of gas on the adhesion of gelled oil on the wall, a self-developed pressure-bearing stirring tank is used to measure the adhesion mass of gelled oil on the wall under different conditions. It is found that the gas dissolved in crude oil can significantly reduce the adhesion of gelled oil, while the temperature does not change with corresponding mass surge; subsequently, a gas injection test is carried out on the high water-cut gathering and transportation pipeline on site, and it shows that with the increase of the gas-oil ratio in the pipeline, the minimum inlet temperature decreases from 29 ℃ to 26 ℃, indicating that the presence of gas improves the fluidity of crude oil; finally, based on the theoretical basis of " wall shear stress=yield stress × coefficient", a stick-wall temperature calculation model that can be used in stratified flow gathering and transportation pipelines is established, and the verification shows that the model has a good calculation effect.

Stress Test and Analysis for Inlet and Outlet Pipeline System of the Station Under the Foundation Settlement

LIN Ruinan, YANG Hong, MAO Xuebin, HUANG Zhonghong, ZHANG Wen

2025, 47(2):  151-163.  DOI: 10.11885/j.issn.1674-5086.2022.07.10.02

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The foundation settlement easily leads to the stress concentration and excessive deformation of the inlet and outlet pipeline system of the natural gas station, and in severe cases, the pipeline may be damaged. To this end, a test platform for settlement stress testing of natural gas station inlet and outlet pipeline system including 2 typical structures of inlet and outlet lines, vent pipe and tee pipeline was built. Stress tests of different types of pipelines under foundation settlement were carried out. Based on the test platform, the three-dimensional model of the inlet and outlet pipeline system of the station was established to analyze the influence of internal pressure and diameter thickness ratio on pipeline stress. The results show that: the most serious bending deformation of the inlet and outlet line Ⅰ(buried manifold distribution structure) occurs at the ground elbow and the fixed position of the support, and the maximum tensile stress and compressive stress of the inlet and outlet line Ⅱ(Z-shaped structure) are both at the reducing tee of the pipe, the stress of the inlet and outlet line Ⅱ is smaller than that of the inlet and outlet line Ⅰ under the same settlement conditions; When the pier in the middle of the tee pipeline settles, and the stress of the pipeline at the inner side of the fixed supports at both ends and the settlement point far from the tee increases significantly with the settlement; When the ground-entry end of the vent pipe settles, and the vertical section of the ground-entry end has the most serious deformation, and the joint section between the vent pipe and the main pipeline receives the greatest stress. Reducing pipe diameter thickness ratio and operating internal pressure can reduce the equivalent stress during settlement and improve the pipeline safety. The research results provide a technical basis for the safety assessment, the selection of stress monitoring points and the settlement warning of the inlet and outlet pipeline system in natural gas station.

PETROLEUM MACHINERY AND OILFIELD CHEMISTRY

Corrosion Characteristics of X70 Steel Under AC-DC Mixed Interference

HE San, YU Rui, ZHANG Jianxiong, LI Bin, XU Huilan

2025, 47(2):  164-174.  DOI: 10.11885/j.issn.1674-5086.2023.07.31.01

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In certain areas, the cross or parallel installation of oil and gas pipelines, high-voltage transmission lines, and electrified railways creates the risk of AC-DC mixed interference corrosion in buried pipelines. Through electrochemical tests, combined with polarized light microscopy, three-dimensional optical microscopy, and XRD, the AC-DC mixed interference corrosion characteristics of X70 steel in the intersection area of electrified railways, high-voltage transmission lines, and natural gas pipelines were studied. The results show that: 1) the critical current density under AC-DC mixed interference is 120 A/m$^2$; 2) there is no positive correlation between the radius of capacitive reactance arc and current density under AC-DC mixed interference; 3) the AC-DC mixed interference anode area not only continued the corrosion intensity of DC interference, but also played the role of AC oscillation and pitting, resulting in secondary local damage in the corrosion pit, forming a large number of pitting and crevices, and gradually showing the phenomenon of etching which makes the partially corroded X70 steel (partially covered with a corrosion product film) unsupported and exfoliated in solution; 4) at the current density of 180 A/m$^2$, the corrosion depth of the specimen under AC-DC mixed interference reaches 250 μm.

Structure Design of Tubing Hanger for Deep Subsea Christmas Tree

ZHU Junlong, LI Yufang, RU Mengqi

2025, 47(2):  175-184.  DOI: 10.11885/j.issn.1674-5086.2023.10.07.03

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The subsea christmas tree is a critical piece of equipment for deep-sea oil and gas development. The tubing hanger, serving as a channel for oil and gas and an electricity, supports the tubing column and seals the annular space between the tubing and casing, making it a core component of the christmas tree. Its structural strength directly impacts the safety of oil and gas production. Taking the tubing hanger from an oil and gas field in the South China Sea as an example, and analyzing foreign tubing hangers, the main structural dimensions of the underwater christmas tree's tubing hanger were designed. Finite element analysis was employed to establish the finite element model of the tubing hanger, and numerical simulations were conducted for its operations during the lowering process, installation, normal production, and locking and unlocking procedures. The results indicated that during the lowering process, the maximum stress of the tubing hanger was 310.43 MPa, with a maximum deformation of 0.450 09 mm. During the installation process, the maximum stress was 310.43 MPa, with a maximum deformation of 0.408 85 mm. Under normal production conditions of 69 MPa and 64 ℃, the maximum stress at the oil outlet of the tubing hanger was 311.13 MPa, with a maximum deformation of 0.581 48 mm. At 69 MPa and 121 ℃, the maximum stress was 586.93 MPa, and the maximum deformation was 1.334 70 mm. The analysis shows that the designed tubing hanger meets the safety strength requirements, exhibits minimal deformation, and has good structural safety. This tubing hanger has been successfully applied to China's first domestically developed underwater christmas tree system, which plays a significant role in advancing the localization of China's underwater oil and gas production systems.