Journal of Southwest Petroleum University(Science & Technology Edition)

The Pore Structure and Controlling Factors of High-porosity and Low-permeability Carbonate

TANG Hongming, PANG Yu, WANG Xiwei, ZHAO Yuchao

2023, 45(3): 1-13. DOI: 10.11885/j.issn.1674-5086.2021.04.09.01

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The Upper Cretaceous Khasib Formation carbonate reservoir of X Oilfield in the Middle East is a shallow-sea shelf deposit, it has the characteristics of multiple biological types and rock types, high porosity and low permeability reservoirs, and complex pore structure. Based on the Folk limestone classification scheme, this paper highlights the biological characteristics, and comprehensively compares the pore structure characteristics and control factors of different types of reservoirs on the basis of rock classification. Studies have shown that the reservoir rock types include four types of micrite bioclastic sand-clastic limestone, micrite algal clastic limestone, micrite bioclastic limestone and micritic planktonic foraminifera limestone; the type of pore structure can be divided into three types: high porosity and medium permeability medium throat type, high porosity and low permeability medium fine throat type, high porosity and low permeability fine throat type; the main factors affecting the pore structure are physical properties and structural components. Among different lithologies, the difference in biological species and content affects the development of primary pores and the strength of later diagenesis, resulting in differences in pore structure. Among the same lithology, the content of plasters controls the quality of the pore structure.

Seismic Sedimentology Characterization of Fan-delta in Slope Belt of Eastern Liaohe Depression

HUANG Derong, ZHANG Xianguo, WANG Youjing, CAI Guogang, XIE Baoguo

2023, 45(3): 14-28. DOI: 10.11885/j.issn.1674-5086.2021.11.21.01

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Fan delta is an important type of oil and gas reservoir in slope zone of faulted basin. Lithology and sedimentary facies vary laterally. It is difficult to characterize sedimentary facies distribution inter-wells. A typical fan-delta deposition at Tiejianglu Area in the gentle slope zone of the eastern Liaohe Sag is studied. i. Two work are carried on including isochronicity analysis of seismic reflection, and seismic characterization of sedimentary facies with multi-attributes fusion. The study reveals: 1) in fan delta deposition area, there are diachronous seismic events locally and frequency division dip difference analysis can identify significant diachronous seismic reflection; 2) the root mean square amplitude, energy half-time and skew in amplitude attributes contain the information of sandstone development degree and lithologic combination. RGB fusion of the three attributes provides a simple and effective method for seismic characterization of sedimentary facies in sparse-borehole areas; 3) in study area, there developed 3 fan deltas including 2 large fan deltas of north provenance and a small fan delta of southeast provenance. At present, the exploration and development are concentrated on the fan deltas of north provenance. This study provides an effective method for seismic characterization of fan delta sedimentary facies in gentle slope zone, and provides direction and target for further exploration in the study area.

Study on Quantitative Well Logging Interpretation of Continental Shale Oil Reservoir in Jimusar Sag

TAN Fengqi, LI Xiankun, GAO Yang, LI Yingyan, ZHANG Fang

2023, 45(3): 29-48. DOI: 10.11885/j.issn.1674-5086.2021.04.07.01

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The continental shale oil of Permian Lucaogou Formation in Jimusar Sag is selected as the research object to establish quantitative well logging interpretation models. Core calibration logging and data mining are used to establish the quantitative well logging interpretation models of physical properties, oil-bearing properties, micro pore structure and rock mechanics respectively according to the upper and lower sweet spot. In the field application of well logging interpretation models, the accuracy of reservoir evaluation has been greatly improved, reaching more than 85%. The three well logging curves are selected by the data mining method with the multi-factor permeability calculation model, not only reflect the contribution of absolute porosity to permeability, but also consider the restriction of micro pore structure transformation on permeability, and two well logging curves of natural gamma ray and acoustic time difference are used to characterize respectively the influence of shale content and compaction-cementation effect on seepage path and seepage resistance. Compared with the single factor model, the calculation accuracy is improved by 25.6%. In addition, due to the following influences such as the borehole environment, the gravity differentiation of pore fluid and the anisotropy of formation in different directions, there is a certain deviation between horizontal and vertical well logging curves. So the quantitative well logging interpretation models based on the response characteristics of vertical well logging curves and core analysis data can not be directly applied to the reservoir evaluation of horizontal wells. In view of the above problems, the conversion chart and calculation formula of well logging curves of two measurement methods are established, and the reservoir of the horizontal section can be quantitatively interpreted.

Stratigraphic Division and Exploration Potential Analysis of Lower Carboniferous in Chepaizi Uplift, Northwestern Junggar Basin

BIAN Baoli, HU Xiuquan, WANG Xueyong, LIU Hailei, CHENG Jinxiang

2023, 45(3): 49-60. DOI: 10.11885/j.issn.1674-5086.2021.04.20.01

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This study uses field outcrops, earthquakes, and the latest drilling and logging data to subdivide the Lower Carboniferous strata in the Chepaizi Uplift, and to conduct exploration potential analysis. Our research indicates that the lower Carboniferous strata in the Chepaizi Uplift have obvious three-division characteristics. From bottom to top, there are volcanic rocks of the Tailegula Formation, interbedded volcanic rocks and sedimentary rocks of the Baogutu Formation, sedimentary rocks of the Xibekulas Formation, and three sets of strata in the rock. There are obvious differences in characteristics, logging response, and seismic reflection. In horizontal direction, the Tailgula Formation is distributed throughout the region, with north-south concave and uplifts alternating. The Baogutu Formation and the Xibekulas Formation spread out in a north-south direction, eroding and pinching east to west. In general, volcanic reservoirs are better than sand-conglomerate reservoirs, and volcanic breccias have better physical properties than andesite. The explosive facies and intermediate-basic overflow facies of the Tailegula Formation are the dominant lithofacies for reservoir development, especially the explosive facies development area in the southeast, which is located in the range of medium magnetic anomalies with wide distribution and great exploration potential.

Oil & Gas Potential Characterization and Evaluation of Typical Continental Shale-sandstone in Northern Sichuan Basin

OU Chenghua, LI Hang, SHI Baiqiang, ZHANG Zhiyue, HE Jian

2023, 45(3): 61-71. DOI: 10.11885/j.issn.1674-5086.2021.08.08.01

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The Qianfoya Formation in northern Sichuan Basin is rich in oil & gas resources and it is expecting to exploration and development. On basis of core analysis, logging interpretation and sedimentary microfacies analysis, we analyze the vertical, horizontal and plane distribution characteristics of reservoir, find five types of the continental shale-sandstone oil & gas reservoirs, such as multi-layer tight sandstone oil & gas reservoir, upper shale-lower sand oil & gas reservoir, sand-shale interbedded oil & gas reservoir, shale-clad sand oil & gas reservoir and isolated oil & gas reservoir, evaluate total 44 oil & gas reservoirs in each layer, and select the three favorable oil & gas reservoir A, B, and C in the Qianfoya Formation in the study area. The above results are conducive to the further development of the continental shale oil & gas reservoir geology in China.

Engineering Geological Mechanics Issues and Research Methods in Oil and Gas Exploration and Development

LI Gao, ZHANG Yi, YANG Xu

2023, 45(3): 72-80. DOI: 10.11885/j.issn.1674-5086.2023.02.26.01

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The role of engineering geomechanics research in complex oil and gas reservoir exploration and development, as well as in integrated geological engineering, is becoming increasingly important. However, there are still many issues that need to be explored, among which the most critical is the insufficient integration of the geological evolution and mechanics research of stratum rocks. By taking the rock mechanics properties that vary with geological evolution as the intrinsic connection, this approach integrates sedimentary facies, diagenesis, tectonic evolution, and engineering impacts to more closely combine geological and engineering factors in engineering geomechanics research. The new method formed emphasizes building regional three-dimensional geological structural models and assigning rock mechanics parameters across regional-well zone-single well scales according to the geological evolution characteristics of different rock types. After establishing regional rock mechanics phases, the parameter fields are inversely corrected by combining the interference mechanisms of well engineering, thereby optimizing and adjusting well engineering design, improving the accuracy of regional geological understanding and geological information prediction. This provides scientific research methods for stress evaluation, fracture distribution prediction, pore pressure system analysis, and productivity evaluation.

A New Organic Amine Completion Fluid for Long-term Reservoir Protection

SUN Wenhua, LU Aiting

2023, 45(3): 81-88. DOI: 10.11885/j.issn.1674-5086.2022.11.11.01

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The Ugandan oil field is characteristic of high content of clay minerals in the reservoir; the long time contact of the completion fluid and the reservoir at the bottom of the well can damage the reservoir. In order to handle these problems, a new type of completion fluid with organic amine (PF-NETROL) is elaborated in this research. The inhibition test of the completion fluid is first of all utilized to determine the dosage ratio of organic amine in the completion fluid, then the reservoir protection performance test is conducted to verify the long-term effect of the optimized completion fluid on the reservoir protection. The experimental results showed that the anti-swelling rate that was initially 85.42% increased to 94.21% after being placed for one day in the completion fluid with different content of organic amine (PF-NETROL) proving that the anti-swelling effect with the organic amine is good; the anti-swelling rate of the completion fluid system with a dosage of 2% is still more than 90% after 90 d of placement and it maintained a good inhibition on bentonite; in addition, the completion fluid of the system has the least damage to the reservoir within 0~30 d and the pollution rate increased quickly after 30 d. The completion fluid with a dosage of 2% organic amine (PF-NETROL) is preferred as the completion fluid system of the oilfield in Uganda; therefore it is recommended to replace and supplement the completion fluid every 30 d in the actual operation to ensure the performance of the completion fluid and provide guarantee for long-term operation. The new organic amine (PF-NETROL) completion fluid formula proposed in this paper can play referrable effect on long-term completion fluid reservoir protection.

Drilling Fluid Technology for Gaoquan Anticlinal Wells in the Southern Margin of Junggar Basin

XU Shengjiang, WU Baocheng, XU Xinniu, YE Cheng, HUANG Hong

2023, 45(3): 89-97. DOI: 10.11885/j.issn.1674-5086.2021.04.29.08

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In view of the characteristics of the strata encountered in drilling the Gaoquan structure in the southern margin of Junggar Basin, the technical difficulties in this area were proposed. We analyzed the drilled well data and mineral composition and mechanical characteristics and found problems like a narrow drilling safety density window and large surface-subsurface temperature difference. Combined with the field conditions, the drilling fluid systems adapted to upper strata and middle and lower strata respectively are given. We proposed that a strong inhibiting water-based system; a medium density and strong sealing oil-based drilling fluid system is applied to the hard and brittle mudstone formation of Taxihe Formation in the middle and lower strata; and oil-based drilling fluid system with low filtration loss is applied to strong water-sensitive formation of Anjihaihe Formation. The results show that the strong inhibiting water-based drilling fluid system can effectively prevent collapse and pipe stuck in the upper part of the Gaoquan anticline formation on the southern margin; the high-density oil-based drilling fluid used in the middle and lower part of the formation has excellent anti-collapse and anti-leakage performance, with a temperature resistance range of -10 ℃ to 240 ℃, and can resist up to 40% brine intrusion and 10% water-sensitive cuttings contamination. The drilling fluid technology provides important technical support for the major oil and gas discovery in the Gaoquan structure, and can be used as a reference for drilling fluid solutions for exploratory wells in similar areas and formations.

A Study on Improving Heavy Oil Recovery by Solvent Assisted Steam Flooding in Late Stage

LIU Jiali, HUANG Siyuan, JIANG Qi, WANG Hongyuan, WANG Zhongyuan

2023, 45(3): 98-108. DOI: 10.11885/j.issn.1674-5086.2021.05.19.02

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This paper takes the Xing VI Group super-heavy oil reservoir in Block Du 84 of Liaohe Oilfield as the research object, and conducts an indoor evaluation study on solvent assist as a replacement technology to improve the efficiency of SAGD production. According to the current operating pressure in the SAGD steam chamber, hexane, which has a temperature similar to the steam dew point, was screened as an auxiliary additive for SAGD. In the laboratory, we first studied the evaluation of the viscosity reduction effect of heavy oil at different temperatures, solvent types and concentrations, and carried out comparison experiments of oil displacement efficiency between hexane-assisted steam flooding and pure steam flooding at different concentrations. Through solvent-assisted analysis of water cut, remaining oil saturation and final recovery improvement degree in the later stage of steam flooding, the influence of steam temperature and solvent concentration on steam flooding efficiency are revealed. The research results in this paper provide theoretical support for using solvents to assist in improving the efficiency of heavy oil recovery and optimizing on-site operating parameters in the later stage of SAGD development.

Apparent Permeability Model Considering Different Pore Characteristics of Shale Matrix

LI Heting, ZENG Jie, LI Zhenxiang, LU Qianli

2023, 45(3): 109-118. DOI: 10.11885/j.issn.1674-5086.2022.10.08.02

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Shale matrix stores a larger amount of gas and provides a long-term gas supply for shale gas production. Therefore, matrix permeability variation with the change of pore pressure directly affects long-term productivity. Micro- and nano-pores are well developed in shale matrix. These organic and inorganic pores involve different mechanical properties and gas transport mechanisms, the variation of effective stress and flow regimes all affects their apparent permeability. Moreover, gas-adsorptioninduced organic matter swelling also influences the apparent permeability to varying degrees. Based on the poroelasticity theory, this paper establishes an apparent permeability model suitable for shale matrix with consideration of different mechanical properties and fluid flow mechanisms in organic and inorganic pores and gas-adsorption-induced deformation. The impacts of different pore properties are analyzed, and the controlling factors for apparent permeability evolution are figured out. Results indicate that shale matrix apparent permeability evolution is time-dependent during constant-pressure gas injection and depletion. The evolution process is mainly dominated by gas rarefaction effects, effective stress variation, and localized sorption-induced swelling or desorption-induced shrinkage near organic pores. These factors control apparent permeability at different times. The evolution process is also related to the ratios of the volume of organic and inorganic pores to the total pore volume.

A New Method for the Study of Sand Production in Gas Reservoir Storage

LIAO Wei, LUO Shuanghan, HU Shuyong, ZHANG Yunxin, LUO Haitao

2023, 45(3): 119-130. DOI: 10.11885/j.issn.1674-5086.2021.10.19.03

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Xinjiang H gas storage is affected by the strong injection and production operation mode of gas storage, and the risk of sand production is prone to occur in the reservoir during peak shaving and gas production. Once sand is produced, it will seriously affect the life and peak shaving capacity of the gas storage, and there is an urgent need for studies on sand production in the gas storage. It is difficult for regular research to ensure the capacity of gas storage for peak shaving and supply, and monitor sand production during the conventional experiment. In view of this, this paper proposes a new experimental method, that is, on the basis of the conventional sand displacement experiment, the pore size distribution and pore throat distribution before and after the core experiment are measured by the nuclear magnetic resonance instrument. This method solves the problem that the amount of sand produced is too small and difficult to monitor in the process of conventional sand production experiments, and explores the sand production law of formation more comprehensively from a microscopic point of view. Using this method, the influence of five factors such as flow velocity, production pressure difference, permeability, water content, and formation pressure drop on formation sand production is analyzed. The experimental results show that: 1) the higher the flow velocity, the core permeability and sand production volume; both increase first, then decrease, and finally remain unchanged; 2) the critical flow rate of H gas storage is 4.14 L/min, and the critical production pressure difference is 5 MPa; 3) the water cut and the formation pressure drop are affected by the pore size distribution, and are the main factors affecting sand production in H gas storage formation; 4) when H gas storage has no water production in the early stage, proper sand production will increase the permeability of the formation and increase the gas injection and production capacity of the gas well.

Leakage and Explosion Simulation Analysis of Injection Production Pipeline of Gas Storage Based on PHAST

CHEN Lei, ZHANG Zhe, ZHANG Xinpeng, LIU Qian, CHEN Guifang

2023, 45(3): 131-142. DOI: 10.11885/j.issn.1674-5086.2021.08.13.03

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In order to improve the safety in operation of injection, production and gathering pipeline in underground gas storage, aiming at the problem of casualties caused by pipeline leakage explosion, based on the field production characteristics of the gas storage operation area, the main influencing factors of pipeline leakage and explosion accident were analyzed using Fault Tree Method. In addition, simulated by PHAST software, the effect of injection production pipeline operating pressure and pipeline transmission medium on the consequences of leakage and explosion accident was quantitatively analyzed, and risk assessment of the accident was carried out. It showed that under the selected simulation parameters, the hazard range of pipeline accidents increases with the increase of pipeline operating pressure, and the high-risk areas formed by gas cloud diffusion and explosion shock waves are both small. The leakage of gas flow pipeline with wet gas transmission mode will cause various fire accidents such as jet fire and pool fire. The risk assessment curve intuitively showed the harm caused by the injection, production and gathering pipeline of the gas storage to the enterprise personnel around the well station, buildings and ground operators of the gas storage. The research conclusions of this paper can provide a reference basis for the construction of emergency plan system and the improvement of disposal capacity in the operation area of gas storage.

Numerical Simulation of CO₂ Associated Gas Mixing Process

ZHANG Tao, YANG Ruofan, CHANG Wenjie, CHEN Bin

2023, 45(3): 143-153. DOI: 10.11885/j.issn.1674-5086.2021.11.10.01

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In the late stage of CO₂ flooding production in low permeability oil and gas fields, the produced product is associated gas containing a large amount of CO₂. In the further production process, the associated gas from different sources needs to be measured and treated. In order to solve this problem, the geometric model and numerical model of CO₂ gas diffusion flow are established by Fluent software, and then we study the mixing distance of gas diffusion under field conditions, which provides a basis for the installation position of on-line Chromatograph. The results show that CO₂ associated gas from different gas sources is not fully mixed immediately after entering the mixing pipe; obvious mixing occurs after diffusion for a certain distance along the length direction of the pipe with the velocity on both sides gradually decreasing, and the concentration difference decreasing. With the increase of gas flow velocity and pressure, the homogeneous mixing distance of gas diffusion increases with the increase of component B. When the component content is A, B and C, the mass fraction of CO₂ and CH₄ reaches a stable value at about 40, 45 and 30 m. It is recommended to install a gas chromatograph at this position and select a sampling point for measurement.

Design and Optimization Analysis of Downhole Linear Generator Based on Orthogonal Test

ZHONG Gongxiang, SHEN Wei, LEI Pengyan, SONG Hua, ZHONG Shengji

2023, 45(3): 154-162. DOI: 10.11885/j.issn.1674-5086.2020.11.06.01

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Aiming at the disadvantage of low power generation in the existing downhole power supply mode and combining the advantages of linear power generation, a new cylindrical downhole linear induction power generation scheme is proposed, which generates induced current by the relative motion between the sucker rod and the oil pipe. According to the principle of existing electrical machinery, we complete the structural design of the cylinder type permanent magnet linear generator; then we use Ansoft Maxwell to analyze the no-load flux density, no-load induced electromotive force, resistive load and the power generation performance of the cylindrical permanent magnet generator under the condition of actual sealing, and verify the validity of the generator design. Finally, the key structural parameters are optimized by using the orthogonal experimental optimization method, taking distortion rate and power generation as the optimization objectives. The results show that the generator has low harmonic distortion rate, high power and good stability no matter under load or no load. It can effectively solve the problems of low efficiency and unstable performance of existing downhole generators.

Design of Combination Lifting Technology of Rod Pump and Ground Driving Screw Pump

YANG Zhi, KANG Lu, ZHANG Xinghua, CHEN Yong, YI Zhaolong

2023, 45(3): 163-170. DOI: 10.11885/j.issn.1674-5086.2020.11.14.01

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Along with the development of deep oil and gas fields such as Tarim, satisfying the technology of deep and large pumping in deep well has gradually become a reality. The pump setting depth is deepening, the single way of lifting tend to show some limitations and inefficiency, so we propose a combination of lifting technique of sucker rod pump and ground driving screw pump: the screw pump and plunger pump being installed on the same production string, and the relaying way of extracting oil carried out. In order to demonstrate the feasibility of the lifting technique of rod pump and ground drive screw pump, we analyze the working principle, flow matching and force condition of the rod pump and ground drive screw pump, and establish the suspension load calculation model of the combined lifting process of the rod pump and the ground driving screw pump in the deep pumping conditions of the well. Compared with sucker rod pump, the swabbing parameters in the same production case of combination lifting system of sucker rod pump and ground driving screw pump will increase the depth of pump and the range of displacement, and reduce the energy consumption by reducing the polished rod load of the pumping unit.

A Theoretical Study on the Corrosion and Scale Inhibition Performance of Polyepoxysuccinic Acid Derivatives

CHEN Xin, ZHANG Yizhen, CHEN Qin, LUO Liang

2023, 45(3): 171-180. DOI: 10.11885/j.issn.1674-5086.2022.09.22.02

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In the process of oil and gas field development, tubing corrosion and scaling frequently occur, which will cause huge economic losses and serious safety problems. Adding corrosion and scale inhibitor is an effective anti-corrosion and scale prevention method, which is widely used in petroleum and petrochemical fields. In recent years, with the enhancement of public awareness of environmental protection, environmentally friendly polyepoxysuccinic acid (PESA) has been widely studied. Using quantum chemistry and molecular dynamics simulation methods to study corrosion and scale inhibition performances of PESA and polyepoxysuccinic acid derivatives (MEA-PESA). The influences of quantum chemical parameters (frontier molecular orbital energy, energy gap, bulk hardness, and Fukui index) for the corrosion inhibition efficiency are discussed. The adsorption behaviors of eight kinds of corrosion and scale inhibitors on the metal and calcium carbonate surface are investigated by molecular dynamics simulation. The results of adsorption energy show that the efficiency of corrosion and scale inhibition of PESA and MEA-PESA is enhanced with the increase of degree of polymerization.

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