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Geochemical identification of a source rock affected by migrated hydrocarbons and its geological significance:Fengcheng Formation,southern Mahu Sag,Junggar Basin,NW china

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petroleum Science 2024年第1期21卷 100-114页

作者： Wen-Long Dang Gang Gao Xin-Cai You Ke-Ting Fan Jun Wu De-Wen Lei Wen-Jun He Yong Tang State Key Laboratory of petroleum Resource and Prospecting China University of Petroleum(Beijing)Beijing102249China School of GeoSciences China University of Petroleum(Beijing)Beijing102249China exploration&development institute Xinjiang Oil Field CompanyKaramay834000XinjiangChina

The Fengcheng Formation is a crucial source rock and the primary reservoir for oil accumulation in the Mahu Sag.Crude oils are distributed throughout the Fengcheng Formation,ranging from the edge to the interior of the sag in the southern Mahu Sag.These crude oils originate from in-situ source rocks in shallowly buried areas and the inner deep sag.During migration,the crude oil from the inner deep sag affects the source rocks close to carrier beds,leading to changes in the organic geochemical characteristics of the source rocks.These changes might alter source rock evaluations and oil-source correlation.Based on data such as total organic carbon(TOC),Rock-Eval pyrolysis of source rocks,and gas chromatography-mass spectrometry(GC-MS)of the saturated fraction,and considering the geological characteristics of the study area,we define the identification characteristics of source rock affected by migrated hydrocarbons and establish the various patterns of influence that migrated hydrocarbons have on the source rock of the Fengcheng Formation in the southern Mahu Sag.The source rocks of the Fengcheng Formation are mostly fair to good,containing mainly Type II organic matter and being thermally mature enough to generate oil.Source rocks affected by migrated hydrocarbons exhibit relatively high hydrocarbon contents(S1/TOC>110 mg HC/g TOC,Extract/TOC>30%,HC:hydrocarbon),relatively low Rock-Eval Tmax values,and relatively high tricyclic terpane contents with a descending and mountain-shaped distribution.Furthermore,biomarker composition parameters indicate a higher thermal maturity than in-situ source rocks.Through a comparison of the extract biomarker fingerprints of adjacent reservoirs and mudstones in different boreholes,three types of influence patterns of migrated hydrocarbons are identified:the edge-influence of thin sandstone-thick mudstone,the mixed-influence of sandstone-mudstone interbedded,and the full-influence of thick sandstone-thin mudstone.This finding reminds us that the influence of migrated hydrocarbons

关键词： Organic geochemistry Source rock Influence of migrated hydrocarbons Fengcheng Formation Southern Mahu Sag

A semi-analytical model for coupled flow in stress-sensitive multi-scale shale reservoirs with fractal characteristics

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petroleum Science 2024年第1期21卷 327-342页

作者： Qian Zhang Wen-Dong Wang Yu-Liang Su Wei Chen Zheng-Dong Lei Lei Li Yong-Mao Hao Key Laboratory of Unconventional Oil&Gas development(china University of petroleum(East china)) Ministry of EducationQingdao266580ShandongChina School of petroleum Engineering China University of Petroleum(East China)Qingdao266580ShandongChina Shale Oil development Branch Changqing Oilfield CompanyPetroChinaQingyang745708GansuChina Petrochina research institute of petroleum exploration&development Beijing100083China

A large number of nanopores and complex fracture structures in shale reservoirs results in multi-scale flow of oil. With the development of shale oil reservoirs, the permeability of multi-scale media undergoes changes due to stress sensitivity, which plays a crucial role in controlling pressure propagation and oil flow. This paper proposes a multi-scale coupled flow mathematical model of matrix nanopores, induced fractures, and hydraulic fractures. In this model, the micro-scale effects of shale oil flow in fractal nanopores, fractal induced fracture network, and stress sensitivity of multi-scale media are considered. We solved the model iteratively using Pedrosa transform, semi-analytic Segmented Bessel function, Laplace transform. The results of this model exhibit good agreement with the numerical solution and field production data, confirming the high accuracy of the model. As well, the influence of stress sensitivity on permeability, pressure and production is analyzed. It is shown that the permeability and production decrease significantly when induced fractures are weakly supported. Closed induced fractures can inhibit interporosity flow in the stimulated reservoir volume (SRV). It has been shown in sensitivity analysis that hydraulic fractures are beneficial to early production, and induced fractures in SRV are beneficial to middle production. The model can characterize multi-scale flow characteristics of shale oil, providing theoretical guidance for rapid productivity evaluation.

关键词： Multi-scale coupled flow Stress sensitivity Shale oil Micro-scale effect Fractal theory

Optimization of Gas-Flooding Fracturing development in Ultra-Low Permeability Reservoirs

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Fluid Dynamics & Materials Processing 2024年第3期20卷 595-607页

作者： Lifeng Liu Menghe Shi Jianhui Wang Wendong Wang Yuliang Su Xinyu Zhuang Tight Oil research institute PetroChina Research Institute of Petroleum Exploration&DevelopmentBeijing100083China Key Laboratory of Unconventional Oil&Gas development China University of Petroleum(East China)Qingdao266580China Oil&Gas Technology research institute Changqing Oilfield CompanyXi’an710018China

Ultra-low permeability reservoirs are characterized by small pore throats and poor physical properties, which areat the root of well-known problems related to injection and production. In this study, a gas injection floodingapproach is analyzed in the framework of numerical simulations. In particular, the sequence and timing of fracturechanneling and the related impact on production are considered for horizontal wells with different fracturemorphologies. Useful data and information are provided about the regulation of gas channeling and possible strategiesto delay gas channeling and optimize the gas injection volume and fracture parameters. It is shown that inorder to mitigate gas channeling and ensure high production, fracture length on the sides can be controlled andlonger fractures can be created in the middle by which full gas flooding is obtained at the fracture location in themiddle of the horizontal well. A Differential Evolution (DE) algorithm is provided by which the gas injectionvolume and the fracture parameters of gas injection flooding can be optimized. It is shown that an improvedoil recovery factor as high as 6% can be obtained.

关键词： Ultra-low permeability reservoir gas injection flooding component simulation fracture parameters intelligent optimization differential evolution

Modeling of multiphase flow in low permeability porous media:Effect of wettability and pore structure properties

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第4期16卷 1127-1139页

作者： Xiangjie Qin Yuxuan Xia Juncheng Qiao Jiaheng Chen Jianhui Zeng Jianchao Cai National Key Laboratory of petroleum Resources and Engineering China University of PetroleumBeijing102249China research institute of petroleum exploration and development Beijing10083China

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications.However,a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability.To address this issue,based on the digital rock of low permeability sandstone,a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process.In addition,a dual-porosity pore network model(PNM)is constructed to obtain the water-oil relative permeability of the sample.The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties.Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability.The injected water breaks through the outlet earlier with a large mass flow,while thick oil films exist in rough hydrophobic surfaces and poorly connected pores.The variation of water-oil relative permeability is significant,and residual oil saturation is high in the oil-wet system.The flooding is extensive,and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces;thus,water relative permeability is lower in the water-wet system.While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity.Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance,and a large microporosity corresponds to low residual oil saturation.This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

关键词： Low permeability porous media Water-oil flow Wettability Pore structures Dual porosity pore network model(PNM) Free surface model

Microscopic experiment on efficient construction of underground gas storages converted from water-invaded gas reservoirs

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petroleum exploration and development 2024年第1期51卷 203-212页

作者： JIANG Tongwen QI Huan WANG Zhengmao LI Yiqiang WANG Jinfang LIU Zheyu CAO Jinxin Petrochina Company Limited Beijing 100007China National Key Laboratory of petroleum Resources and Engineering China University of Petroleum(Beijing)Beijing 102249China College of petroleum Engineering China University of Petroleum(Beijing)Beijing 102249China Petrochina petroleum&New Energies Company Beijing 100007China Petrochina research institute of petroleum exploration&development Beijing 100083China

Based on the microfluidic technology,a microscopic visualization model was used to simulate the gas injection process in the initial construction stage and the bottom water invasion/gas injection process in the cyclical injection-production stage of the underground gas storage(UGS)rebuilt from water-invaded gas reservoirs.Through analysis of the gas-liquid contact stabilization mechanism,flow and occurrence,the optimal control method for lifecycle efficient operation of UGS was explored.The results show that in the initial construction stage of UGS,the action of gravity should be fully utilized by regulating the gas injection rate,so as to ensure the macroscopically stable migration of the gas-liquid contact,and greatly improve the gas sweeping capacity,providing a large pore space for gas storage in the subsequent cyclical injection-production stage.In the cyclical injection-production stage of UGS,a constant gas storage and production rate leads to a low pore space utilization.Gradually increasing the gas storage and production rate,that is,transitioning from small volume to large volume,can continuously break the hydraulic equilibrium of the remaining fluid in the porous media,which then expands the pore space and flow channels.This is conducive to the expansion of UGS capacity and efficiency for purpose of peak shaving and supply guarantee.

关键词： water-invaded gas-reservoir underground gas storage cyclical injection-production gas-water contact gas storage and production rate UGS capacity expansion control method

A regression approach for seismic first-break picking

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petroleum Science 2024年第3期21卷 1584-1596页

作者： Huan Yuan San-Yi Yuan Jie Wu Wen-Jing Sang Yu-He Zhao CNPC Key Laboratory of Geophysical exploration China University of Petroleum (Beijing) research institute of petroleum exploration & development—Northwest (NWGI) Key Laboratory of reservoir characterization of CNPCPetroChina

The picking efficiency of seismic first breaks(FBs) has been greatly accelerated by deep learning(DL)technology. However, the picking accuracy and efficiency of DL methods still face huge challenges in low signal-to-noise ratio(SNR) situations. To address this issue, we propose a regression approach to pick FBs based on bidirectional long short-term memory(Bi LSTM) neural network by learning the implicit Eikonal equation of 3D inhomogeneous media with rugged topography in the target region. We employ a regressive model that represents the relationships among the elevation of shots, offset and the elevation of receivers with their seismic traveltime to predict the unknown FBs, from common-shot gathers with sparsely distributed traces. Different from image segmentation methods which automatically extract image features and classify FBs from seismic data, the proposed method can learn the inner relationship between field geometry and FBs. In addition, the predicted results by the regressive model are continuous values of FBs rather than the discrete ones of the binary distribution. The picking results of synthetic data shows that the proposed method has low dependence on label data, and can obtain reliable and similar predicted results using two types of label data with large differences. The picking results of9380 shots for 3D seismic data generated by vibroseis indicate that the proposed method can still accurately predict FBs in low SNR data. The subsequent stacked profiles further illustrate the reliability and effectiveness of the proposed method. The results of model data and field seismic data demonstrate that the proposed regression method is a robust first-break picker with high potential for field application.

关键词： First-break picking Low signal-to-noise ratio Regression BiLSTM Traveltime Geometry Noisy seismic data

Effects of acid-rock reaction on physical properties during CO_(2)-rich industrial waste gas(CO_(2)-rich IWG)injection in shale reservoirs

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petroleum Science 2024年第1期21卷 272-285页

作者： Yi-Fan Wang Jing Wang Hui-Qing Liu Xiao-Cong Lv Ze-Min Ji National Key Laboratory of petroleum Resources and Engineering China University of PetroleumBeijing102249China MOE Key Laboratory of petroleum Engineering China University of PetroleumBeijing102249China research institute of exploration and development PetroChinaBeijing100083China

"Carbon peaking and carbon neutrality"is an essential national strategy,and the geological storage and utilization of CO_(2)is a hot issue today.However,due to the scarcity of pure CO_(2)gas sources in china and the high cost of CO_(2)capture,CO_(2)-rich industrial waste gas(CO_(2)-rich IWG)is gradually emerging into the public's gaze.CO_(2)has good adsorption properties on shale surfaces,but acidic gases can react with shale,so the mechanism of the CO_(2)-rich IWG-water-shale reaction and the change in reservoir properties will determine the stability of geological storage.Therefore,based on the mineral composition of the Longmaxi Formation shale,this study constructs a thermodynamic equilibrium model of water-rock reactions and simulates the regularity of reactions between CO_(2)-rich IWG and shale minerals.The results indicate that CO_(2)consumed 12%after reaction,and impurity gases in the CO_(2)-rich IWG can be dissolved entirely,thus demonstrating the feasibility of treating IWG through water-rock reactions.Since IWG inhibits the dissolution of CO_(2),the optimal composition of CO_(2)-rich IWG is 95%CO_(2)and 5%IWG when CO_(2)geological storage is the main goal.In contrast,when the main goal is the geological storage of total CO_(2)-rich IWG or impurity gas,the optimal CO_(2)-rich IWG composition is 50%CO_(2)and 50%IWG.In the CO_(2)-rich IWG-water-shale reaction,temperature has less influence on the water-rock reaction,while pressure is the most important parameter.SO2 has the greatest impact on water-rock reaction in gas.For minerals,clay minerals such as illite and montmorillonite had a significant effect on water-rock reaction.The overall reaction is dominated by precipitation and the volume of the rock skeleton has increased by 0.74 cm3,resulting in a decrease in shale porosity,which enhances the stability of CO_(2)geological storage to some extent.During the reaction between CO_(2)-rich IWG-water-shale at simulated temperatures and pressures,precipitation is the main reaction,and shale porosity decrease

关键词： CO_(2)-rich industrial waste gas Geological storage Acid-rock reaction Shale Geochemical modelling

The coupling control of biological precursors and environmental factors onβ-carotane enrichment in alkaline lacustrine source rocks:A case study from the Fengcheng formation in the western Junggar Basin,NW china

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petroleum Science 2024年第2期21卷 836-854页

作者： Mao-Guo Hou Ming Zha Hua Liu Hai-Lei Liu Jiang-Xiu Qu Ablimit Imin Xiu-Jian Ding Zhong-Fa Jiang School of Geosciences China University of PetroleumQingdaoShandong266580China research institute of exploration and development Xinjiang Petroleum Administration BureauKaramayXinjiang834000China

The organic-rich mudstones and dolostones of the Permian Fengcheng Formation(Fm.)are typically alkaline lacustrine source rocks,which are typified by impressively abundantβ-carotane.Abundantβ-carotane has been well acknowledged as an effective indicator of biological sources or depositional environments.However,the specific biological sources ofβ-carotane and the coupling control of biological sources and environmental factors on the enrichment ofβ-carotane in the Fengcheng Fm.remains obscure.Based on a comprehensive investigation of the bulk,molecular geochemistry,and organic petrology of sedimentary rocks and the biochemistry of phytoplankton in modern alkaline lakes,we proposed a new understanding of the biological precursors ofβ-carotane and elucidated the enrichment mechanism ofβ-carotane in the Fengcheng Fm.The results show that the biological precursors crucially control the enrichment ofβ-carotane in the Fengcheng Fm.The haloalkaliphilic cyanobacteria are the primary biological sources ofβ-carotane,which is suggested by a good positive correlation between the2-methylhopane index,7-+8-methyl heptadecanes/C_(max),C_(29%),andβ-carotane/C_(max)in sedimentary rocks and the predominance of cyanobacteria with abundantβ-carotene in modern alkaline lakes.The enrichment ofβ-carotane requires the reducing condition,and the paleoredox state that affects the enrichment ofβ-carotane appears to have a threshold.The paleoclimate conditions do not considerably impact the enrichment ofβ-carotane,but they have some influence on the water's paleosalinity by affecting evaporation and precipitation.While it does not directly affect the enrichment ofβ-carotane in the Fengcheng Fm.,paleosalinity does have an impact on the cyanobacterial precursor supply and the preservation conditions.

关键词： β-carotane enrichment Cyanobacterial input Environmental impact Alkaline lacustrine source rocks The Fengcheng formation

Machine learning for carbonate formation drilling: Mud loss prediction using seismic attributes and mud loss records

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petroleum Science 2024年第2期21卷 1241-1256页

作者： Hui-Wen Pang Han-Qing Wang Yi-Tian Xiao Yan Jin Yun-Hu Lu Yong-Dong Fan Zhen Nie National Key Laboratory of petroleum Resources and Engineering China University of Petroleum(Beijing)Beijing102249China College of Science China University of Petroleum-BeijingBeijing102249China petroleum exploration and Production research institute SINOPECBeijing102206China College of petroleum Engineering China University of Petroleum-BeijingBeijing102249China research institute of petroleum exploration and development CNPCBeijing100083China

Due to the complexity and variability of carbonate formation leakage zones, lost circulation prediction and control is one of the major challenges of carbonate drilling. It raises well-control risks and production expenses. This research utilizes the H oilfield as an example, employs seismic features to analyze mud loss prediction, and produces a complete set of pre-drilling mud loss prediction solutions. Firstly, 16seismic attributes are calculated based on the post-stack seismic data, and the mud loss rate per unit footage is specified. The sample set is constructed by extracting each attribute from the seismic trace surrounding 15 typical wells, with a ratio of 8:2 between the training set and the test set. With the calibration results for mud loss rate per unit footage, the nonlinear mapping relationship between seismic attributes and mud loss rate per unit size is established using the mixed density network model.Then, the influence of the number of sub-Gausses and the uncertainty coefficient on the model's prediction is evaluated. Finally, the model is used in conjunction with downhole drilling conditions to assess the risk of mud loss in various layers and along the wellbore trajectory. The study demonstrates that the mean relative errors of the model for training data and test data are 6.9% and 7.5%, respectively, and that R2is 90% and 88%, respectively, for training data and test data. The accuracy and efficacy of mud loss prediction may be greatly enhanced by combining 16 seismic attributes with the mud loss rate per unit footage and applying machine learning methods. The mud loss prediction model based on the MDN model can not only predict the mud loss rate but also objectively evaluate the prediction based on the quality of the data and the model.

关键词： Lost circulation Risk prediction Machine learning Seismic attributes Mud loss records