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A tectono-thermal perspective on the petroleum generation,accumulation and preservation in the southern Ordos Basin, North China

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petroleum Science 2024年第3期21卷 1459-1473页

作者： Peng Yang Zhan-Li Ren Jin-Hua Fu Hong-Ping Bao Hui Xiao Zheng Shi Kun Wang Yuan-Yuan Zhang Wen-Hui Liu Wen-Hou Li State Key Laboratory of Continental Dynamics Department of Geology Northwest University National Engineering Laboratory for exploration and Development of Low-Permeability Oil and Gas Fields Exploration and Development Research Institute of PetroChina Changqing Oilfield Company Shaanxi Key Lab of petroleum Accumulation Geology School of Earth Science and Engineering Xi'an Shiyou University Wuxi research institute of petroleum Geology Petroleum Exploration and Production Research InstituteSINOPEC

The southern Ordos Basin has excellent petroleum exploration prospects. However, the tectono-thermal history and the controls on petroleum generation, accumulation and preservation conditions in southern basin are unclear. In this study, we analyzed the present geothermal field, paleo-geothermal gradient,maturity of the hydrocarbon source rocks, uplift and cooling process and tectono-thermal evolution history. In the study area, for the Ordovician, Permain and the Triassic strata, the present temperature is low（30 70°C） in the southeastern area but high（80 140°C） in the northwestern area. The paleogeothermal gradient varied from 24°C/km to 30°C/km with a heat flow of 58—69 m W/m2（i.e., a medium-temperature basin）. The paleo-temperatures are higher than the present temperatures and the maximum paleo-temperatures controlled the thermal maturity of the source rocks. The vitrinite reflectance（Ro） values of the Triassic strata are >0.7% and the thermal maturity reached the middlemature oil generation stage. The Rovalues of the Permian-Ordovician strata are >1.8% and the thermal maturity reached the over-mature gas generation stage. The southern Ordos Basin has experienced the multiple tectonic events at the Late Ordovician Caledonian（452 Ma）, Late Triassic（215 Ma）, Late Jurassic（165 160 Ma）, End-Early Cretaceous（110 100 Ma） and Cenozoic（since 40 Ma）. A large-scale tectonothermal event occurred at the End-Early Cretaceous（110 100 Ma）, which was controlled by lithospheric extension, destruction and thinning. This event led to the highest paleo-temperatures and thermal maturities and coeval with the peak period of petroleum generation and accumulation. The southern Ordos Basin has undergone rapid and large-scale uplift since the Late Cretaceous due to expansion of the northeastern margin of the Tibetan Plateau, uplift of the Qinling orogenic belt and thrust faulting in the Liupanshan tectonic belt. The southern Ordos Basin experienced tectonic overprinting that was strong in the south and weak in the north. The strongest

关键词： Fission-track dating Vitrinite reflectance Geothermal field Tectono-thermal evolution petroleum geology Ordos Basin

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

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Identification of reservoir types in deep carbonates based on mixedkernel machine learning using geophysical logging data

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petroleum Science 2024年第3期21卷 1632-1648页

作者： Jin-Xiong Shi Xiang-Yuan Zhao Lian-Bo Zeng Yun-Zhao Zhang Zheng-Ping Zhu Shao-Qun Dong Key Laboratory of exploration Technologies for Oil and Gas Resources of the Ministry of Education Yangtze University School of Geosciences Yangtze University College of Geosciences China University of Petroleum (Beijing) petroleum exploration and production research institute of SINOPEC School of Earth Sciences and Engineering Xi'an Shiyou University

Identification of reservoir types in deep carbonates has always been a great challenge due to complex logging responses caused by the heterogeneous scale and distribution of storage spaces. Traditional cross-plot analysis and empirical formula methods for identifying reservoir types using geophysical logging data have high uncertainty and low efficiency, which cannot accurately reflect the nonlinear relationship between reservoir types and logging data. Recently, the kernel Fisher discriminant analysis(KFD), a kernel-based machine learning technique, attracts attention in many fields because of its strong nonlinear processing ability. However, the overall performance of KFD model may be limited as a single kernel function cannot simultaneously extrapolate and interpolate well, especially for highly complex data cases. To address this issue, in this study, a mixed kernel Fisher discriminant analysis(MKFD) model was established and applied to identify reservoir types of the deep Sinian carbonates in central Sichuan Basin, China. The MKFD model was trained and tested with 453 datasets from 7 coring wells, utilizing GR,CAL, DEN, AC, CNL and RT logs as input variables. The particle swarm optimization(PSO) was adopted for hyper-parameter optimization of MKFD model. To evaluate the model performance, prediction results of MKFD were compared with those of basic-kernel based KFD, RF and SVM models. Subsequently, the built MKFD model was applied in a blind well test, and a variable importance analysis was conducted. The comparison and blind test results demonstrated that MKFD outperformed traditional KFD, RF and SVM in the identification of reservoir types, which provided higher accuracy and stronger generalization. The MKFD can therefore be a reliable method for identifying reservoir types of deep carbonates.

关键词： Reservoir type identification Geophysical logging data Kernel Fisher discriminant analysis Mixed kernel function Deep carbonates

Supramolecular polymer-based gel fracturing fluid with a double network applied in ultra-deep hydraulic fracturing

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petroleum Science 2024年第3期21卷 1875-1888页

作者： Yong-Ping Huang Yong Hu Chang-Long Liu Yi-Ning Wu Chen-Wei Zou Li-Yuan Zhang Ming-Wei Zhao Cai-Li Dai School of petroleum Engineering China University of Petroleum(East China) Shandong Key Laboratory of Oilfield Chemistry China University of Petroleum(East China) SINOPEC petroleum exploration and production research institute CNOOC China Co Ltd Tianjin Branch

A gel based on polyacrylamide, exhibiting delayed crosslinking characteristics, emerges as the preferred solution for mitigating degradation under conditions of high temperature and extended shear in ultralong wellbores. High viscosity/viscoelasticity of the fracturing fluid was required to maintain excellent proppant suspension properties before gelling. Taking into account both the cost and the potential damage to reservoirs, polymers with lower concentrations and molecular weights are generally preferred. In this work, the supramolecular action was integrated into the polymer, resulting in significant increases in the viscosity and viscoelasticity of the synthesized supramolecular polymer system.The double network gel, which is formed by the combination of the supramolecular polymer system and a small quantity of Zr-crosslinker, effectively resists temperature while minimizing permeability damage to the reservoir. The results indicate that the supramolecular polymer system with a molecular weight of(268—380) × 10～4g/mol can achieve the same viscosity and viscoelasticity at 0.4 wt% due to the supramolecular interaction between polymers, compared to the 0.6 wt% traditional polymer(hydrolyzed polyacrylamide, molecular weight of 1078 × 10～4g/mol). The supramolecular polymer system possessed excellent proppant suspension properties with a 0.55 cm/min sedimentation rate at 0.4 wt%, whereas the0.6 wt% traditional polymer had a rate of 0.57 cm/min. In comparison to the traditional gel with a Zrcrosslinker concentration of 0.6 wt% and an elastic modulus of 7.77 Pa, the double network gel with a higher elastic modulus(9.00 Pa) could be formed only at 0.1 wt% Zr-crosslinker, which greatly reduced the amount of residue of the fluid after gel-breaking. The viscosity of the double network gel was66 m Pa s after 2 h shearing, whereas the traditional gel only reached 27 m Pa s.

关键词： Ultra-deep reservoir Gel fracturing fluid Double network Supramolecular polymer system Proppant suspension property

Differences in and factors controlling organic matter enrichment in the Ziliujing Formation shale in the Sichuan Basin

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petroleum Science 2024年第1期21卷 77-86页

作者： Peng Li Zhong-Bao Liu He Bi Tao Jiang Rui-Kang Bian Peng-Wei Wang Xiao-Yu Shang State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development Beijing102206China Key Laboratory of Shale Oil/Gas exploration and production Technology SINOPECBeijing102206China petroleum exploration and production research institute SINOPECBeijing102206China research institute of petroleum exploration and Development PetroChinaBeijing100083China Chinese Academy of Geological Sciences Beijing100037China No.4 Oil production Plant in Daqing Oilfield Co Ltd. Daqing163511HeilongjiangChina

Lacustrine shale oil and gas are important fields for unconventional exploration and development in China,and organic-rich shale deposition lays down the critical foundation for hydrocarbon generation.There are two sets of shale,the Dongyuemiao and Da’anzhai Members,in the Ziliujing Formation in the Sichuan Basin.To identify the differential enrichment characteristics of organic matter and clarify its controlling factors,geochemical analyses of organic and inorganic geochemical analyses were performed.The results showed that the total organic carbon content of the Dongyuemiao shale(1.36%)is slightly higher than that of the Da’anzhai shale(0.95%).The enrichment of organic matter in the two shales resulted from the comprehensive controls of paleoproductivity,paleoenvironment,and terrigenous input,but different factors have different effects.In addition,driven by climate,the change in the sulfate concentration in the bottom water further led to the different intensities of bacterial sulfate reduction in early diagenesis.This made a great difference regarding organic matter accumulation in the two members.In general,climate may have played a dominant role in organic matter enrichment in the two sets of shale.

关键词： Lacustrine shale Ziliujing Formation Sichuan Basin Enrichment mechanism of organic matter

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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

An improved deep dilated convolutional neural network for seismic facies interpretation

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petroleum Science 2024年第3期21卷 1569-1583页

作者： Na-Xia Yang Guo-Fa Li Ting-Hui Li Dong-Feng Zhao Wei-Wei Gu State Key Laboratory of petroleum Resources and Engineering CNPC Key Lab of Geophysical Exploration China University of Petroleum (Beijing) Dagang Branch Research InstituteBGP

With the successful application and breakthrough of deep learning technology in image segmentation,there has been continuous development in the field of seismic facies interpretation using convolutional neural networks. These intelligent and automated methods significantly reduce manual labor, particularly in the laborious task of manually labeling seismic facies. However, the extensive demand for training data imposes limitations on their wider application. To overcome this challenge, we adopt the UNet architecture as the foundational network structure for seismic facies classification, which has demonstrated effective segmentation results even with small-sample training data. Additionally, we integrate spatial pyramid pooling and dilated convolution modules into the network architecture to enhance the perception of spatial information across a broader range. The seismic facies classification test on the public data from the F3 block verifies the superior performance of our proposed improved network structure in delineating seismic facies boundaries. Comparative analysis against the traditional UNet model reveals that our method achieves more accurate predictive classification results, as evidenced by various evaluation metrics for image segmentation. Obviously, the classification accuracy reaches an impressive 96%. Furthermore, the results of seismic facies classification in the seismic slice dimension provide further confirmation of the superior performance of our proposed method, which accurately defines the range of different seismic facies. This approach holds significant potential for analyzing geological patterns and extracting valuable depositional information.

关键词： Seismic facies interpretation Dilated convolution Spatial pyramid pooling Internal feature maps Compound loss function

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

Impact of effective stress on permeability for carbonate fractured-vuggy rocks

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 942-960页

作者： Ke Sun Huiqing Liu Juliana Y.Leung Jing Wang Yabin Feng Renjie Liu Zhijiang Kang Yun Zhang State Key Laboratory of petroleum Resources and Prospecting China University of PetroleumBeijing102249China School of Mining&petroleum Engineering University of AlbertaEdmontonT6G 1H9Canada SINOPEC petroleum exploration and production research institute Beijing100083China

To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs,several core models with different structural characteristics were designed and fabricated to investigate the impact of effective stress on permeability for carbonate fractured-vuggy rocks(CFVR).It shows that the permeability performance curves under different pore and confining pressures(i.***.altered stress conditions)for the fractured core models and the vuggy core models have similar change patterns.The ranges of permeability variation are significantly wider at high pore pressures,indicating that permeability reduction is the most significant during the early stage of development for fractured-vuggy reservoirs.Since each obtained effective stress coefficient for permeability(ESCP)varies with the changes in confining pressure and pore pressure,the effective stresses for permeability of four representative CFVR show obvious nonlinear characteristics,and the variation ranges of ESCP are all between 0 and 1.Meanwhile,a comprehensive ESCP mathematical model considering triple media,including matrix pores,fractures,and dissolved vugs,was proposed.It is proved theoretically that the ESCP of CFVR generally varies between 0 and 1.Additionally,the regression results showed that the power model ranked highest among the four empirical models mainly applied in stress sensitivity characterization,followed by the logarithmic model,exponential model,and binomial model.The concept of“permeability decline rate”was introduced to better evaluate the stress sensitivity performance for CFVR,in which the one-fracture rock is the strongest,followed by the fracture-vug rock and two-horizontalfracture rock;the through-hole rock is the weakest.In general,this study provides a theoretical basis to guide the design of development and adjustment programs for carbonate fractured-vuggy reservoirs.

关键词： Effective stress Permeability Carbonate fractured-vuggy rocks Structure characteristics Stress sensitivity