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A new interacting capillary bundle model on the multiphase flow in micropores of tight rocks

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petroleum Science 2024年第2期21卷 1099-1112页

作者： Wen-Quan Deng Tian-Bo Liang Wen-Zhong Wang Hao Liu Jun-Lin Wu Fu-Jian Zhou National key laboratory of petroleum resources and Engineering China University of Petroleum(Beijing)Beijing102249China

Surfactants are widely used in the fracturing fluid to enhance the imbibition and thus the oil recovery rate. However, current numerical models cannot capture the physics behind capillary imbibition during the wettability alteration by surfactants. Although the interacting capillary bundle(ICB) model shows potential in characterizing imbibition rates in different pores during wettability alteration, the existing ICB models neglect the influence of wettability and viscosity ratio on the imbibition behavior, making it difficult to accurately describe the oil-water imbibition behavior within the porous media. In this work,a new ICB mathematical model is established by introducing pressure balance without assuming the position of the leading front to comprehensively describe the imbibition behavior in a porous medium under different conditions, including gas-liquid spontaneous imbibition and oil-water *** the pore size distribution of a tight rock is known, this new model can predict the changes of water saturation during the displacement process in the tight rock, and also determine the imbibition rate in pores of different sizes. The water saturation profiles obtained from the new model are validated against the waterflooding simulation results from the CMG, while the imbibition rates calculated by the model are validated against the experimental observations of gas-liquid spontaneous imbibition. The good match above indicates the newly proposed model can show the water saturation profile at a macroscopic scale while capture the underlying physics of the multiphase flow in a porous medium at a microscopic scale. Simulation results obtained from this model indicate that both wettability and viscosity ratio can affect the sequence of fluid imbibition into pores of different sizes during the multiphase flow, where less-viscous wetting fluid is preferentially imbibed into larger pores while more-viscous wetting fluid tends to be imbibed into smaller pores. Fur

关键词： Imbibition Multiphase flow Tight rock Interacting capillary bundle model Wettability

Integrated classification method of tight sandstone reservoir based on principal component analysise simulated annealing genetic algorithmefuzzy cluster means

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petroleum Science 2023年第5期20卷 2747-2758页

作者： Bo-Han Wu Ran-Hong Xie Li-Zhi Xiao Jiang-Feng Guo Guo-Wen Jin Jian-Wei Fu National key laboratory of petroleum resources and Engineering China University of Petroleum(Beijing)Beijing102249China

In this research,an integrated classification method based on principal component analysis-simulated annealing genetic algorithm-fuzzy cluster means(PCA-SAGA-FCM)was proposed for the unsupervised classification of tight sandstone reservoirs which lack the prior information and core experiments.A variety of evaluation parameters were selected,including lithology characteristic parameters,poro-permeability quality characteristic parameters,engineering quality characteristic parameters,and pore structure characteristic *** PCA was used to reduce the dimension of the evaluation pa-rameters,and the low-dimensional data was used as *** unsupervised reservoir classification of tight sandstone reservoir was carried out by the SAGA-FCM,the characteristics of reservoir at different categories were analyzed and compared with the lithological *** analysis results of numerical simulation and actual logging data show that:1)compared with FCM algorithm,SAGA-FCM has stronger stability and higher accuracy;2)the proposed method can cluster the reservoir flexibly and effectively according to the degree of membership;3)the results of reservoir integrated classification match well with the lithologic profle,which demonstrates the reliability of the classification method.

关键词： Tight sandstone Integrated reservoir classification Principal component analysis Simulated annealing genetic algorithm Fuzzy cluster means

Probing the oil content in oil shale with terahertz spectroscopy

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Science China(Physics,Mechanics & Astronomy) 2015年第11期58卷 121-122页

作者： BAO RiMa LI YiZhang ZHAN HongLei ZHAO Kun WANG Wei MA Yue WU JianXun LIU ShaoHua LI ShuYuan XIAO LiZhi State key laboratory of petroleum resources and Prospecting China University of Petroleum Beijing key laboratory of Optical Detection Technology for Oil and Gas China University of Petroleum

Dear Editors, The merit of coal has been recognized by average people, whereas the value of oil shale has not been realized even by some experts in energy field. Compared to coal, oil shale also has dark looks and giant reserves while the content of ash in oil shale is higher. Owing to organic matter it con- tains, a sort of fuel named shale oil can be extracted via pyrolysis, which resembles crude oil in composition and can be further processed to obtain gas and diesel .

关键词：科学学科学知识物理学力学天文学

A new method for fluid identification and saturation calculation of low contrast tight sandstone reservoir

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petroleum Science 2024年第5期21卷 3189-3201页

作者： Shuai Wang Ran-Hong Xie Guo-Wen Jin Jiang-Feng Guo Li-Zhi Xiao State key laboratory of petroleum resources and Engineering China University of Petroleum(Beijing)Beijing102249China

The resistivity difference between oil and gas layers and the water layers in low contrast tight sandstone reservoirs is subtle. Fluid identification and saturation calculation based on conventional logging methods are facing challenges in such reservoirs. In this paper, a new method is proposed for fluid identification and saturation calculation in low contrast tight sandstone reservoirs. First, a model for calculating apparent formation water resistivity is constructed, which takes into account the influence of shale on the resistivity calculation and avoids apparent formation water resistivity abnormal *** on the distribution of the apparent formation water resistivity obtained by the new model, the water spectrum is determined for fluid identification in low contrast tight sandstone *** this, according to the average, standard deviation, and endpoints of the water spectrum, a new four-parameter model for calculating reservoir oil and gas saturation is built. The methods proposed in this paper are applied to the low contrast tight sandstone reservoirs in the Q4 formation of the X53 block and X70 block in the south of Songliao Basin, China. The results show that the water spectrum method can effectively distinguish oil-water layers and water layers in the study area. The standard deviation of the water spectrum in the oil-water layer is generally greater than that in the water layer. The new four-parameter model yields more accurate oil and gas saturation. These findings verify the effectiveness of the proposed methods.

关键词： Low contrast reservoirs Fluid identification Saturation calculation Water spectrum method Conventional logging

Identification of low-resistivity-low-contrast pay zones in the feature space with a multi-layer perceptron based on conventional well log data

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petroleum Science 2022年第2期19卷 570-580页

作者： Lun Gao Ran-Hong Xie Li-Zhi Xiao Shuai Wang Chen-Yu Xu State key laboratory of petroleum resources and Prospecting China University of Petroleum(Beijing)Beijing102249China

In the early exploration of many oilfields,low-resistivity-low-contrast(LRLC)pay zones are easily overlooked due to the resistivity similarity to the water *** identification methods are model-driven and cannot yield satisfactory results when the causes of LRLC pay zones are *** this study,after analyzing a large number of core samples,main causes of LRLC pay zones in the study area are discerned,which include complex distribution of formation water salinity,high irreducible water saturation due to micropores,and high shale ***,different oil testing layers may have different causes of LRLC pay *** a result,in addition to the well log data of oil testing layers,well log data of adjacent shale layers are also added to the original dataset as reference *** densitybased spatial clustering algorithm with noise(DBSCAN)is used to cluster the original dataset into 49 clusters.A new dataset is ultimately projected into a feature space with 49 *** new dataset and oil testing results are respectively treated as input and output to train the multi-layer perceptron(MLP).A total of 3192 samples are used for stratified 8-fold cross-validation,and the accuracy of the MLP is found to be 85.53%.

关键词： Low-resistivity-low-contrast(LRLC)pay zones Conventional well logging Machine learning DBSCAN algorithm Multi-layer perceptron

Visualization of hydraulic fracture interacting with pre-existing fracture

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petroleum Science 2023年第6期20卷 3723-3735页

作者： Zi-Xiao Xie Xiao-Guang Wu Teng-Da Long Zhong-Wei Huang Gen-Sheng Li Wen-Chao Zou Zhao-Wei Sun State key laboratory of petroleum resources and Prospecting China University of Petroleum-BeijingBeijing102249China

Hydraulic fracturing is considered the main stimulation method to develop shale gas reservoirs. Due to its strong heterogeneity, the shale gas formation is typically embedded with geological discontinuities such as bedding planes and natural fractures. Many researchers realized that the interaction between natural fractures and hydraulic fractures plays a crucial role in generating a complex fracture network. In this paper, true tri-axial hydraulic fracturing tests were performed on polymethyl methacrylate (PMMA), on which pre-existing fracture was pre-manufactured to simulate natural fracture. A cohesive model has been developed to verify the results of the experimental tests. The key findings demonstrate that the experimental results agreed well with the numerical simulation outcomes where three main interaction modes were observed: crossing;being arrested by opening the pre-existing fracture;being arrested without dilating the pre-existing fracture. Crossing behavior is more likely to occur with the approaching angle, horizontal stress difference, and injection rate increase. Furthermore, the higher flow rate might assist in reactivating the natural fractures where both sides of the pre-existing fractures were reactivated as the injection rate increased from 5 to 20 mL/min. Additionally, hydraulic fractures show a tendency to extend vertically rather than along the direction of maximum horizontal stress when they are first terminated at the interface. This research may contribute to the field application of hydraulic fracturing in shale gas formation.

关键词： Hydraulic fracturing Natural fracture Fracture propagation Interaction mode PMMA

Oilfield analogy and productivity prediction based on machine learning: Field cases in PL oilfield, China

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petroleum Science 2024年第4期21卷 2554-2570页

作者： Wen-Peng Bai Shi-Qing Cheng Xin-Yang Guo Yang Wang Qiao Guo Chao-Dong Tan State key laboratory of petroleum resources and Engineering China University of Petroleum(Beijing)Beijing102249China

In the early time of oilfield development, insufficient production data and unclear understanding of oil production presented a challenge to reservoir engineers in devising effective development plans. To address this challenge, this study proposes a method using data mining technology to search for similar oil fields and predict well productivity. A query system of 135 analogy parameters is established based on geological and reservoir engineering research, and the weight values of these parameters are calculated using a data algorithm to establish an analogy system. The fuzzy matter-element algorithm is then used to calculate the similarity between oil fields, with fields having similarity greater than 70% identified as similar oil fields. Using similar oil fields as sample data, 8 important factors affecting well productivity are identified using the Pearson coefficient and mean decrease impurity(MDI) method. To establish productivity prediction models, linear regression(LR), random forest regression(RF), support vector regression(SVR), backpropagation(BP), extreme gradient boosting(XGBoost), and light gradient boosting machine(Light GBM) algorithms are used. Their performance is evaluated using the coefficient of determination(R^(2)), explained variance score(EV), mean squared error(MSE), and mean absolute error(MAE) metrics. The Light GBM model is selected to predict the productivity of 30 wells in the PL field with an average error of only 6.31%, which significantly improves the accuracy of the productivity prediction and meets the application requirements in the field. Finally, a software platform integrating data query,oil field analogy, productivity prediction, and knowledge base is established to identify patterns in massive reservoir development data and provide valuable technical references for new reservoir development.

关键词： Data mining technique Analogy parameters Oilfield analogy Productivity prediction Software platform

Pressure transient characteristics of non-uniform conductivity fractured wells in viscoelasticity polymer flooding based on oil-water two-phase flow

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petroleum Science 2024年第1期21卷 343-351页

作者： Yang Wang Jia Zhang Shi-Long Yang Ze-Xuan Xu Shi-Qing Cheng National key laboratory of petroleum resources and Engineering China University of Petroleum(Beijing)Beijing102249China

Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil *** contrast to water,polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinning and shear thickening,polymer convection,diffusion,adsorption retention,inaccessible pore volume and reduced effective ***,the flux density and fracture conductivity along the hydraulic fracture are generally non-uniform due to the effects of pressure distribution,formation damage,and proppant *** this paper,we present an oil-water two-phase flow model that captures these complex non-Newtonian and nonlinear behavior,and non-uniform fracture characteristics in fractured polymer *** hydraulic fracture is firstly divided into two parts:high-conductivity fracture near the wellbore and low-conductivity fracture in the far-wellbore section.A hybrid grid system,including perpendicular bisection(PEBI)and Cartesian grid,is applied to discrete the partial differential flow equations,and the local grid refinement method is applied in the near-wellbore region to accurately calculate the pressure distribution and shear rate of polymer *** combination of polymer behavior characterizations and numerical flow simulations are applied,resulting in the calculation for the distribution of water saturation,polymer concentration and reservoir *** with the polymer flooding well with uniform fracture conductivity,this non-uniform fracture conductivity model exhibits the larger pressure difference,and the shorter bilinear flow period due to the decrease of fracture flow ability in the far-wellbore *** field case of the fall-off test demonstrates that the proposed method characterizes fracture characteristics more accurately,and yields fracture half-lengths that better match engineering reality,enabling a quantitative segmented characterization of the near-wellbore section with high fracture conductivity and th

关键词： Polymer flooding Non-Newtonian fluid Non-uniform fracture conductivity Two-phase flow Pressure transient analysis

Rock mechanical properties of coal in cryogenic condition

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petroleum Science 2023年第1期20卷 407-423页

作者： Hai-Tao Wen Rui-Yue Yang Mei-Yang Jing Zhong-Wei Huang Chun-Yang Hong Jian-Xiang Chen Ri-Chao Cong State key laboratory of petroleum resources and Prospecting China University of Petroleum(Beijing)Beijing102249China

Liquid nitrogen(LN2)fracturing is a kind of non-aqueous fracturing technology,which is expected to provide a new and efficient way for coalbed methane(CBM)*** mechanical properties of coal under LN_(2) freezing are very important for studying the mechanism of LN2 ***,most of the current research is limited to studying mechanical properties of rocks after being frozen by LN2 and returned to room *** this paper,the effect of LN2 freezing on the mechanical properties of coal was *** strength tests and Brazil tests were carried out for dry and water-saturated coal samples with different types and bedding *** addition,standard electron microscopy(standard SEM)and cryo-electron microscopy(Cryo-SEM)were used to compare the fracture morphology of coal samples at room temperature and LN_(2) *** results showed that LN_(2) freezing can damage and improve the mechanical properties of coal *** strength of saturated coal under freezing is higher than that of dry coal,and the filling of ice can enhance the mechanical strength of *** addition,the mechanical properties of coal with higher porosity are enhanced more than that of coal with lower porosity under LN_(2) *** main findings of this study are the keys to the research of LN_(2) fracturing mechanisms in CBM reservoirs.

关键词： Liquid nitrogen freezing Mechanical properties Damage and strengthening Coal