Lithologic Reservoirs

There are some problems in unconventional hydrocarbon enrichment research,such as unclear key controlling factors,unclear enrichment mechanism and efficiency. By means of investigation,field observation, core description,microscopic identification,simulation experiment and statistical analysis,combined with its own research outcome,this paper proposed the hypothesis of "fracture-pore coupling enriching hydrocarbon" based on the knowledge of fracture-pore coupling is the key controlling factor restricting unconventional oil and gas retention,migration,accumulation and enrichment. The main conclusions are as follows:(1)Fracture-pore coupling not only controls the dynamic and resistance of unconventional hydrocarbon migration,accumulation and enrichment,but also controls their migration channels and accumulation space,as well as their phase, mode,fluid flow rule and efficiency of migration and accumulation.(2)There are 16 kinds of fracture-pore coupling and four evaluation levels of fracture-pore coupling of advantage coupling,good coupling,general coupling and unfavorable coupling,and fracture-pore system with advantage coupling is most conducive to the migration,accumulation and enrichment of unconventional oil and gas,followed by that with good coupling.(3)This paper summarized the background,basic principle,main basis,main viewpoints of the "fracture-pore coupling enriching hydrocarbon hypothesis", and exploration strategy based on this hypothesis. This hypothesis has important guiding significance for unconventional oil and gas exploration,but it still needs further revision,improvement and development to develop the unconventional oil and gas accumulation theory.

PETROLEUM GEOLOGY

Stratigraphic division and sedimentary evolution characteristics of Lower Cambrian in the southern margin of Ordos Basin

WANG Hongbo, GUO Wei, ZHANG Guisong, JING Xianghui, LI Xiangbo, WANG Jing

2019, Vol.31(4): 13–20 Abstract ( 432 ) PDF (3731 KB) ( 424 )

doi: https://doi.org/10.12108/yxyqc.20190402

In order to study the stratigraphic development and sedimentary evolution of Lower Cambrian in the southern margin of Ordos Basin,geotectonic background,stratigraphic correlation and lithofacies palaeogeography were studied. The results show that:(1)Dongpo Formation and Luoquan Formation are the main source rocks developed under Xinji Formation in the southern margin of Ordos Basin,which can be classified into Lower Cambrian. The TOC mass fraction is 0.19%-11.18%,with an average of 3.14%,so they are the best source rocks of Cambrian.(2)The entire North China region transgressed in the early Early Cambrian and deposited a set of transgression strata. The southern margin of Ordos Basin underwent deep-water bay deposition,coastal deposition and carbonate gentle slope deposition.(3)The sedimentary thickness of Cambrian in the southern margin of Ordos Basin is 500-1 300 m,and it can reach more than 1 500 m locally. The oolitic shoals of Zhangxia Formation are widely distributed,with dissolved pores and intergranular pores developed. They are relatively high-quality reservoirs and form a good source-reservoir assemblage with Dongpo Formation and Luoquan Formation. The research results are of great significance to the Cambrian oil and gas exploration in Ordos Basin.

Hydrocarbon charging time of Chang 8 reservoir of Yanchang Formation in southern Ordos Basin

DING Chao, GUO Shun, GUO Lan, GUO Xiaobo, DU Guichao, WU Hongshuai

2019, Vol.31(4): 21–31 Abstract ( 319 ) PDF (7574 KB) ( 431 )

doi: https://doi.org/10.12108/yxyqc.20190403

In order to determine hydrocarbon charging time of Chang 8 reservoir of Yanchang Formation in southern Ordos Basin,the diagenetic evolution sequence of sand reservoir and homogenization temperature of fluid inclusion(FI)analysis were carried out. The results show that:(1)the Chang 8 reservoir show three stages of geochronology of hydrocarbon charging,the first stage of hydrocarbon FI that show brine inclusions are mainly hosted early fracture and dissolution area of quartz,and the homogenization temperature of associated brine inclusions is in the range from 61.1℃ to 121.7℃. The second stage of hydrocarbon FI that show brine inclusions are mainly hosted quartz overgrowths and calcite cement,and the homogenization temperature of associated brine inclusions is in the range from 106.2℃ to 155.7℃. The third stage of hydrocarbon FI that show brine inclusions are mainly hosted late fractures cutting through quartz and its overgrowths,and the homogenization temperature of associated brine inclusions is in the range from 92.2℃ to 130.5℃.(2)Combining with the tectonic thermal evolution history of the study area,it can be concluded that the first hydrocarbon charging stage is early oil-gas accumulation processes from Early Jurassic to Late Jurassic(192.5-152.0 Ma),the second stage is key processes of hydrocarbon occurred from Late Jurassic to Early Cretaceous(152.0-126.0 Ma),and the third stage is processes of adjustment and accumulation of hydrocarbon occurred in Paleogene(60.0-36.5 Ma). The study results is of great significance to secondary hydrocarbon reservoir exploration in southern Ordos Basin.

Reservoir-controlling effect of basement faults and favorable exploration zones in southwestern Qaidam Basin

NI Xianglong, WANG Jiangong, GUO Jiajia, DU Binshan, YI Dinghong, LONG Guohui, LI Zhiming, HUI Yuanyuan

2019, Vol.31(4): 32–41 Abstract ( 282 ) PDF (7576 KB) ( 330 )

doi: https://doi.org/10.12108/yxyqc.20190404

In recent years,great breakthroughs have been made in hydrocarbon exploration of basement rock in southwestern Qaidam Basin,and Kunbei reservoir has been found. In order to make clear the reservoir-controlling effect and accumulation model of basement faults,drilling core analysis,logging analysis and 3-D seismic data interpretation were carried out. The results show that:(1)Deep and large faults were well developed and they controlled the development of basement reservoir. The early activities of synsedimentary reverse faults No. Ⅺ and Ⅷ and Alar fault controlled the development of the three major hydrocarbon-generating sags. The deep and large faults in the basement were active during the key reservoir-forming periods,providing vertical migration channel for the initial hydrocarbon accumulation.(2)The paleo-uplift controlled by deep and large faults was an advantage area for oil and gas accumulation,and fracture and dissolved pores developed in weathering crust provided reservoir space for oil and gas accumulation.(3)Capping capacity of mudstone caprock overlying on weathering crust controlled oil and gas enrichment,and the late activity of deep and large faults may destroy the capping capacity.(4)An oil and gas accumulation model for basement reservoir with deep and large faults as the core was established,namely,deep and large faults adjacent to hydrocarbon-generating sags,paleotectonic setting and highquality mudstone caprock jointly controlled hydrocarbon enrichment and accumulation.(5)Zhaxi nose-shaped uplift,Wunan nose-shaped uplift and Q3 nose-shaped paleo-uplift in Yuejin slope located on the hanging wall of deep and large faults are favorable areas for the next exploration in this area. The study results have guiding significance for basement reservoir exploration in Qaidam Basin.

Characteristics of clay minerals and its impacts on reservoir quality of tight sandstone gas reservoir: a case from Sulige Gas Field,Ordos Basin

REN Dazhong, ZHOU Zhaohua, LIANG Ruixiang, ZHOU Ran, LIU Na, NAN Junxiang

2019, Vol.31(4): 42–53 Abstract ( 501 ) PDF (5598 KB) ( 397 )

doi: https://doi.org/10.12108/yxyqc.20190405

In order to study the reservoir properties of tight sandstone gas reservoirs,based on quantitative evaluation of clay mineral occurrence by X-ray diffraction,combined with the data of thin sections(TS),scanning electron microscopy(SEM),pressure-controlled mercury intrusion(PCMI)and nuclear magnetic resonance (NMR),physical properties,pore structure and factors affecting movable fluids were studied on 15 clay mineral samples from tight sandstone gas reservoir of the Permian He 8 member in Sulige Gas Field,Ordos Basin. The results show that illite(3.07%)and kaolinite(1.86%)are typical clay mineral in the study area. The clay minerals could provide abundant pore space and were the indirect evidence of the appearance of dissolved pores. Chlorite filled the pores,and a large number of illite and I/S mixed layer would also deteriorate reservoir properties. Movable fluid parameters took the hydrophilic minerals on the pore surface into account,highlighting the relationship between hydrophilic clay and occurrence characteristics of movable fluid(R2>0.70). This research provides insights into studying the coupling relationship between clay minerals and reservoir quality and theoretical basis and practical guidance for the gas production.

An improved method for evaluating rock brittleness index based on stress-strain curve characteristics

CAO Qian, QI Minghui, ZHANG Haotian, HUANG Yi, ZHANG Yeyu

2019, Vol.31(4): 54–61 Abstract ( 276 ) PDF (1904 KB) ( 584 )

doi: https://doi.org/10.12108/yxyqc.20190406

As one of the important indexes for rock mechanics evaluation,the evaluation of brittleness index is of great significance to rock characteristics. 21 rock samples of the fifth member of Xujiahe Formation of Xinchang Gas Field in Sichuan Basin were selected to carry out laboratory triaxial rock mechanics experiments. Triaxial saturation hydraulics and acoustic tests of samples under confining pressure of 0 MPa,12 MPa,22 MPa and 32 MPa were simulated respectively. Based on the stress-strain curve characteristics,the differences of different brittleness characteristic parameters were analyzed. The brittleness factors such as BYm,Bμ,BRε and BRσ respectively based on Young's modulus,Poisson's ratio,recoverable strain and total strain,and yield strength and compressive strength,were calculated. The existing brittleness evaluation methods based on stress-strain curves were compared and analyzed,and the functional relationships of brittleness index Bn with BYm,Bμ,BRε and BRσ were established according to the laboratory rock mechanics test results. A new brittleness index model was established by multiple regression method to evaluate the brittleness of rock samples. The results show that the conventional brittleness index evaluation method is not effective in distinguishing brittleness of rock samples,and the improved model can better distinguish high brittle mudstone,low brittle mudstone and sandstone in the study area. The study results have guiding significance for accurately evaluating the brittleness characteristics of rocks.

Mineral compositions and brittleness evaluation of shale of Niutitang Formation in northern Guizhou

YE Yapei, TANG Shuheng, XI Zhaodong, ZHANG Yaoxuan

2019, Vol.31(4): 62–71 Abstract ( 370 ) PDF (10366 KB) ( 408 )

doi: https://doi.org/10.12108/yxyqc.20190407

In order to study mineral composition characteristics and genesis of the shale of Lower Cambrian Niutitang Formation in northern Guizhou,and propose a new method of shale brittleness evaluation for this area, the mineral compositions of Niutitang Formation shale in XY1 well in northern Guizhou were studied by means of thin section identification,scanning electron microscopy-energy spectrum analysis,cathodoluminescence,element scanning analysis,mineral quantitative X-ray diffraction analysis and triaxial compression test,and brittleness characteristics of shale were evaluated based on petrophysics and mineral composition. The results show that the minerals of Niutitang Formation mainly consist of quartz and clay minerals,and also contain a small amount of feldspar,carbonate minerals and pyrite,with volume fractions of 43.5%,30.3%,11.6%,8.3% and 6.2%,respectively. By analyzing the relationships of mineral content with elastic modulus and Poisson's ratio,it is considered that the lower part of Niutitang Formation is more brittle than the upper part,and the brittle minerals are composed of quartz,pyrite and carbonate minerals,with the volume fraction of brittle minerals of 41.7%-82.3%. The difference of sedimentary environment is one of the reasons for the difference in rock brittleness.

Elemental geochemical characteristics and main controlling factors of organic matter enrichment of Longmaxi Formation in southern Sichuan

GAO Qiao, WANG Xingzhi, ZHU Yiqing, ZHAO Shengxian, ZHANG Rui, XIAO Zheyu

2019, Vol.31(4): 72–84 Abstract ( 353 ) PDF (4397 KB) ( 549 )

doi: https://doi.org/10.12108/yxyqc.20190408

In order to clarify the paleoredox conditions and the main controlling factors of organic matter enrichment of Longmaxi Formation in Weiyuan-Changing areas,southern Sichuan,the analysis of major and trace elements in four coring wells was carried out. The results show that:(1)Long 11 sub-member of Longmaxi Formation is rich in elements of V,Ni,Ba,Th and U with the loss of Cr element,while the Long 12 sub-member is rich in elements of V,Ba,Th and U with the loss of Cr and Co elements.(2)In the early sedimentary stage of Long 11 sub-member,the study area was in anoxic environment,and in the middle and late sedimentary stages, the redox condition evolved into dysoxic or oxic in Weiyuan area,while the environment evolved into oxic in Changning area.(3)In the sedimentary stage of Long 12 sub-member,WD204 H well area was steadily in oxic condition and WD201 well area was still in dysoxic or partially oxic condition in Weiyuan area,while the condition was entirely oxic in Changning area.(4)The enrichment of organic matter was mainly controlled by paleoredox condition in Long 11 sub-member,while it was controlled by the strength of paleoproductivity in Long 12 sub-member. The research results have important reference value for shale gas exploration of Longmaxi Formation in southern Sichuan.

EXPLORATION TECHNOLOGY

Removal of seismic strong shield interface based on compressed sensing technology and its application

ZHANG Yunyin, WEI Xinwei, TAN Mingyou, GAO Qiuju, ZHU Dingrong, LIN Shuxi

2019, Vol.31(4): 85–91 Abstract ( 251 ) PDF (5344 KB) ( 337 )

doi: https://doi.org/10.12108/yxyqc.20190409

The tight sandy conglomerate reservoirs in Bonan area of Jiyang Sag,Bohai Bay Basin are affected by gypsum rock,complex superimposition relationship and heterogeneity,which results in shield interface in the seismic signal. Conventional reservoir prediction methods can not meet the needs of accurate reservoir prediction,seismic identification is difficult and the reservoir is also difficult to describe. The nail-type wavelet and compressed sensing technology were used to remove the strong shield interface,highlight the seismic response characteristics of sandstone in the target layer,effectively improve the prediction ability of sandstone. This method can provide strong support for the next exploration deployment.

High precision prestack seismic velocity prediction based on well logging constraint

DU Binshan, YONG Xueshan, WANG Jiangong, NI Xianglong, QIN Tao, CHAI Xiaoying

2019, Vol.31(4): 92–100 Abstract ( 197 ) PDF (7186 KB) ( 446 )

doi: https://doi.org/10.12108/yxyqc.20190410

The prediction accuracy of velocity from seismic migration imaging processing is not high enough to meet the requirements of fine time-depth conversion and 3-D seismic velocity modeling. According to seismic wave and traveltime features,the velocity extracted from prestack seismic gathers was mutually converted, cross-validated and layered constrained with acoustic velocity of well logging to establish velocity model. On the consideration of errors between the seismic velocity and logging acoustic velocity,layered and subscale 3-D constraint correction was carried out to realize the fusion of low-frequency seismic velocity information and relatively high-frequency seismic velocity information of thin layer. The results of theoretical models and practical seismic data show that the best time window step size should be 15-20 ms for the seismic characteristic velocity and the continuous predicted velocity obtained under the quality control of logging velocity. This technology can be used in seismic imaging processing,seismic velocity modeling,variable-velocity structural mapping and so on.It has been proved that continuous velocity improved the accuracy of seismic data processing and interpretation.

Application of BP neutral network method to identification of shale lithofacies of Lucaogou Formation in Santanghu Basin

LIU Yuejie, LIU Shuqiang, MA Qiang, YAO Zongsen, SHE Jiachao

2019, Vol.31(4): 101–111 Abstract ( 297 ) PDF (6676 KB) ( 457 )

doi: https://doi.org/10.12108/yxyqc.20190411

For the identification of shale lithofacies,the traditional method of establishing lithofacies chart does not fully take into account the interference caused by the similarity of logging data and the differences in the scale of experimental data,which results in the overlap of different types of sample points in the established identification chart,the ambiguity of boundaries and the large deviation of prediction. Aiming at this problem,taking the second member of Lucaogou Formation in Malang Sag of Santanghu Basin as an example,based on the full understanding of reservoir characteristics,a BP neutral network method based on principal component analysis was adopted. Firstly,the core data of the study area were used to classified the lithofacies into three types,such as organicrich laminar facies,carbonate-rich laminar facies and rich tuff-grain laminar facies,so as to reduce the scale error with the logging data. Secondly,the lithofacies chart was established to extract logging curves such as AC,GR, DEN,CNL,Rt and so on,which were sensitive to the response of lithofacies,the factor loading geological factors of each principal component were analyzed,and three principal components PC2,PC3,PC4 containing a large amount of lithofacies information were selected. Finally,the mapping relationship between lithofacies and logging curves was established,and the lithofacies identification of well Lu1,a key well in the study area,was carried out. The results show that compared with the traditional chart identification method,the lithofacies identification method combining principal component analysis with BP neural network can effectively eliminate the interference caused by the similarity of logging curves and reduce the error caused by the difference between the core data and the logging data,as so to improve the accuracy of lithofacies identification. This method is practical for shale lithofacies identification and has certain application value.

Prediction method of channel sand body based on prestack migration in OVT domain

ZHOU Huajian

2019, Vol.31(4): 112–120 Abstract ( 365 ) PDF (8042 KB) ( 308 )

doi: https://doi.org/10.12108/yxyqc.20190412

The Sapugao reservoir in Saertu oilfield,Daqing Placanticline,is a typical clastic fluvial-delta deposit with thin interbed of sandstone and shale,and frequent sand-mud interbedding. Conventional poststack seismic reservoir prediction method can only predict some relatively thick channel sand bodies with low accuracy,and well-seismic combined with reservoir description technology is not conducive to the comprehensive application of Sapugao reservoir in Placanticline oilfield. Taking advantage of high-density seismic data from Saertu oilfield, the processing of prestack seismic data in OVT domain was carried out,and two parameters of offset and azimuth were retained in the data volume. By means of seismic sedimentology,the amplitude attributes of stratal slices in different directions reflecting the characteristics of reservoir sand bodies were analyzed. The thin interbedded channel sand bodies were predicted according to the geomorphological characteristics of the study area, and the prediction accuracy of channel sand bodies was further improved by combining well and seismic data more than 15%. This method provides an effective means to guide the description and tapping of interwell residual oil in Placanticline oilfield. with reservoir description. Compared with conventional seismic data,the prediction accuracy was improved by more than 15%. This method provides an effective means to guide the description and tapping of interwell residual oil in Placanticline oilfield.

OIL AND GAS FIELD DEVELOPMENT

Comparison of glass etching displacement experiment and finite element numerical simulation for gas-water two-phase seepage in rocks

WU Feng, YAO Cong, CONG Linlin, YUAN Long, WEN Zhu, ZHANG Fengsheng, XI Yanping

2019, Vol.31(4): 121–132 Abstract ( 369 ) PDF (12054 KB) ( 649 )

doi: https://doi.org/10.12108/yxyqc.20190413

The study of rock micro-visualization two-phase seepage characteristics is of great significance to the development of oil and gas fields. The dynamic seepage characteristics of micro gas-water two-phase fluids in rocks were studied by means of micro visual glass etching displacement experiment and finite element numerical simulation respectively,and the results of finite element numerical simulation were verified by micro-glass etching displacement experiment. The results show that the finite element numerical simulation results are basically consistent with the experimental results of glass etching displacement. There are obvious fingering phenomena in gaswater two-phase flow displacement experiment process. After displacement,water distributed in the large throats and the hole connected with the large throats was displaced by gas,while the irreducible water was mainly distributed in the small throats and macropores controlled by the small throats and blind end of the pore. When the one-phase seepage reached steady state,the flow velocity in the center of the flow channel was higher than that at the entrance. The greater the pore throat radius,the slower the pressure drop. The micro glass etching displacement experiment method can better observe micro-fingering phenomenon and gas migration jump phenomenon when passing through narrow throat,while the finite element numerical simulation method has many advantages, such as low cost,easy operation and high repeatability. The combination of micro glass etching displacement experiment method and finite element numerical simulation method is more effective in studying the seepage of gas-water two-phase fluid in rock pores.

Potential control theory based on configuration unit and remaining oil development effect

TU Yi, WANG Yahui, YAN Zhenghe, GAO Yongming, WEI Qiren

2019, Vol.31(4): 133–140 Abstract ( 315 ) PDF (5212 KB) ( 378 )

doi: https://doi.org/10.12108/yxyqc.20190414

In order to study the development effect of remaining oil,by synthetically utilizing seismic,geological and dynamic production data,combining "fine anatomy of configuration" with "potential control theory", the dynamic migration law of oil and water was studied based on single sand body configuration unit,and the migration and accumulation law of remaining oil was predicted from the migration direction and time. The model of migration and accumulation regeneration reservoir was established,and the low potential closed area was put forward as the key area for tapping remaining oil potential. Taking Y oilfield as an example,the main reservoir has few and thin interbeds,and sand bodies are distributed in succession,mainly in stacked contacts. About one year after shutdown,the scattered remaining oil migrated and accumulated to the high parts of low well control and low potential energy structures. The interbeds developed in non-main reservoirs were large and thick. Sand bodies were dominated by stacking and lateral overlapping isolated type. The vertical migration of scattered remaining oil was blocked by interbeds,and the migration direction of sand body was affected by rhythm. Lateral contact types between sand bodies determined the accumulation scale of remaining oil. After shutdown for about 3 years,the remaining oil gradually enriched and formed reservoirs in low-potential closed zones of reservoirs. The average daily oil production of well Y1-6 H in low potential closed zone of Z9 non-main reservoir is over 200 m3,water cut is less than 5%,and the production has been stable for four years. The average daily oil production of well Y1-3 H in high structural position is less than 60 m3,and water cut is about 75%. Now it has been shut down,its production effect is much lower than that of low potential closed zone. The remaining oil of other non-main reservoirs in low potential closed zone has also achieved good potential tapping effect. Potential tapping data prove the rationality of "dynamic migration and accumulation regeneration reservoir model" in low potential closed zone,which can provide technical support for remaining oil tapping in old offshore oilfields in the middle and later stages.

Improving water injection efficiency of transfer injection well in heavy oil bottom water reservoir

ZHANG Jilei, LUO Xianbo, ZHANG Yunlai, HE Yifan, ZHOU Yanbin

2019, Vol.31(4): 141–148 Abstract ( 353 ) PDF (4903 KB) ( 408 )

doi: https://doi.org/10.12108/yxyqc.20190415

In view of the problems of poor flooding effect and ineffective circulation of most injection water in heavy oil bottom water reservoir under positive rhythm,the causes of the poor flooding effect of injected water in bottom water reservoir were analyzed. A method was put forward to build a dam by placing glue at the bottom of cone-shaped changing zone of permeability,and to expand the sweep volume of water injection in a bottom water reservoir. The key parameters of the dam were evaluated by numerical simulation and streamline simulation. The results show that the poor effect of injection water flooding in heavy oil bottom water reservoir is due to the effect of positive rhythm and large amount of liquid scouring on injection water after directional well injection,which forms a U-shaped tubular ineffective water cycle in the cone-shaped changing zone of permeability, bottom water zone and production well sweep zone. The technology of "gel dam" improves the flooding effect of injected water in heavy oil bottom water reservoir. The oil increasing effect of pilot test well group is obvious, the daily oil increment is 40 m3/d. This method changes the poor effect of water flooding in bottom water reservoir,and changes the water flooding in bottom water reservoir from "enough water injection" to "effective water injection". This new water injection model is of great significance for improving the flooding effect of water injection in heavy oil bottom water reservoirs.

PETROLEUM ENGINEERING

Pressure dynamic analysis of shale gas reservoirs considering stress sensitivity and complex migration

JIANG Ruizhong, ZHANG Fulei, CUI Yongzheng, PAN Hong, ZHANG Xu, ZHANG Chunguang, SHEN Zeyang

2019, Vol.31(4): 149–156 Abstract ( 226 ) PDF (2139 KB) ( 408 )

doi: https://doi.org/10.12108/yxyqc.20190416

The permeability of shale gas reservoirs is extremely low,and the formation is stress-sensitive strongly. The hydraulic fracturing is one of the effective exploitation methods. A composite shale gas reservoir model was established by introducing some gas migration mechanisms,such as shale gas adsorption and desorption,Knudsen diffusion,unsteady cross flow and seepage. Mathieu function,Pedrosa variable substitution,regular perturbation theory,Laplace transform and Stehfest numerical inversion methods were used to solve the mathematical model,and then the typical curves of dimensionless pseudo-pressure were plotted. The sensitivity analyses were conducted on the relevant parameters,such as permeability modulus,SRV radius,outer region fracture permeability,diffusion coefficient and desorption compressibility. The results show that the gas flow can be divided into nine stages. A larger permeability modulus resulted in a larger pressure difference required for gas well constant production. The larger the SRV radius and the desorption compressibility are,the smaller the pressure difference is. The larger fracture permeability in outer zone corresponds to a smaller mobility ratio. The larger the diffusion coefficient is,the larger the apparent permeability of the shale matrix is,and the earlier the cross flow occurs. The proposed well test model can improve the accuracy of pressure dynamic analysis of shale gas reservoirs and has certain theoretical guiding significance for fracturing development of shale gas reservoirs.

Unsteady productivity model of segmented multi-cluster fractured horizontal wells in tight oil reservoir

JI Jinghao, XI Jiahui, ZENG Fenghuang, YANG Qigui

2019, Vol.31(4): 157–164 Abstract ( 292 ) PDF (2411 KB) ( 424 )

doi: https://doi.org/10.12108/yxyqc.20190417

Aiming at the difference of seepage field for fractures between segment and cluster,based on the linear flow zoning model,the unsteady productivity model of segmented multi-cluster fractured horizontal wells in tight oil reservoir was established,in which the effects of non-Darcy flow and stress sensitivity of tight oil reservoir were considered. The oilfield example verified the correctness validity of the model. The calculation of the model shows that the threshold pressure gradient mainly affects the productivity of oil wells in the middle and late stages,and the stimulated reservoir volume(SRV)formed by reservoir transformation can effectively reduce the impact of non-Darcy flow on the productivity of oil wells in the early stage. The fracture permeability stress sensitivity has great impact on oil well production. The greater the stress sensitivity coefficient,the lower the oil well production and cumulative production. When the total number of fractures is small,the segment-cluster ratio of fractures has a greater influence on the cumulative oil production. Under the same number of fractures,the larger the segment-cluster ratio,the greater the cumulative oil production. The cumulative oil production increase gradually slows down as the SRV increases. The results can provide theoretical basis for productivity evaluation of segmented multi-cluster fractured horizontal wells in tight oil reservoir.