Lithologic Reservoirs

The stratigraphic structure of Upper Paleozoic in the marginal zone of the eastern Sichuan Basin is complex,and the stratigraphic framework and geological laws are not well understood,especially the limited understanding of the distribution of Carboniferous residual strata and sedimentary facies,which restricts the exploration and development in this zone. Based on the regional geological background,combined with the data of new drilling,new 3D seismic and wild outcrops information,a new understanding that there is a sustained paleo-uplift in Late Paleozoic named Fengjie paleo-uplift in Fengjie-Yunyang area was proposed firstly. In terms of the seismic model forward,the seismic reflection characteristics of Silurian-Devonian-Carboniferous were determined,and the Fengjie paleo-uplift was characterized. By studying the identification,distribution characteristics and tectonic evolution of Carboniferous strata under the control of paleogeomorphology,the analysis of hydrocarbon accumulation conditions of Carboniferous was completed and the favorable gas exploration zone of Carboniferous was predicted and evaluated. The studies suggest that Fengjie paleo-uplift is located about 95 km to the east of Kaijiang paleo-uplift,which is nearly parallel to Kaijiang paleo-uplift. Its overall trend is nearly north-south and slightly east,and the length of north-south axis is about 79 km,however,the width varies from east to west and the average is 14 km in 3D seismic area. Under the joint constraints of Kaijiang paleo-uplift and Fengjie paleo-uplift,the tectonic evolution of the study area can be divided into five stages：Devonian lowstand,Carboniferous lowstand, Carboniferous transgression-highstand,Carboniferous regression and Permian transgression. Because of the longterm continuous evolution of Fengjie paleo-uplift belt,the Carboniferous strata denudation zone can be formed, then with the increase of burial depth,the Carboniferous strata around the paleo-uplift was lateral docking with Silurian mudstone,and the stratigraphic traps would be formed before hydrocarbon charging,even though suffered multiple stages of structural destructions,it may still be preserved as a gas-bearing trap in the present syncline slope area,which can be considered as the foreground area for Carboniferous gas exploration. These understandings provide support for the expansion of Carboniferous gas exploration in eastern Sichuan Basin.

Pore types and genesis of tight sandstone of Silurian Xiaoheba Formation in southeastern Sichuan Basin

ZHANG Wenkai, SHI Zejin, TIAN Yaming, WANG Yong, HU Xiuquan, LI Wenjie

2021, Vol.33(4): 10–19 Abstract ( 281 ) PDF (9828 KB) ( 282 )

doi: https://doi.org/10.12108/yxyqc.20210402

In order to study the micro pore characteristics and formation mechanism of marine tight sandstone reservoirs of Silurian Xiaoheba Formation in southeastern Sichuan Basin,thin section identification,cathodoluminescence,electron probe,field emission scanning electron microscopy and high-pressure mercury injection test were carried out. The results show that：（1）The pore types of tight sandstone reservoirs of Xiaoheba Formation include residual primary intergranular pores,intergranular dissolved pores,intragranular dissolved pores, matrix pores,intercrystalline pores and microfractures. Secondary dissolved pores（intergranular dissolved pores and intragranular dissolved pores）were dominant,which were mainly formed by the dissolution of clastic feldspar and calcite cements.（2）The development of pores is affected by sedimentary microfacies,feldspar dissolution and hydrocarbon generation intensity of underlying source rocks. Within the distal bar sandstones,when the sandstones are closer to the hydrocarbon generation center and higher of feldspar contents,the secondary dissolved pores are the most developed.（3）Micro pores are developed well in Shuangliuba-Lengshuixi area and this area maintains relatively good reservoir properties. The results indicate a new direction for tight sandstone gas exploration in southeast Sichuan Basin.

Sedimentary characteristics of sandy conglomerates of Triassic Xu-3 member in northwestern Sichuan Basin

ZHANG Benjian, TIAN Yunying, ZENG Qi, YIN Hong, DING Xiong

2021, Vol.33(4): 20–28 Abstract ( 310 ) PDF (5027 KB) ( 216 )

doi: https://doi.org/10.12108/yxyqc.20210403

In recent years,there are new discoveries in natural gas exploration of the third member of Xujiahe Formation（Xu-3 member）of Triassic in northwest Sichuan Basin. In order to systematically study the sedimentary characteristics of sandy conglomerates of Triassic Xu-3 member in northwestern Sichuan Basin,drilling core observation,logging interpretation,facies identification and dominant facies analysis of sandy conglomerates were carried out. The results show that：（1）Sandy conglomerates were developed in braided channels and overflow deposition in alluvial fan and distributary channels,subaqueous distributary channels,mouth bars and distal bars in fan delta of Xu-3 member in the study area. The braided channel was mainly composed of massive conglomerate, with more conglomerates and less sandstone,and overflow deposition mainly developed tabular cross bedding and parallel bedding,with more sandstone and less conglomerates,showing positive grain order characteristics of upward thinning.（2）Fan deltas were dominated by sandstone,the braided distributary channels,subaqueous distributary channels,mouth bars and distal bars developed scour surface,tabular cross bedding,parallel bedding and sandy cross bedding. Braided distributary channels and subaqueous distributary channels have fining-upwards normal cycle as the dominate features. Mouth bars and distal bars have coarsening-upwards normal cycle as the dominate features.（3）Sandy conglomerates were mostly developed in the braided channels,overflow depo-sition and braided distributary channels,followed by subaqueous distributary channels,mouth bars and distal bars. The research results have reference significance for natural gas exploration of Triassic Xu-3 member in northwestern Sichuan Basin.

Reservoir heterogeneity and genesis of the second member of Xujiahe Formation of Triassic in Jinqiu block，Sichuan Basin

CHAI Yu, WANG Guiwen, CHAI Xin

2021, Vol.33(4): 29–40 Abstract ( 247 ) PDF (7976 KB) ( 321 )

doi: https://doi.org/10.12108/yxyqc.20210404

In order to study the heterogeneity and genesis of the second member of Xujiahe Formation of Triassic in Jinqiu blockn,Sichuan Basin,to analyze its micro displacement efficiency and remaining oil distribution,and to formulate reasonable development plan and improve development efficiency,core observation,thin section identification,scanning electron microscope analysis,mercury injection test,nuclear magnetic resonance and conventional logging analysis were carried out. The result shows that：（1）Under the effect of multi-stage tectonic movement and late diagenetic transformation, the pore types of the second member of Xujiahe Formation are diverse, the throat is generally fine, the pore throat structure and physical properties show great differences in different regions,and the heterogeneity is strong.（2）The reservoir space of the second member of Xujiahe Formation is mainly composed of secondary pores and less primary pores,which indicates that after entered the burial diagenetic environment,the sediments were mainly affected by later diagenesis,diagenetic environment and diagenetic evolution stage,forming strong heterogeneity of the present reservoir. According to the type and intensity of diagenesis and the construction or destruction of reservoir physical properties,the second member of Xujiahe Formation was divided into four types of diagenetic facies.（3）The physical properties and heterogeneity of the second member of Xujiahe Formation are affected by structure,sedimentation and diagenesis. The specific structure and sedimentary background provide prerequisite for the formation of reservoir heterogeneity. Constructive diagenesis（dissolution and fracturing）and diagenetic strength are crucial for reservoir heterogeneity. The research results can provide a reference for oil and gas exploration of the second member of Xujiahe Formation in Jinqiu block, Sichuan Basin.

Shale lithofacies and reservoir characteristics of Wufeng Formation-lower Long 1 submember of Longmaxi Formation in western Chongqing

YIN Xingping, JIANG Yuqiang, FU Yonghong, ZHANG Xuemei, LEI Zhian, CHEN Chao, ZHANG Haijie

2021, Vol.33(4): 41–51 Abstract ( 361 ) PDF (13169 KB) ( 325 )

doi: https://doi.org/10.12108/yxyqc.20210405

Shale in Wufeng Formation-lower Long 1 submember of Longmaxi Formation in western Chongqing has great potential of exploration and development. In order to clarify the difference of reservoir quality,longitudinal distribution law and influencing factors of reservoir development of different lithofacies,the lithofacies was divided combined with thin section identification,rock composition and geochemistry characteristics. Based on the data of organic carbon content,laminar structure,reservoir space and physical properties,and gas content, the reservoir characteristics,favorable lithofacies distribution and controlling factors of different lithofacies were determined. The results show that there are six kinds of shale lithofacies：organic-rich siliceous shale,moderateorganic siliceous shale,low-organic siliceous shale,low-organic calcareous siliceous shale,low-organic clay shale and extra-low-organic clay shale. The organic-rich siliceous shale is a high-quality shale reservoir with its sedimentary environment characterized by strong reducibility,deep water body,abundant organisms,high biogenic silicon content and well-developed argillaceous lamination,which is conducive to the development and preservation of contiguous organic matter and organic pores. It is mainly developed in sublayer-1 of Long 1 submember of Longmaxi Formation,providing favorable source-reservoir conditions for shale gas enrichment. The moderate-organic siliceous shale and low-organic siliceous shale are deposited in strong reducibility and shallow water sedimentary environment,with decreased organisms,low biogenic silicon content,frequent interbedding of silt lamination and argillaceous lamination,and organic pores are mainly developed in dispersed organic matter with good connectivity. So,they are potential exploitable shale gas reservoirs,and mainly developed in the top of Wufeng Formation,sublayer-2 and sublayer-3 of Long 1 submember of Longmaxi Formation. The research results deepen the understanding of the vertical distribution of favorable shale reservoirs in the study area, and provide basic data support for three-dimensional development of shale gas.

Reservoir characteristics and diagenetic traps of the first member of Permian Xiashihezi Formation in Daniudi gas field，Ordos Basin

XU Ningning, WANG Yongshi, ZHANG Shoupeng, QIU Longwei, ZHANG Xiangjin, LIN Ru

2021, Vol.33(4): 52–62 Abstract ( 362 ) PDF (6141 KB) ( 313 )

doi: https://doi.org/10.12108/yxyqc.20210406

In order to clarify the characteristics of tight clastic reservoirs and the development mechanism of diagenetic traps of the first member of Permian Xiashihezi Formation（P1x1）in Daniudi gas field,Ordos Basin,gasbearing property analysis,casting thin section identification and carbon-oxygen isotope analysis were carried out. Through the analysis of diagenetic microscopic characteristics and quantitative statistics,the petrological characteristics and diagenetic porosity evolution of P1x1 in the study area were determined,and the development mechanism of diagenetic traps was explained. The results show that：（1）The content of quartz particles in the dry interval of P1x1 is about 15% lower than that in the gas-bearing interval,and the interstitial-filling materials are mainly calcite cements and compacted dense pseudomatrix. The dry intervals are mainly distributed in the transitional zone between the two sand bodies along the main channel,the edge of the transverse channel and the relatively isolated lenticular sand bodies.（2）The diagenetic traps in the study area can be divided into calcite-cementationreplacement and compaction-silica-cementation according to their genetic differences. The former was characterized by obvious calcite cementation and reached densification before the gas accumulation stage（Middle and Late Jurassic to Cretaceous）. Particles in latter were in close contact with each other,with obvious pseudomatrix,which was characterized by "reservoir-forming and densification". The densification of reservoirs and hydrocarbon charging occured at the same time.（3）On the one hand,there is a good coupling relationship between reservoir densification and gas accumulation,and on the other hand,the large-scale calcite cementation in the A1 stage of middle diagenesis and the continuous compaction and pore reduction effect caused by high content of plastic debris. The research results can be used for reference to the exploration of diagenetic traps with similar geological conditions.

Geochemical characteristics and paleoenvironmental significance of Upper Carboniferous sedimentary strata in Malang Sag， Santanghu Basin

CHEN Yajun, JING Wenbo, SONG Xiaoyong, HE Bobin, WU Hongmei, WANG Rui, XIE Shijian, SONG Kaihui, MA Qiang

2021, Vol.33(4): 63–75 Abstract ( 324 ) PDF (7892 KB) ( 292 )

doi: https://doi.org/10.12108/yxyqc.20210407

In order to distinguish the paleoenvironment of sedimentary interbeds during the interval of Upper Carboniferous volcanic eruption in Malang Sag,Santanghu Basin,based on the trace element test results of sedimen-tary interbed samples from lava and pyroclastic rocks of Upper Carboniferous Kalagang Formation and Haerjiawu Formation,through the study of trace element geochemistry,the index charts identified by U/Th,V/Cr,V（/V+Ni）, V/Sc,Sr/Ba and B/Ga and factor screening analysis were used to distinguish the paleosedimentary environment,so as to understand the redox state of sedimentary medium. The results show that the V/Cr, V/SC, V/（V+Ni）,Sr/Ba and B/Ga ratios of sedimentary interbeds in lava and pyroclastic rocks of Kalagang Formation and Haerjiawu Formation are relatively stable, which can be used as a better combination index for distinguishing paleosedimentary environment. The sedimentary interbeds of Kalagang Formation（C2k）were formed in the transitional facies of water and land and the medium of land oxidation environment,the sedimentary interbeds of Haerjiawu Formation（C2h）were mainly formed in the medium of underwater reduction environment,with little in complex transitional environment of water and land. This geochemical method is universal and can be used to distinguish the paleosedimentary environment of sedimentary strata in volcanic eruption intermission period under different geological times and regional geological conditions.

Quantitative evaluation of natural gas diffusion loss rate: A case study of Su-X block in Sulige gas field

LI Zhiyuan, YANG Renchao, ZHANG Ji, WANG Yi, YANG Tebo, DONG Liang

2021, Vol.33(4): 76–84 Abstract ( 278 ) PDF (3837 KB) ( 235 )

doi: https://doi.org/10.12108/yxyqc.20210408

Natural gas diffusion loss rate is of great significance in quantitative evaluation of the impact of naturalgas diffusion on gas reservoir destruction. To obtain a relatively mature quantitative evaluation method,a geological model of natural gas diffusion of terrigenous clastic gas reservoir in Sulige gas field is established based on diffusion time,rock diffusion coefficient,concentration gradient,gas-bearing area and hydrocarbon expulsion intensity of source rock,and a set of quantitative evaluation method for natural gas diffusion loss rate of terrigenous clastic gas reservoir is formed. The research ideas are as follows： Firstly,the hydrocarbon generation intensity is calculated based on the data of source rock thickness and density,original organic carbon recovery coefficient,residual organic carbon content and gas hydrocarbon yield of original organic matter. Secondly,the hydrocarbon generation intensity is multiplied by the hydrocarbon expulsion coefficient to obtain the hydrocarbon expulsion intensity. Thirdly,according to Fick's first law,the formula for calculating the natural gas diffusion loss is derived,and the natural gas diffusion loss amount is calculated based on the formula,then the natural gas diffusion loss amount divide the gas-bearing area to obtain the natural gas diffusion loss intensity. Finally,the diffusion loss intensity of natural gas divide the hydrocarbon expulsion intensity of source rock to obtain the natural gas diffusion loss rate. Based on this calculation method,the gas diffusion loss rate of Su-X block in Sulige gas field is quantitatively evaluated. It is concluded that the gas diffusion loss rate in this area is mostly between 9.7% and 17.5%. The result shows that the natural gas diffusion loss rate is low and the diffusion loss of natural gas has little damage to gas reservoir. The results are in agreement with the geological reserves and development data of Sulige gas field,which indicate that the calculation method is suitable for the quantitative study of natural gas diffusion loss rate of terrigenous clastic gas reservoir.

EXPLORATION TECHNOLOGY

Self-adaptive gain-limit inverse Q filtering method based on SNR in time-frequency domain

ZHAO Yan, MAO Ningbo, CHEN Xu

2021, Vol.33(4): 85–92 Abstract ( 203 ) PDF (7640 KB) ( 252 )

doi: https://doi.org/10.12108/yxyqc.20210409

Self-adaptive gain-limit inverse Q filtering method considers the effective frequency band of seismic records,and balances the compensation of effective amplitude and the suppression of invalid noise energy. In order to suppress the noise and improve the SNR（signal-to-noise ratio）of seismic data after inverse Q filtering, based on the self-adaptive gain-limited inverse Q filtering method and signal-to-noise ratio in time-frequency domain,a self-adaptive gain-limit inverse Q filtering method based on SNR in time-frequency domain was proposed. Firstly,based on the relevant theory,the statistic of signal and noise was extracted from the adjacent seismic traces of the seismic records,and the SNR in time-frequency domain was estimated in a multi-channel average manner. Then,the cut-off frequency of the effective frequency band was determined according to the threshold of SNR. Finally,the gain-limit of amplitude compensation to the cut-off frequency of the effective frequency band was adapted,and amplitude compensation of the time-varying gain-limit for seismic records at different moments was performed. The application of theoretical model data and real seismic data shows that compared with the conventional stable inverse Q filtering method,the proposed method can effectively compensate the amplitude energy of seismic records,suppress noise outside the effective frequency band,and improve the SNR and resolution of seismic records after inverse Q filtering.

Blind source separation of seismic signals based on ICA algorithm and its application

MENG Huijie, SU Qin, ZENG Huahui, XU Xingrong, LIU Huan, ZHANG Xiaomei

2021, Vol.33(4): 93–100 Abstract ( 213 ) PDF (7694 KB) ( 277 )

doi: https://doi.org/10.12108/yxyqc.20210410

Affected by the acquisition conditions and field environment,the actual seismic data usually contains severe noise,which seriously affects the imaging quality. Therefore,it is significant to find a suitable denoising method to improve the S/N ratio of the data and thus improve the accuracy of imaging. Independent component analysis（ICA）algorithm developed with blind source separation theory is based on higher-order statistical theoretical analysis,which can achieve the purpose of separating the signal and noise by combining the independent statistics features of effective signal and noise. However,this method requires the number of the observation signals is more than source signals. Based on this,a blind sources separation algorithm of seismic signal was proposed to process the seismic data. By phase space reconstruction（PSR）,the single-channel signal was reconstructed into a multi-dimensional phase space,and the dynamic characteristics of the reconstructed phase space is consistent with the original signal. Then,in the reconstructed phase space,based on the difference of the geometric characteristics and combining the high-order statistical characteristics of the data,the noise and effective signal can be effectively separated by ICA algorithm,and achieve the purpose of improving the signal-to-noise ratio of seismic data.

Velocity modeling and imaging of volcanic rocks in Laoyemiao area， Bohai Bay Basin

SHI Wenwu, YONG Yundong, WU Kailong, TIAN Yancan, WANG Peng

2021, Vol.33(4): 101–110 Abstract ( 308 ) PDF (12312 KB) ( 276 )

doi: https://doi.org/10.12108/yxyqc.20210411

The volcanic rock reservoirs in Laoyemiao area of Bohai Bay Basin have great exploration potential. However,multi-stage volcanic rocks are widely developed in Neogene Guantao Formation and Paleogene Dongying Formation,which have strong shielding effect on seismic waves. There are a large number of strong and multiple reflections in seismic records. Moreover,the volcanic rocks and underlying strata have extremely irregular shapes and rapid changes in physical properties laterally, resulting in much seismic energy scattering, which restricts the accurate imaging of volcanic rocks and underlying strata,and seriously affects the quality of seismic data and fine oil and gas exploration in this area. The six-division signal-retained denoising technology and five-dimensional regularization technology were used together to improve the signal-to-noise ratio of seismic data and get broadband and high signal-to-noise ratio seismic gather for velocity modeling and depth migration imaging. Velocity model in depth domain was built by layer tomography combined with 3D grid tomography velocity modeling technology. The results show that the detailed imaging of volcanic rocks,middle-deep faults and cross-sectional imaging have been greatly improved,and the degree of well-seismic anastomosis has also been significantly improved compared with conventional processing methods. This technology has laid an important foundation for seismic interpretation and reservoir prediction in this area.

Shear wave velocity prediction based on one-dimensional convolutional neural network

MA Qiaoyu, ZHANG Xin, ZHANG Chunlei, ZHOU Heng, WU Zhongyuan

2021, Vol.33(4): 111–120 Abstract ( 335 ) PDF (5048 KB) ( 340 )

doi: https://doi.org/10.12108/yxyqc.20210412

Shear and compressional waves is extremely important information for identifying reservoir lithology, physical properties and fluids in geophysical exploration. Due to the limitation of acquisition technology and cost investment,shear wave data is usually lacking,and shear wave prediction has become an urgent need for petrophysical analysis. Traditionally,shear wave conversion methods based on theoretical models and empirical formulas have great limitations. Conventional machine learning models which is point-to-point cannot effectively express the spatial characteristics of logging parameters,and the inherent relationship between shear wave parameters and other logging parameters is not sufficiently represented. To this end,a study on shear wave velocity prediction methods based on one-dimensional convolutional neural network（1D-CNN）models was carried out. A deep learning regression model was established based on 16 logging parameters such as acoustic time difference,density,natural gamma and resistivity. The structural characteristics of logging parameters in the logging depth space was extracted by different scale convolution and a multi-layer network structure learned the relationship between shear wave parameters and logging parameters depth characteristics,thereby establishing a more accurate prediction model. Through the practical application in the Upper Paleozoic clastic reservoir of the Sulige gas field,it is verified that the one-dimensional convolutional neural network model has higher shear wave prediction accuracy.

Analysis and application of formation average velocity based on multiple linear regression: A case study from A oilfield in Bohai Sea

GU Zhimeng, MING Jun, LIU Chuanqi, WANG Teng

2021, Vol.33(4): 121–127 Abstract ( 243 ) PDF (2410 KB) ( 364 )

doi: https://doi.org/10.12108/yxyqc.20210413

Formation average velocity is often used for time depth conversion to reflect the real characteristics of underground structures,however,there are many factors that affect formation average velocity and it is not easy to get the accurate velocity value. The formation average velocity formula was derived under stable deposition conditions,and it was transformed into a multiple linear fitting formula of gas-sand ratio,oil-sand ratio and sandstrata ratio by analyzing the sensitive factors affecting the formation average velocity of the study layer. The known drilling information was brought into the formula and the unknown term was solved by the least square method,then the final average velocity expression was obtained. The results of numerical simulation and application in A oilfield in Bohai Sea show that the calculated value of average velocity formula based on multiple linear regression has high prediction accuracy,the relative error between the calculated value and the real value is less than 0.5%. This method can be used for reference in areas with similar geological conditions.

Identification of fluid properties of low contrast reservoir based on water-gas ratio calculation

ZHAO Jun, HAN Dong, HE Shenglin, TANG Di, ZHANG Tao

2021, Vol.33(4): 128–136 Abstract ( 244 ) PDF (3624 KB) ( 243 )

doi: https://doi.org/10.12108/yxyqc.20210414

The electrical properties of low contrast reservoir in Wenchang A sag in the Pearl River Mouth Basin have a complicated relationship with oil and gas properties. The logging response characteristics of gas and water layers are similar,so it is difficult to identify fluid properties only by conventional logging. In order to accurately identify the fluid properties of this type of gas reservoir,based on the phase permeability data,capillary pressure and other experimental data,the calculation model of the water-gas ratio was established through the phase permeability model under different water saturations and the diversion rate equation. Combined with production and test data,the identification standard of fluid with different water-gas ratio was established,and the reservoir fluid properties of Wenchang A sag were determined according to this standard. The results show that：（1）The calculated water-gas ratio is highly consistent with the actual production data,and the accuracy of the fluid interpretation results reaches 92%,which effectively improves the accuracy of fluid identification in low-contrast reservoirs.（2）The production test data plays a decisive role in the accuracy of the fluid property identification. This method is beneficial to the development of similar reservoirs.

Pore fluid division and effective pore size calculation of shale gas reservoir: A case study of Longtan Formation in Sichuan Basin

XIANG Xuebing, SIMA Liqiang, WANG Liang, LI Jun, GUO Yuhao, ZHANG Hao

2021, Vol.33(4): 137–146 Abstract ( 420 ) PDF (3277 KB) ( 305 )

doi: https://doi.org/10.12108/yxyqc.20210415

The pore structure of shale gas reservoir is complex,and the types of fluid in pores are various. According to the fluidity of fluid in pores,the pore fluids are often divided into movable water,capillary bound water and clay bound water. In order to clarify the occurrence and migration rule of pore fluid in shale gas reservoir, seven shale samples with different organic matter and mineral composition of Longtan Formation in Sichuan Basin were selected. Low field nuclear magnetic resonance（NMR）was used to measure the NMR responses of shale gas reservoir under variable centrifugal force and drying conditions at different temperatures. Based on the characteristics of the occurrence of pore fluid in the processes of centrifuging and heating,the fluid types（movable water,capillary bound water and clay bound water）in shale pores and their NMR T2 cutoff values were determined. The results show that the NMR T2 cutoff values（T2 c1）of movable water and capillary bound water change from 0.55 to 1.00 ms,with an average value of 0.717 ms,while the NMR T2 cutoff values（T2 c2）of capillary bound water and clay bound water change from 0.27 to 0.53 ms,with an average value of 0.36 ms. According to the relationship between the relaxation time of NMR T2 spectra and pore size,the cutoff values of pore size of capillary bound water and clay bound water change from 4.52 to 5.65 nm,with an average value of 4.99 nm. The research results are conducive to the classification of shale pore fluid types and the calculation of the lower limit of effective pore size,so as to provide a reliable basis for the efficient development of shale gas reservoirs.

OIL AND GAS FIELD DEVELOPMENT

Reserve producing law of combined well pattern and technology strategy of horizontal well infilling: A case study from HD oilfield in Bohai Sea

CAI Hui, QU Dan, CHEN Minfeng

2021, Vol.33(4): 147–155 Abstract ( 311 ) PDF (3957 KB) ( 259 )

doi: https://doi.org/10.12108/yxyqc.20210416

Offshore waterflooding heavy oil fields have large injection-production well spacing and low reserve producing. In order to improve the effect of oilfield development,the basic well pattern needs to be adjusted. Based on the actual HD oil field conditions and typical well pattern adjustment methods in Bohai Sea,the classic theory of seepage mechanics was used to establish a seepage model based on integrally infilled horizontal wells with inverse nine-point basic well pattern for injection-production well pattern adjustment,and the reserve producing law under different conditions was analyzed by calculating the seepage field changes of injection-production unit. The established reserve producing effect evaluation method of injection-production well pattern was used to optimize the length of the infilled horizontal wells that meets the requirements of oilfield development. The results show that the optimal length of infilled horizontal wells is 0.75 times of the original well pattern spacing by combining the actual situation of the oilfield with the reserve producing evaluation method of combined well pattern. The research result can be used as a technical reference for injection-production well pattern adjustment in Bohai Sea and similar reservoirs.

Pressure response behavior and application of commingled well in vertical combined boundary reservoir

SHI Wenyang, CHENG Shiqing, SHI Zhiliang, ZHANG Chengwei, LI Hong, TU Kun, ZHANG Yuzhe

2021, Vol.33(4): 156–165 Abstract ( 327 ) PDF (4156 KB) ( 224 )

doi: https://doi.org/10.12108/yxyqc.20210417

Given current commingled reservoir well test model is single boundary type, this paper takes the doublelayer reservoir as an example to establish a vertical combined boundary（VCB）reservoir model,and the pressure response semi-analytical solution is obtained by Laplace transformation,Bessel function,Stehfest inversion. The pressure response curves of three VCB types were drawn and the flow stages were divided. The effects of VCB types,proportion on the pressure response were analyzed. The result is shown as follows：（1）The "closed and infinite" boundary will cause pseudo-radial flow regime, and the product between the pressure derivative in pseudo-radial flow stage and closed-boundary proportion is constant.（2）The "constant-pressure and infinite" boundary causes the pseudo constant-pressure boundary flow regime,and the pressure derivative slope in pseudo constant-pressure boundary flow stage is linearly related to the constant-pressure boundary proportion. (3）The "constant-pressure and closed" boundary appears the dominant layer boundary flow regime first,followed by the constant-pressure boundary flow regime,and the product between pressure value in constant-pressure boundary flow stage and constant-pressure proportion is constant. It is concluded that the pressure response can directly diagnose the VCB type,and pressure response feature value in the boundary flow stage can quickly determine the VCB proportion. In addition,when the pressure response appears the features of the radial composite reservoir with poor permeability outer zone or dual-porosity reservoir,the well test analysis model should be carefully selected in combination with the actual reservoir geological information.

PETROLEUM ENGINEERING

Stress-sensitive productivity model of fractured horizontal wells in volcanic reservoirs

KONG Chuixian, BA Zhongchen, CUI Zhisong, HUA Meirui, LIU Yuetian, MA Jing

2021, Vol.33(4): 166–175 Abstract ( 231 ) PDF (1884 KB) ( 291 )

doi: https://doi.org/10.12108/yxyqc.20210418

Natural fractures are developed in the volcanic reservoirs which are dual medium. Due to the stress sensitivity of the reservoirs,the production of volcanic reservoirs is significantly affected by changes in formation pressure,and there is a threshold gradient pressure phenomenon,so there is currently no productivity model suitable for the characteristics of volcanic reservoirs. Based on the dual media model,a coupling multi-scale（matrixfracture zone,fracture network reform zone,partial fracture network reform zone,artificial fracture zone）seepage model of fractured horizontal wells in volcanic reservoir was established,which was solved by Laplace transformation,Duhamel principle and superposition principle in Lagrangian space. The corresponding pressure dynamic response curve and dimensionless production curve were obtained by Stehfest numerical inversion,and the sensitivity analysis of different influencing factors was performed. The results show that the width and length of the fractured zone mainly affect the intermediate flow stage,while the width,length,non-Darcy flow and stress sensitivity of the unfractured zone mainly affect the later flow stage. The established compound flow model can accurately predict the productivity of bottomless volcanic reservoirs. There is certain guiding significance for the calculation of productivity of volcanic reservoirs.

Effect of mechanical properties of pre-crosslinked gel particles on micro migration and plugging

LUO Xiangrong, ZHAO Bo, REN Xiaojuan, WEI Jing, ZHANG Zhenzhen, WANG Ganggang, ZHOU Hangxuan

2021, Vol.33(4): 176–184 Abstract ( 246 ) PDF (7133 KB) ( 231 )

doi: https://doi.org/10.12108/yxyqc.20210419

The migration and plugging characteristics of pre-crosslinked gel particles in porous media are the key factors affecting their deep profile control performance. At present,how the mechanical properties of gel particles affect their micro migration and plugging characteristics is not well understood. For the collected three kinds of pre-crosslinked gel particles,the elastic modulus analysis method based on image acquisition technology was used to study the elastic deformation ability of gel particles for the first time,and the influence of the mechanical properties of the gel particles on the micro migration and plugging was analyzed by the experiment of visual microscopic model filled with sands. The results show that No. 1 gel particle with high compressive strength and strong toughness is not easy to be broken. It has some elastic deformation ability,and its plugging capacity is strong and injection capacity is poor. No. 3 gel particle is characterized by moderate compressive strength,strong brittleness, poor elastic deformation ability,strong injection capacity and poor thus plugging capacity. No. 6 gel particle is characterized by poor compressive strength,small elastic factor,good plugging effect and injectability. This study can provide theoretical guidance and technical support for the evaluation of deep profile control performance and optimization of pre-crosslinked gel particles.