Lithologic Reservoirs

In order to explore the dominant factors of hundred-million-ton lithologic reservoirs in Bohai Sea,based on three-dimensional seismic and drilling data,the sequence stratigraphic framework and the development characteristics of lithologic traps in extremely shallow water delta were analyzed. Combined with research and experimental simulation of late fault system,the reservoir-forming regularity,reservoir-forming model and main controlling factors of lithologic reservoirs were analyzed,and the key factors of reservoir-forming of hundred-millionton lithologic reservoirs were analyzed. A three-component reservoir control model of "ridge-fault-sand" was established. That is,the "convergent ridge" controls the dominant position of primary migration and accumulation of oil and gas,and determines the scale of oil and gas migration to shallow layer. "Ridge-fault" coupling controls the further migration of oil and gas to shallow layers,and "fault-sand" coupling controls the development of largescale lithologic traps and the degree of oil and gas filling. Under the guidance of this model,100 million tons of lithologic reservoirs of Neogene Minghuazhen Formation of QHD 33-1S have been discovered in the edge of QHD 33-1 small oil field in Shijiutuo old area. It is the first commercial discovery of lithologic reservoirs in Bohai Sea under the restriction of high economic threshold.

Genesis types and accumulation characteristics of crude oil in southeast slope of Weixinan Depression,Beibuwan Basin

JIN Qiuyue

2020, Vol.32(1): 11–18 Abstract ( 296 ) PDF (2395 KB) ( 537 )

doi: https://doi.org/10.12108/yxyqc.20200102

The southeast slope in Weixinan Depression of Beibuwan Basin is an important hydrocarbon accumulation area. In order to study the genesis types and accumulation characteristics of its crude oil,the biomarkers and isotopic geochemical characteristics of the crude oil in the southeast slope were analyzed. The results show that:(1)The crude oil in the southeast slope can be divided into two types. The first type of crude oil has low 4-methyl sterane abundance and low carbon isotope, and mainly distributed in the first member of Liushagang Formation,while the second type of crude oil has high 4-methyl sterane abundance and higher carbon isotope,and mainly distributed in the second and third member of Liushagang Formation and Weizhou Formation.(2)Hydrocarbon source rocks in the southeast slope can be divided into two hydrocarbon combination through geochemistry characteristics in combination with sedimentary environment. The upper hydrocarbon combination mainly includes the mudstone of the first member of Liushagang Formation and the middle mudstone of the second member of Liushagang Formation,while the lower hydrocarbon combination mainly includes the bottom oil shale of the second member of Liushagang Formation and the upper mudstone of the third member of Liushagang Formation.(3)Through analyzing the biomarkers and isotopic characteristics of oil and source rocks, it is concluded that the first type of crude oil is from the upper hydrocarbon combination,and the second type of crude oil is from the lower hydrocarbon combination. The petrofacies of source rocks controlled the distribution of different types of crude oil. The second and third member of Liushagang Formation,Jiaowei Formation,Xiayang Formation and basement weathering crust in the southeast slope are all favorable areas for searching for the second type of crude oil,while lithologic traps in the first member of Liushagang Formation are favorable areas for searching for the first type of crude oil.

Development characteristics and genetic mechanism of mid-deep reservoirs in Ledong area,Yinggehai Basin

LI Wei, LIU Ping, AI Nengping, SHAO Yuan, HOU Jingxian

2020, Vol.32(1): 19–26 Abstract ( 334 ) PDF (5081 KB) ( 531 )

doi: https://doi.org/10.12108/yxyqc.20200103

In order to research the development characteristics and genetic mechanism of mid-deep reservoirs in Ledong area of Yinggehai Basin,analysis of casting thin section,scanning electron microscope observation, physical properties test and mercury injection experiment were carried out. Combined with logging,well testing data,regional burial history,hydrocarbon charging time and overpressure genesis,a detailed study was carried out on the origin of low permeability and development mechanism of "sweet spots". The results show that:(1)The mid-deep reservoir sandstone in Ledong area is mainly feldspar debris sandstone with low maturity. The secondary dissolved pore is developed,and the pore texture of sandstone is dominated by large-medium pore and fine throat. The reservoir properties are mainly of low porosity and low permeability,ultra-low porosity and ultra-low permeability.(2)The mid-deep reservoirs have experienced strong compaction,and the high content of plastic minerals leads to weak compaction resistance. Not only that,the content of cement is high,and the overpressure formed in late stage has limited protective effect on the reservoirs,which results in the low permeability of the reservoirs.(3)The development of sweet spot reservoir is mainly due to a large number of secondary dissolved pores produced by dissolution,and the dissolution fluid is mainly organic acid carried by hydrocarbon charging. The structural action and temperature-pressure environment play a constructive role in improving reservoir physical properties. The research results can be used for reference in searching for secondary pore development zones in the mid-deep formation of Yinggehai Basin.

Accumulation conditions and exploration potential of shale gas of Ziliujing Formation in Shizhu area,Sichuan Basin

WANG Deng, YU Jianghao, ZHAO Xuesong, CHEN Wei, HUANG Jiaqi, XU Cong

2020, Vol.32(1): 27–35 Abstract ( 347 ) PDF (5045 KB) ( 451 )

doi: https://doi.org/10.12108/yxyqc.20200104

In order to study the shale gas accumulation conditions of Ziliujing Formation in Shizhu area of Sichuan Basin,field geological outcrop survey,core observation,organic geochemical analysis,X-ray diffraction test, physical property analysis and scanning electron microscopy observation were carried out. The results show that:(1)The Dongyuemiao member of Ziliujing Formation in Shizhu area was formed in semi-deep lake facies,and the lithology was dominated by shale with a thickness of 30-95 m.(2)The mudstone of the target zone was characterized by high abundance of organic matter and moderate thermal evolution. The TOC mass fraction is 0.49%-2.02%,the Ro average is 1.27%,and the brittle mineral average is 58.8%.(3)The content of adsorbed gas in rocks is high,the average mass volume is 2.78 m3/t,and the burial depth is moderate,so it has good exploration prospects.(4)The Qiaotouba-Jiannan-Shangshuiba area in Shizhu area was predicted to be a favorable area for shale gas exploration by superimposition method,and the geological resource of shale gas was estimated to be about 390.5 billion m3. The research results can provide reference for shale gas exploration of Ziliujing Formation in Shizhu area,Sichuan Basin.

Development pattern and genesis of gentle slope shallow water delta front sand bodies of Chang 8₂ sand set in Zhidan area,Ordos Basin

ZHANG Jiaqiang, LI Shixiang, ZHOU Xinping, LIANG Yicai, GUO Ruiliang, YAN Cancan, CHEN Junlin, LI Shutong

2020, Vol.32(1): 36–50 Abstract ( 280 ) PDF (9642 KB) ( 415 )

doi: https://doi.org/10.12108/yxyqc.20200105

The oil and gas accumulation conditions in the front area of the shallow water delta are superior,and the internal sand bodies are always the crucial target of conventional oil and gas exploration. The key to the successful exploration is to find out their sedimentary law and model. Based on the core,thin section and logging data of Chang 82 sandstone set in Zhidan area of Ordos Basin,the petrological characteristics,mineralogical characteristics,logging response characteristics,spatial distribution and genetic types of Chang 82 sand bodies in this area were studied. On the basis of considering the palaeogeomorphology,palaeowater depth and palaeoclimate of the lake basin during the sedimentary period,the sedimentary model of the sand bodies was established,and the genesis was analyzed. The results show that there are two types of shallow water delta front sand bodies with distinct sedimentary characteristics in Zhidan area,which are underwater distributary channel sand bodies and mouth bar-beach bar composite sand bodies. The rock types of the two types of sand bodies are mainly finegrained feldspathic sandstone and lithic feldspathic sandstone. The single-layer thickness of the underwater distributary channel sand body is larger, the sand maturity is lower, the vertical multi-stage sand bodies are continuously stacked,and the planar connectivity is poor,while the mouth bar-beach bar composite sand bodies are characterized by smaller single layer thickness,higher sand maturity,frequent mud-silt thin layer and good planar connectivity. Zhidan area is located on the shallow gentle slope of the lake basin,and the type of sand body development is closely related to the lake level. The sedimentation of underwater distributary channel sand bodies is mainly controlled by the fluvial progradation during the low lake level period,while the mouth bar-beach bar composite sand bodies are mainly related to the Lake wave transformation during the high lake level period. The research results can be used for reference in the study of the sand body system in gentle slope shallow water delta front of lake facies.

Characteristics and controlling factors of Chang 6 and Chang 7 reservoirs in southwestern Ordos Basin

CHEN Yiting, LIU Luofu, WANG Mengyao, DOU Wenchao, XU Zhengjian

2020, Vol.32(1): 51–65 Abstract ( 356 ) PDF (13892 KB) ( 382 )

doi: https://doi.org/10.12108/yxyqc.20200106

In order to study the characteristics and controlling factors of Chang 6 and Chang 7 reservoirs in southwestern Ordos Basin,core observation and description,casting thin section identification,scanning electron microscopy analysis and other analysis and testing were carried out. The results show that:(1)Four types of sedimentary facies can be identified in the study area,including vertical sedimentation,lateral sedimentation,presedimentation and turbidity,and various sedimentary microfacies,such as underwater distributary channel,mouth bar,gravity flow sand body,can be distinguished,and six diagenetic facies can be identified.(2)The physical properties of reservoirs are controlled by both sedimentation and diagenesis. Chlorite films are developed in rocks with coarse original sedimentary components and low content of plastic minerals,and secondary dissolved pores are more developed,reservoir physical properties are better. Rocks with fine original sedimentary components and high content of plastic minerals have strong compaction,with siliceous and carbonate developed,which are easy to form compact reservoirs.(3)Sedimentary facies zones determine the congenital material basis of rocks, and diagenesis controls the effect of later transformation of rock physical properties. Both of them control the reservoir properties of present-day rocks. The results of this study can be used to guide the prediction of favorable reservoirs in southwestern Ordos Basin.

Characteristics and evaluation of Chang 7 source rock of Yanchang Formation in Fuxian area, Ordos Basin

HUANG Yanjie, BAI Yubin, SUN Binghua, HUANG Li, HUANG Changwu

2020, Vol.32(1): 66–75 Abstract ( 426 ) PDF (2360 KB) ( 502 )

doi: https://doi.org/10.12108/yxyqc.20200107

In order to study the characteristics and hydrocarbon generation potential of Chang 7 source rock of Yanchang Formation in Fuxian area of Ordos Basin,core analysis,well logging research, kerogen microscopy, vitrinite reflectance(Ro) test,rock pyrolysis analysis, gas phase chromatography and chromatography-mass spectrometry were carried out. The results show that:(1) The average thickness of Chang 7 source rock in Fuxian area was 45 m,the TOC mass fraction averaged 5.94%,and the average hydrocarbon generation potential(S1+S2) was 13.1 mg/g.(2)The types of organic matter were mainly type I and Ⅱ1,and the source of the source rock was mainly composed of lower aquatic organisms and contained some higher plants. The water body was a reducing environment during sedimentation.(3)The vitrinite reflectance averaged 0.76%. Among the biomarker compounds, C31 hopane 22S(/22R+22S),20RC29αββ(/αββ+ααα)and αααC2920S(/20S+20R), the average values were 0.52,0.62,0.49,respectively,reflecting the evolution of organic matter into the peak stage of oil production.(4)On the plane, Chang 7 source rocks in the central and northwestern Fuxian area have large thicknesses and stronger hydrocarbon generation capacity, which is a favorable zone for further exploration. The research results play an important guiding role for fine exploration in Fuxian area of the Ordos Basin.

Genesis of authigenic chlorite in tight oil reservoirs and its influence on physical properties: a case study of Shaximiao Formation in NE of central Sichuan Basin

WU Jiayang, LYU Zhengxiang, QING Yuanhua, YANG Jiajing, JIN Tao

2020, Vol.32(1): 76–85 Abstract ( 396 ) PDF (7126 KB) ( 338 )

doi: https://doi.org/10.12108/yxyqc.20200108

In order to study the occurrence,genesis and influence of authigenic chlorite in the tight oil reservoirs of Middle Jurassic Shaximiao Formation in NE of central Sichuan Basin,the experimental data such as polarized microscopic slice,mineral X-ray diffraction,electron probe and scanning electron microscopy were used to systematically analyze the authigenic chlorite. The results show that the authigenic chlorites in the study area are iron-magnesium transitional chlorites rich in iron. The granular-coated chlorite was formed in the syngenetic-early diagenetic A stage,the pore liner was the main occurrence of chlorite,which was formed in the early diagenetic A stage,and the pore-filled chlorite was mainly formed in the middle diagenetic A2 stage. The Fe and Mg required for the formation of authigenic chlorite were derived from hydration hydrolysis and dissolution of magmatic rock cuttings and biotite,and Fe and Mg ions adsorbed by the clay mineral conversion release layer in mudstone adjacent to the stratum. There are three kinds of formation mechanism of chlorite:(1)in the syngenetic-early diagenetic A stage,symbiotic hydration hydrolysis of silicate minerals and montmorillonite conversion to chlorite in Fe and Mg fluids; (2)in the early diagenetic A stage,the conversion of montmorillonite to illite in adjacent mudstones provided sufficient Fe and Mg ions; (3)in the middle diagenetic A2 stage,it was related to the dissolution of silicate minerals by carbonic acid formed by decarboxylation of organic acids and the conversion of kaolinite(or illite)to chlorite. The chlorite liner can improve the compressive strength of sandstone and facilitate the preservation of pores and throat. The chlorite liner with suitable thickness(> 7 μm)can effectively inhibit the secondary expansion and filling of the quartz. The reservoir with chlorite liner developed is conducive to the preservation of primary pores,enabling pore water to react further with the surrounding rock particles to ensure the dissolution of the later stage. Therefore,chlorite liners play an important role in the formation of tight oil reservoirs in the study area.

TOC prediction technology based on optimal estimation and Bayesian statistics

ZHAO Wanjin, GAO Haiyan, YAN Guoliang, GUO Tongcui

2020, Vol.32(1): 86–93 Abstract ( 288 ) PDF (3972 KB) ( 454 )

doi: https://doi.org/10.12108/yxyqc.20200109

The total organic carbon(TOC)content in tight rock formations often directly indicates the location of oil and gas reservoirs,but dense rock formations often have complex lithology configurations,so it is difficult to identify effective source rocks by using conventional geophysical techniques. This paper proposed a TOC wellseismic joint prediction technology based on optimal estimation and Bayesian statistical classification. The TOC estimated by the conventional method was taken as the initial value,and the initial value of TOC was corrected by using the constructed rock density calculation model and optimization theory. The TOC log curve with the best matching with the laboratory sample was obtained. Based on the analysis of TOC sensitive parameters,the inversion TOC sensitive parameters were converted into TOC probability volume spatial distribution by Bayesian statistical classification method. This technology was applied to the prediction of lacustrine dense marl reservoirs,providing a reliable basis for the deployment of high-yield oil wells ST3. The practical application results verified the effectiveness of the technology,and the technology can be applied to the prediction of effective source rocks with similar geological features.

Monitoring and evaluation technology for high resolution processing of seismic data

DIAO Rui

2020, Vol.32(1): 94–101 Abstract ( 240 ) PDF (6458 KB) ( 474 )

doi: https://doi.org/10.12108/yxyqc.20200110

Thin-bedded lithologic reservoirs have gradually become an important field of exploration and development. Thin-bedded sand bodies require higher requirements for improving resolution processing methods and results fidelity. In the processing of high resolution,the research mainly focuses on high resolution algorithm, and lacks systematic and comprehensive monitoring and evaluation methods. In order to meet the urgent need of improving resolution,the research of monitoring and evaluation technology for improving seismic resolution was carried out. The processing flow of improving high resolution was monitored comprehensively and reliably from nine aspects of attribute characteristics,and the quantitative evaluation and analysis of processing results was realized. Thus,the processing technology,process and parameters of improving resolution were optimized efficiently,so as to obtain the best high-resolution data. This technology has been applied in Zhuang-3 well area in the central of Junggar Basin. The whole processing of improving high resolution was evaluated and analyzed. The problems of conventional processing parameter test were solved,and the recognition ability of thin sand body was significantly enhanced after improving seismic resolution.

Organic facies and well logging evaluation of source rocks in centeral-south sag of Miaoxi Depression and its surrounding areas,Bohai Sea

SUN Zhe, PENG Jingsong, JIANG Shangkun, YE Tao, GUO Ying

2020, Vol.32(1): 102–110 Abstract ( 238 ) PDF (4261 KB) ( 428 )

doi: https://doi.org/10.12108/yxyqc.20200111

Aiming at the problems of low exploration degree and strong heterogeneity of source rocks in the centeral-south sag of Miaoxi Depression and its surrounding area,Bohai Sea,based on the division of organic facies and the improved logging evaluation method of source rocks,combined with 3-D seismic data and the characteristics of sedimentary system in the study area,the organic facies types and the development characteristics of high-quality source rocks of the Es3 and Es4 were described. The results show that the source rocks of Es3 in the study area are mainly C and D/E facies, and the quality of the source rocks is good as a whole, but there is a certain degree of heterogeneity. The C-facies source rocks are mainly distributed in the south subsag of centeral-south sag of Miaoxi Depression and the junction of eastern subsag of Huanghekou sag and centeral-south sag of Miaoxi depression,while the distribution in the north subsag is relatively limited. The organic facies of the source rocks of the Es4 is mainly F facies,and the development of high-quality source rocks is limited. The C facies source rocks are mainly distributed in the south subsag of centeral-south sag of Miaoxi Depression. The south subsag is a superimposed development area of high-quality source rocks of Es3 and Es4,and it is a favorable zone for further exploration.

Three-parameter AVO inversion method of pore modulus based on PP and PS wave simultaneous joint inversion

DING Yan, DU Qizhen, LIU Lihui, FU Liyun, LENG Xuemei, LIU Zixuan

2020, Vol.32(1): 111–119 Abstract ( 286 ) PDF (4730 KB) ( 419 )

doi: https://doi.org/10.12108/yxyqc.20200112

Equivalent fluid bulk modulus is a sensitive fluid indicator,which is of great significance in hydrocarbon identification of complex reservoirs. However,conventional single P wave AVO inversion method for fluid identification using Gassmann fluid factor has problems including poor precision,multi-solution,and ambiguous description of geological boundaries,which restricts the applications of these techniques in fluid identification. Based on rock physical model of two-phase medium,a new linear approximation of PP wave and PS wave Zoeppritz equation which consists of equivalent fluid bulk modulus,shear modulus of rock skeleton and porosityrelated gain was derived firstly. Then,simultaneous joint inversion was carried out under the constraint of Bayesian theory and Cauchy prior distribution with the combination of PP wave and PS wave data. The test results of Marmousi2 reservoir model show that compared with the inversion methods merely using PP wave data,simultaneous joint inversion based on independent PP wave and PS wave can provide more stable inversion results, higher accuracy and clearer description of geological boundary characteristics. The application in A oilfield proved the feasibility and robustness of this method. The proposed PP and PS wave simultaneous joint inversion method has certain reference for improving reservoir fluid identification.

Analysis and countermeasures of seismic prediction traps for Xu-2 gas reservoir in central Sichuan Basin: a case study from Longnyusi block

LI Xinyu, ZHANG Jing, BAO Shihai, ZHANG Lianqun, ZHU Qiliang, YAN Haijun, CHEN Sheng

2020, Vol.32(1): 120–127 Abstract ( 313 ) PDF (8556 KB) ( 287 )

doi: https://doi.org/10.12108/yxyqc.20200113

The second member of Xujiahe Formation of Upper Triassic in central Sichuan Basin is rich in natural gas resources and has great potential for exploration and development. However,in recent years,there are neither significant exploration discoveries nor good economic benefits. The reason is the unclear understanding of the distribution of the enriched area of Xu-2 reservoir. Based on study,three kinds of fatal prediction traps in the seismic prediction of the Xujiahe gas reservoir enrichment area were summarized:(1) Insufficient understanding of the vertical distribution of the effective reservoir and its corresponding seismic reflection characteristics; (2) the mudstone interlayer in upper Xu-2 were well developed,the reflection characteristics of mudstone interlayer and effective reservoir are similar;(3) the difference of seismic reflection characteristics between gas layer,water layer and dry layer is small. According to the three kinds of prediction traps in the prediction process,some targeted technical countermeasures were formed,such as forward modeling to identify reservoir characteristics,frequency division inversion to identify mudstone,prestack AVO technology to distinguish gas layer,water layer and dry layer,which were applied in the prediction of Xu-2 gas reservoir in Longnyusi block,central of Sichuan Basin,and the new drilling forecast compliance rate was more than 90%. These techniques improve the prediction accuracy of Xu-2 gas reservoir and effectively support the exploration and development of the Xu-2 gas reservoir.

Early identification methods of water invasion in weak water drive gas reservoirs in Sebei gas field,Qaidam Basin

DENG Chenggang, LI Jiangtao, CHAI Xiaoying, CHEN Fenjun, YANG Xiyan, WANG Haicheng, LIAN Yunxiao, TU Jiasha

2020, Vol.32(1): 128–134 Abstract ( 293 ) PDF (2256 KB) ( 435 )

doi: https://doi.org/10.12108/yxyqc.20200114

In the early stage of development of weak water drive gas reservoirs,the water invasion characteristics are not obvious,so it is difficult to identify them. Water monitoring and water-gas ratio curve analysis were often used to identify water invasion characteristics of gas reservoirs,but these methods can only be used after formation water enters gas wells,which is not conducive to taking preventive measures in advance. Taking A gas reservoir with weak edge water energy in Sebei No. 2 gas field as an example,the early water invasion characteristics of gas reservoir were identified by introducing production indicator curve method,water storage volume coefficient method and apparent geological reserves method,and the curve characteristics under different recovery degrees were compared. The results show that the apparent geological reserve method is sensitive to water invasion of gas reservoirs,and the corresponding recovery degree is the lowest when the curve warping point occurs, which is 20% lower than the field experience method. The result of water invasion identified by the apparent geological reserve method is more reliable,and the water invasion characteristics of gas reservoirs can be found earlier. The research results have guiding significance for early identification of water invasion characteristics of weak water drive gas reservoirs without fracture development and relatively homogeneous porosity.

Microscopic water flooding efficiency and main controlling factors of tight sandstone reservoir

SONG Mingming, HAN Shuqiao, DONG Yunpeng, CHEN Jiang, WAN Tao

2020, Vol.32(1): 135–143 Abstract ( 363 ) PDF (4226 KB) ( 393 )

doi: https://doi.org/10.12108/yxyqc.20200115

Aiming at the problems of low single well production,fast water cut rise and complex residual oil distribution during the water flooding of Chang 7 reservoir in Wuqi Oilfield,Ordos Basin,microscopic water flooding seepage experiment was carried out on real core samples of Chang 7 reservoir in the study area by using selfdesigned high-temperature and high-pressure micro-model holder. Combined with cast thin slice analysis,scanning electron microscopy,X-ray diffraction,high pressure mercury penetration and NMR testing,the microscopic water flooding seepage characteristics under different pore structure types were studied. The effects of reservoir physical properties,microscopic pore structure,movable fluid parameters,clay minerals,displacement pressure and water injection volume on water flooding efficiency were discussed. The results show that the characteristics of microscopic water flooding of Chang 7 reservoir are mainly reticular displacement and dendritic displacement,followed by uniform displacement and rare serpentine displacement. There are great differences in displacement efficiency and residual oil distribution among different types of displacement characteristics. The displacement efficiency of uniform displacement is the highest(48.84%),and that of serpentine displacement is the lowest(31.73%). 75% of the remaining oil occurs in the pore throat as clusters and oil films. There are many factors affecting water flooding efficiency,among which movable fluid parameters are more accurate than other physical parameters to reflect the relationship with oil displacement efficiency. The research results provide a theoretical basis for the adjustment of the development schemes of different reservoir types.

Prediction method of well pattern infilling effect for ultra-low permeability reservoir in X oilfield

ZHANG Yichao, CHEN Minfeng, QU Dan, MAO Meifen, YANG Ziyou

2020, Vol.32(1): 144–151 Abstract ( 247 ) PDF (1774 KB) ( 366 )

doi: https://doi.org/10.12108/yxyqc.20200116

The dynamic development effect prediction research based on actual reservoir well pattern infilling adjustment can provide adjustment basis for oilfield development planning. Based on the dynamic analysis of the development before and after well pattern infilling adjustment for ultra-low permeability reservoir in X-oilfield, the change law of infilling yield-increasing effect and its main influencing factors were determined. Based on the typical numerical model established to reflect the characteristics of actual reservoir,the response surface design method and stepwise regression method were applied to comprehensively study the impact of different factors on the yield-increasing effect after well patter infilling,and the prediction model of yield-increasing effect of well pattern infilling adjustment considering multi-factors and reflecting the characteristics of ultra-low permeability reservoirs was obtained. The practical application of the prediction model for the ultra-low permeability reservoir in X oilfield shows that the prediction accuracy is high,and it has strong pertinence and practicability. The method established to characterize the yield-increasing effect of infilling adjustment can provide reference for the prediction of infilling adjustment effect of ultra-low permeability reservoirs,and provide a reliable basis for the development planning of such reservoirs.

Pressure transient analysis for separate-layer acid fracturing well of tidal flat fractured carbonate reservoirs in western Sichuan Basin

SHI Wenyang, YAO Yuedong, CHENG Shiqing, GU Shaohua, SHI Zhiliang

2020, Vol.32(1): 152–160 Abstract ( 280 ) PDF (2817 KB) ( 376 )

doi: https://doi.org/10.12108/yxyqc.20200117

In order to reflect the complex flow characteristics of reservoir after separate-layer acid fracturing, aiming at tidal flat fractured carbonate reservoir,a pressure transient analysis model considering crossflow for separate-layer acid fracturing wells in fractured carbonate reservoir was established,and the bottom-hole pressure was obtained by Laplace transformation and numerical inversion. According to the type curves of pressure and its derivative,the flow stages were identified and divided,and the effects of interlayer physical property differences, crossflow and separate-layer modification differences on pressure response were analyzed. The results show that there are seven flow stages of tidal flat fractured carbonate reservoir in separate-layer acid fracturing,and the type curve has the flow characteristics of composite model and layered crossflow model. The greater the difference of interlayer properties,the more obvious the crossflow and concave on the pressure derivative curve are. The separate-layer acid fracturing degree and scope both affect the time and scale of transition flow occurrence. The higher the mobility ratio of high-permeability layer is,the more obvious the transition flow stage is,and the pressure derivative value is the half of the mobility ratio of high-permeability layer during outer radial flow stage. The model can provide a method for quickly identifying the acid fracturing degree of high-permeability layer, which can be used to evaluate the acid fracturing effect of multi-layer fractured carbonate reservoir and determine the degree of acid fracturing modification of individual layer.

CO₂ huff and puff simulation in horizontal well with random fractal volume fracturing

ZHOU Rui, SU Yuliang, MA Bing, ZHANG Qi, WANG Wendong

2020, Vol.32(1): 161–168 Abstract ( 243 ) PDF (2347 KB) ( 510 )

doi: https://doi.org/10.12108/yxyqc.20200118

At present,the horizontal drilling with large-scale hydraulic fracturing is the main technology to mine shale gas while volumetric fracturing would induce cracks underground and communicate natural cracks to form complex fracture networks eventually. In order to simulate the seepage flow of shale gas in the complex fracture network and characterize the network on the shale gas model,a random fractal network model was established through a two-porosity component simulator combined with the random fractal geometry system. Based on the above model,five schemes for carbon dioxide stimulation to extract shale gas were further studied. The results show that CO2 huff and puff can significantly increase the production of shale gas,and the increase of injection pressure and injection time can improve the ultimate recovery. The latter has the optimal value in the process of shale gas production,and too early or too late injection timing will make the production worse,and there is an optimal injection timing range in each CO2 injection cycle. The fractal fracture network model provides a theoretical basis for further research on the simulation of fracture CO2 huff and puff production of shale gas reservoir.