Lithologic Reservoirs

Unconventional oil and gas are very important superseding resources in China,for poor porosity and permeability,reservoir simulation technology is necessary and large-scale hydraulic fracturing is very effective, but some consequent problems such as high water consumption,high reservoir damage and environmental pollution are inevasible. CO2 fracturing technology,which fully used the CO2 characteristics of easy to diffusion, good formation compatibility and increasing the formation energy, has advantages of saving water,protecting environment,burying CO2 and increasing oil and gas production. Laboratory experiment and field practice indicate that CO2 fracturing technology can effectively reduce reservoir damage, improve reservoir properties,reduce rock initiation pressure,form complex fracture network,replace CH4 and reduce crude oil viscosity. Compared with hydraulic fracturing technology,it can improve backflow rate above 25%,and improve the average single well production above 1.9 times. By further optimizing of technology,developing matching equipment and relevant standards,exploring the overall development of blocks,CO2 fracturing technology will greatly promote the green and efficient development of unconventional oil and gas in China.

Sedimentary evolution and its significances for petroleum exploration in the west slope of Kaikang trough,Muglad Basin, Sudan-South Sudan

HONG Liang, CHEN Bintao, LIU Xiongzhi, HUI Xuezhi, FANG Naizhen, SU Yuping

2019, Vol.31(2): 8–15 Abstract ( 280 ) PDF (7249 KB) ( 332 )

doi: https://doi.org/10.12108/yxyqc.20190202

The west slope of Kaikang trough in Muglad Basin has been proven as a hydrocarbon-enriched belt. However,no significant exploration breakthrough has been gained. In order to study hydrocarbon accumulation conditions and reservoir-controlling mechanism of multi-stage tectonic movements,fine seismic interpretation, sedimentary facies analysis and sedimentary evolution were analyzed. The results show that:(1) The study area underwent three stages of tectonic movement and formed two sets of major petroleum systems,the upper play (lacustrine mudstone seal of upper Nayil Formation and delta sandstone reservoir of lower Nayil Formation) and the lower play (lacustrine mudstone seal of Aradeiba Formation and fluvial sandstone reservoir of Bentiu Formation); (2) The stage Ⅰ rifting-depression of Early Cretaceous controlled the distribution of in-place source rock of AG Formation in the slope area,stage Ⅱ rifting-depression of Late Cretaceous controlled the development of traps in the lower play,and stage Ⅲ rifting-depression of Paleogene controlled the major period of hydrocarbon generation and expulsion that matched with the rifting. The three stages of tectonic-sedimentary evolution worked together to gain the hydrocarbon enrichment model of "fault-seal control the accumulation together,differential accumulation in multi layers" in the west slope of Kaikang trough.

Sandbody structure and its genesis of shallow-water delta of Chang 8₁ reservoir in Jiyuan area,Ordos Basin

LIU Guizhen, GAO Wei, ZHANG Dandan, CHEN Long, LI Airong

2019, Vol.31(2): 16–23 Abstract ( 364 ) PDF (4852 KB) ( 483 )

doi: https://doi.org/10.12108/yxyqc.20190203

Chang 8 oil reservoir set of Yanchang Formation in Ordos Basin belongs to shallow-water delta deposit, of which the reservoir changes rapidly and has strong heterogeneity. To identify the characteristics of reservoir heterogeneity and predict reservoir sweet spot in Jiyuan area,studies were performed on the structure characteristics,genesis and distribution of sandbodies of Chang 8 1 reservoir by using data from coring and well logging and modern sedimentary cases. The results show that there are four types of sandbody structure in this area,including composite funnel (block composite funnel and layered composite funnel),zigzag bell-shaped,isolated box and isolated finger sandbody structure. The former two types of sandbody structure are vmultiple superimposed by distributary channel and were the main oil-bearing sandbodies. The origin,type and distribution of sandbody structure are related to palaeotectonics,paleogeomorphology,base-level cycles,sediment supply and palaeoclimate. Based on the characteristics of modern shallow delta sedimentation in Poyang Lake delta,the sandbodies in the study area are multistage distributary channel deposition,which have the characteristics of superimposed reservoir vertically and sheet distribution in horizontal. This understanding will be helpful to oil and gas exploration and development of Yanchang Formation in Ordos Basin.

Characteristics and accumulation conditions of Cretaceous dolomitic mudstone gas reservoir in Hari Sag,Yin'e Basin

LIU Huchuang, WANG Wenhui, CHEN Zhijun, ZHAO Chunchen, PAN Binfeng, BAI Xiaoyin

2019, Vol.31(2): 24–34 Abstract ( 300 ) PDF (2769 KB) ( 423 )

doi: https://doi.org/10.12108/yxyqc.20190204

In recent years,great discoveries of natural gas exploration have been made in Cretaceous dolomitic mudstone in Hari Sag. For revealing the reservoir characteristics,accumulation conditions,gas reservoir distribution and its controlling factors of mudstone gas reservoirs,the studies on tectonic setting,petrologic features, physical properties,organic geochemical test and sealing conditions evaluation of source rock were carried out, and favorable exploration areas were predicted by using seismic data. The results show that (1) Hari Sag was a half graben-like basin which experienced multiple tectonic activities. On the background of continuous subsidence,mudstone reservoir formed. (2) Source rocks were composed of lime mudstone and dolomitic mudstone with abundant over-maturity organic materials. There were many types of micropore and microfracture in part of mudstone reservoir,which supplied good reservoir space for natural gas accumulation. (3) Stable tectonic setting and excellent sealing conditions prevented the loss of oil and gas effectively. Abundant natural gas was accumulated in the source and its reserve was approximately 243.2×108 m3. The deep region of half graben-like basin was the favorable area for the mudstone gas reservoir exploration. The research results have important implications for exploration of mudstone gas reservoirs in Yin'e Basin.

Characteristics and controlling factors of high-quality reservoirs of the fourth member of Dengying Formation in northern Sichuan Basin

WANG Liangjun

2019, Vol.31(2): 35–45 Abstract ( 366 ) PDF (11992 KB) ( 541 )

doi: https://doi.org/10.12108/yxyqc.20190205

To clear the characteristics and main controlling factors of Dengying Formation reservoir in northern Sichuan Basin,field outcrops and drilling core observation,rock thin-film identification,scanning electron microscopy,inclusion,cathodoluminescence,reservoir physical property testing were used to analyze the characteristics of petrology,reservoir space,diagenesis and physical properties,seismic data were used to recover the ancient geomorphology,and then the main controlling factors of the reservoir were discussed. The results show that the reservoir rocks are mainly composed of particle-bonded dolomite,algal stromatolitic dolomite and silty-fine dolomite. The reservoir space is dominated by algae-bonded lattice pores,intercrystalline dissolved pores and nearlayered dissolved pores. The reservoir generally has the characteristics of low porosity and low permeability,but high-quality reservoirs with medium pore and high permeability are developed in some areas. The platform marginal mounds and platform inner mounds facies controlled by paleo-geomorphic highlands on the edge of the rift trough are the basis for the development of high-quality reservoirs. Buried dissolution associated with thermal evolution of source rocks in the middle-deep burial stage is the key to controlling the development of a large number of dissolved pores in the fourth member of Dengying Formation. Whereas,the epigenetic karst has a weaker impact on the reservoir. High-quality reservoirs are developed in the western Yuanba to Langzhong block in the eastern margin of Mianyang-Changning rift trough,which is the superimposed favorable area for the marginal mounds facies and burial dissolution. It is a favorable gas exploration zone in northern Sichuan Basin.

Sedimentary evolution characteristics of E₃² carbonate rocks in Yingxi area,Qaidam Basin

YI Dinghong, WANG Jiangong, SHI Lanting, WANG Peng, CHEN Juan, SUN Songling, SHI Yajun, SI Dan

2019, Vol.31(2): 46–55 Abstract ( 388 ) PDF (8772 KB) ( 470 )

doi: https://doi.org/10.12108/yxyqc.20190206

In recent years,great breakthroughs have been made in oil and gas exploration of lacustrine carbonate rocks in the upper member of Xiaganchaigou Formation (E32) of the Paleogene Oligocene in Yingxi area of Qaidam Basin,showing a reserves scale of 100 million tons. In order to evaluate next hydrocarbon exploration targets in Yingxi area,based on core observation and analysis of drilling and logging data,combined with geochemical parameters such as MnO/Fe,Sr/Ba,carbon and oxygen isotopes and thin section identification,the sedimentary evolution characteristics of lacustrine carbonate rocks were studied. The results show that carbonate rocks in Yingxi area mainly developed in the lower and middle part of E32,which interbedded with gypsum-salt rocks or terrigenous clastic rocks and mainly distributed in the sedimentary center of lacustrine basin,thinning towards the margin of the basin and transforming into terrigenous clastic rocks or gypsum-salt rocks. The carbonate rocks in Yingxi area were characterized by mixed sedimentary origin,complex mineral composition and diverse lithology,and formed in closed saline water environment under arid climate,and water salinity is the main controlling factor of lithological change and development degree. This research can provide a geological basis for defining the reserves scale in Yingxi area.

Diagenesis and porosity evolution of Permian tight reservoirs in Kangning area,eastern margin of Ordos Basin

HUYAN Yuying, JIANG Fujie, PANG Xiongqi, LIU Tieshu, CHEN Xiaozhi, LI Longlong, SHAO Xinhe, ZHENG Dingye

2019, Vol.31(2): 56–65 Abstract ( 373 ) PDF (5026 KB) ( 330 )

doi: https://doi.org/10.12108/yxyqc.20190207

Giant natural gas potential exists in Kangning area in the eastern margin of Ordos Basin which is one of the tight sands gas targets in China. To investigate the diagenesis characteristics and genesis of densification, based on the data of thin sections,scanning electron microscope (SEM),X-ray diffraction,particle size analysis, the rock composition,pore type and diagenesis-porosity evolution process of Permian reservoirs were analyzed. The results show that reservoirs are dominated by fine-medium feldspathic lithic sandstone and lithic sandstone. The average content of quartz is 49%. Rock fragment and feldspar content is in average values of 36% and 15% respectively. The reservoirs are typical low porosity and extra-low permeability tight sandstone,with an average porosity of 7% and an average permeability of 0.46 mD. The pore diameter is small with fine throat and poor sorting. Additionally,secondary dissolved pore dominates the main pore system. The Permian sandstone reservoirs have experienced compaction,cementation and dissolution-replacement,which are divided into middle A-B diagenetic stage. Compaction is the key to cause the formation of tight reservoirs,resulting in a porosity loss of 16.39%. Second leading factor is carbonate cementation and clay mineral filling,which reduces porosity by 12.30%,whereas later dissolution increases porosity by 6.01%. The calculated porosity is almost equivalent to the measured average porosity of 7.46%. The above research results have a certain reference value for searching for secondary dissolution sweet spot in exploration of tight gas reservoirs in the study area.

Linear relationship between mineral content and porosity of Chang 6 reservoir in Jiyuan area,Ordos Basin

LI Xiaoyan, QIAO Huawei, ZHANG Jiankui, MA Junjie, YAN Jiangtao, LI Shutong

2019, Vol.31(2): 66–74 Abstract ( 316 ) PDF (3325 KB) ( 378 )

doi: https://doi.org/10.12108/yxyqc.20190208

Mineral content is one of the important factors affecting the physical properties of reservoir. In order to comprehensively analyze the influences of contents of different types of minerals on reservoir porosity,taking Chang 6 sandstone reservoir in Jiyuan area of Ordos Basin as an example,the regression model between mineral content (xi) and porosity (y) was established by multiple stepwise linear regression method:y=21.131-0.086 x2-0.113 x3-0.554 x4-0.370 x5-0.199 x6-0.659 x7-0.465 x8, with the quartz content (x1), feldspar content (x2),lithic content (x3),chlorite content (x4),illite content (x5),kaolinite content (x6),siliceous content (x7) and ferrocalcite content (x8) and porosity (y). The results show that the contents of chlorite,illite,siliceous and ferrocalcite have great effects on the porosity of Chang 6 reservoir, the contents of feldspar, lithic and kaolinite have little effect on the porosity,while the quartz content has almost no effect on porosity. The test of multiple regression model shows that there is a good fit between measured porosity and model porosity,and multiple stepwise regression analysis has some advantages in the study of multifactor affecting reservoir physical properties,and it can reveal the essence of influencing reservoir physical properties better than single factor analysis.

Characteristics and controlling factors of gravity flow deposits of Huangliu Formation in eastern Yinggehai Basin

LIU Wei, YANG Xibing, ZHANG Xiuping, DUAN Liang, SHAO Yuan, HAO Defeng

2019, Vol.31(2): 75–82 Abstract ( 309 ) PDF (9844 KB) ( 557 )

doi: https://doi.org/10.12108/yxyqc.20190209

Gravity flow sedimentary system has become a key exploration area in the western South China Sea. In order to systematically study the genesis and controlling factors of gravity flow sedimentary system of Huangliu Formation in eastern Yinggehai Basin,the slope break types,source supply channels and basin subsidence of the Miocene Huangliu Formation were comprehensively studied by means of drilling,logging and seismic data, displacement-distance method and 3D motion paleogeomorphology restoration. The results show that large-scale valleys developed in strike-slip transition zone on the eastern margin of the basin controlled the main source injection channel,increased slope gradient at flexural slope break promoted the formation of gravity flow,coupling of large-scale sea-level decline and abnormal subsidence in depression controlled the distribution of gravity flow deposits of LST,and diapirism changed the micro paleogeomorphology,affecting the position of gravity flow deposits. This achievement provides theoretical support for the discovery of thick sandstone gas reservoirs in well LD10-F.

Characteristics and controlling factors of organic matter enrichment of Lower Carboniferous black rock series deposited in inter-platform region,Southern Guizhou Depression

DING Jianghui, ZHANG Jinchuan, LI Xingqi, LANG Yue, ZHENG Yuyan, XU Longfei

2019, Vol.31(2): 83–95 Abstract ( 324 ) PDF (4543 KB) ( 478 )

doi: https://doi.org/10.12108/yxyqc.20190210

Organic matter is well developed in the Lower Carboniferous black rock series deposited in an interplatform region,Southern Guizhou Depression. In order to clarify the characteristics and controlling factors of organic matter enrichment in such a setting,a case study was carried out from a newly-cut roadside outcrop,by conducting total organic carbon (TOC) test,argon ion polishing-scanning electron microscopy (SEM) analysis, major and trace element tests. The results show that:(1) TOC contents of the investigated samples of Datang Formation in Southern Guizhou Depression range from 0.90% to 2.83%,with an average of 1.45%,displaying cyclic fluctuations being in accordance with the stratigraphic cycle. (2) Both the relatively low U,V and Mo concentrations and framboidal pyrite diameter mostly more than 5 μm,together with EFU-EFMo covariations and multiple redox-sensitive indicators such as U/Th, V/Cr and Ni/Co,indicate an oxic and/or dysoxic water environment in Southern Guizhou Depression during the Early Carboniferous period,which is usually considered unfavorable for organic matter accumulation and preservation. Because the water depth in the inter-platform region is relatively shallow,some organisms cannot be oxidized or degraded through rapid burial,further promoting organic matter enrichment. (3) There is no obvious correlation between TOC and U/Th, V/Cr and Ni/Co. Of the aspects that might affect organic matter enrichment,including redox conditions,paleoproductivity,and terrigenous clastic input,the paleoproductivity seems to be the dominant controlling factor. This is strongly supported by the positive correlation between Mo and TOC contents. Also,terrigenous clastic inputs have a certain dilution effect on the organic matter content. (4) The organic matter enrichment in Southern Guizhou Depression arose dominantly from increased organic carbon export with enhanced nutrient fluxes owning to the regional sea level rising during the Early Carboniferous period. The research results would provide guidance for the study of organic matter enrichment patterns and shale gas accumulation conditions in the marine-continental transitional coal-bearing strata and medium and small-sized coal-bearing basins.

Organic geochemical characteristics of shale from Dalong Formation in Jianshi area,western Hubei

QIU Xiumei, LIU Yadong, DONG Xuelin

2019, Vol.31(2): 96–104 Abstract ( 312 ) PDF (5736 KB) ( 376 )

doi: https://doi.org/10.12108/yxyqc.20190211

In order to evaluate the exploration and development potential of the black shale of Dalong Formation in Jianshi area,western Hubei,the reservoir characteristics and organic geochemical characteristics of shales in the study area were analyzed by means of FE-SEM,XRD,low temperature N2 adsorption isotherms and CH 4 adsorption isothermal experiment. The results show that the shale reservoir spaces are dominated by mineral dissolved pores and organic pores,and quartz is the major brittle mineral in shale,which has reached mediumhigh level. The shale is classified as ultra-low porosity and ultra-low permeability reservoir with a rock porosity of 0.65%-2.79% and a permeability of 0.000 8-0.462 1 mD. The TOC content ranges from 1.62% to 13.60%,indicating its high organic material content and good material basis for shale gas. The kerogen type is mainly Ⅱ,and the Ro has reached later over-mature stage. The gas content of shale samples is 0.741-3.703 m3/t,with an average of 2.714 m3/t. The adsorbing gas content appears a positive correlation with TOC content and porosity,and shows week correlation with quartz content and organic maturity. The shale of Dalong Formation in Jianshi area deserves to be exploited due to its good hydrocarbon potential and reservoir conditions.

Adsorption capacity and controlling factors of marine-continental transitional shale in Xiangzhong Depression

YANG Tao, ZENG Lianbo, NIE Haikuan, FENG Dongjun, BAO Hanyong, WANG Ruyue

2019, Vol.31(2): 105–114 Abstract ( 255 ) PDF (2582 KB) ( 420 )

doi: https://doi.org/10.12108/yxyqc.20190212

In order to study the adsorption capacity and controlling factors of black shale of Permian Longtan Formation and Dalong Formation in Xiangzhong Depression,a variety of experimental analyses such as total rock mineral content,organic geochemistry,reservoir physical properties and isothermal adsorption were carried out. The results show that:(1) Shales are mainly siliceous shales with an average quartz mass fraction of 34.4%,mostly biogenic silicon,and average clay mineral mass fraction of 24.4%. The mineral composition characteristics are similar to those of Barnett shale in the United States and high-quality marine shale of Paleozoic in Sichuan Basin. (2) Kerogen in shale is mainly type Ⅱ2,which is in mature stage. The average TOC mass fraction is 2.63%. Organic pores are developed,mainly micropores and mesopores. (3) Shale has a strong adsorption capacity,and the saturated adsorption mass volume is 0.75-8.60 m3/t,with an average of 4.51 m3/t,which has good methane adsorption capacity. (4) Shale adsorption capacity is mainly controlled by TOC content,chloroform asphalt "A",total hydrocarbon,quartz content,rock density and pore structure. Among them,TOC content is the most significant controlling factor. The marine-continental transitional shale in Xiangzhong Depression has great exploration potential.

Characteristics and main controlling factors of tight sandstone reservoir of Ahe Formation in northern Kuqa Depression

WANG Huachao, HAN Denglin, OUYANG Chuanxiang, ZHOU Jiayi, WANG Qianqian, MA Li

2019, Vol.31(2): 115–123 Abstract ( 361 ) PDF (6770 KB) ( 458 )

doi: https://doi.org/10.12108/yxyqc.20190213

In order to reveal the genesis and distribution of micropores in the Lower Jurassic tight sandstone reservoirs in Kuqa Depression,the reservoir characteristics of Ahe Formation in northern tectonic belt were studied by means of thin section analysis,scanning electron microscopy,X-ray diffraction,micro-CT scanning and laser confocal microscopy. The results show that micropores occur in plastic minerals,and their development in the plane and vertical direction is obviously restricted by the compaction effect of intervals. Tectonic stress and burial depth are the main factors affecting the plane compaction effect,and shale content is the main factor affecting the vertical compaction effect. The micropores of the tight sandstone of Ahe Formation are composed of intercrystalline micro-pores of clay minerals and weak dissolved pores in muddy matrix. Controlled by shale content,burial depth and tectonic stress,micropores are mainly developed in the second section of Ahe Formation with low shale content,and distributed in Yinan 4 well area with shallow burial depth and small tectonic stress. This is of great significance for the formation of deep tight gas reservoirs.

Multi-scale discrete fracture modeling technology for carbonate reservoir of Longwangmiao Formation in Moxi area and its application

WANG Bei, LIU Xiangjun, SIMA Liqiang, XU Wei, LI Qian, LIANG Han

2019, Vol.31(2): 124–133 Abstract ( 390 ) PDF (7766 KB) ( 579 )

doi: https://doi.org/10.12108/yxyqc.20190214

In fractured-cavern carbonate gas reservoirs with highly deviated wells and horizontal wells as the main development wells,it is difficult to obtain the fracture occurrence at different spatial locations of well points,and the precise description of fractures is inaccurate,which all influence the characterization of seepage channels in gas reservoirs and restrict the scientific and balanced development of edge water gas reservoir. Taking carbonate reservoir of Longwangmiao Formation in Moxi area as an example,based on qualitative identification of fractures in highly deviated wells and horizontal wells,the data of core photos,FMI imaging logging,prestack seismic anisotropic fracture prediction and discontinuity detection,dynamic monitoring,were used to quantitatively characterize the fracture occurrence,opening,density and porosity. Then combined with the obtained fracture parameters,a multi-scale unstructured grid discrete fracture model was establish to determine the regional distribution of high and low permeability gas reservoir,dominant water invasion channels and water invasion patterns. The results show that the large-scale and small-scale fractures are well developed in the discrete fracture model of gas reservoir in Longwangmiao Formation,and the high permeability zones are widely distributed in the form of continuous flakes. There are nine high permeability channels with edge water invasion developed in four directions around the gas reservoir,in which there are two types of water invasion:water channeling along fractures and uniformly advancing along dissolved cavities. This method and research results have reference significance for theoretical and technical research of the same super-large overpressure deep carbonate gas reservoirs, such as fine description of the fractures,characterization of the dominant channel of water invasion and establishment of water invasion model.

Prediction of glutenite reservoir based on seismic waveform indicative inversion: a case study of Upper Urho Formation in Zhongguai-Manan area

LI Yazhe, WANG Libao, GUO Huajun, SHAN Xiang, ZOU Zhiwen, DOU Yang

2019, Vol.31(2): 134–142 Abstract ( 409 ) PDF (5810 KB) ( 640 )

doi: https://doi.org/10.12108/yxyqc.20190215

The Upper Urho Formation in Zhongguai-Manan area of Junggar Basin mainly develops sandy conglomerate of fan delta front subfacies,with the characteristics of large thickness,rapid lateral variation,low maturity of rock structure and composition. The key controlling factor of glutenite reservoir in the study area is argillaceous content. According to the argillaceous content,the glutenite of Upper Urho Formation can be divided into argillaceous-bearing glutenite and argillaceous rich glutenite. It is difficult to identify the argillaceous content effectively in the normal log curve. According to the response characteristics of conventional log curve,the amplitude difference between CNL log curve and the AC log curve was used to construct the argillaceous content curve of the glutenite reservoir. The plane distribution of high-quality glutenite reservoir was predicted by seismic waveform indicative inversion,realizing the quantitative prediction of glutenite reservoir. The drilling proves that the prediction result accords with high rate and good oil and gas display,showing a good exploration prospect in this area.

Oil displacement methods for enhanced oil recovery after polymer flooding

HAN Peihui, YAN Kun, CAO Ruibo, GAO Shuling, TONG Hui

2019, Vol.31(2): 143–150 Abstract ( 301 ) PDF (1847 KB) ( 592 )

doi: https://doi.org/10.12108/yxyqc.20190216

Field tests of high concentration polymer flooding and ASP flooding after polymer flooding have been carried out in Daqing Oilfield. Although the above two methods can achieve technical effects, the amount of polymer used is large and the economic benefit is low. In order to realize low-cost and high-efficiency production,on the basis of deep understanding of reservoir characteristics after polymer flooding,according to the combination of plugging, profile control and flooding technology,three new oil displacement methods were further studied by physical simulation experiment and formula optimization technology. (1) The combined injection and oil displacement method of "plugging agent+oil displacement system",which was injected into ASP system through low initial gel particles and then injected into the system of ASP. The polymer can be greatly reduced,and the recovery factor is increased by 2.1% and the polymer consumption is 25% compared with the ASP flooding. (2) Heterogeneous composite flooding system composed by continuous phase ternary solution and discontinuous phase PPG, which can realize dynamic adjustment and displacement. After polymer flooding, heterogeneous composite flooding can improve oil recovery by 13.6%, which is 3.4% more than that of ASP flooding. (3) Composite flooding with intercalated polymer flooding after polymer flooding was developed. The residual resistance coefficient of intercalated polymer is greater than resistance coefficient,and the plugging control ability is stronger than that of common polymer. After polymer flooding,the oil recovery can be increased by 15.9%. In view of the good results obtained in laboratory experiments of the three new oil displacement methods mentioned above and the significant reduction of chemical agent dosage compared with conventional ASP flooding,it is proposed to carry out field tests to verify the technical and economic results.

A fully coupled fluid flow and geomechanics model for coalbed methane reservoir

WEI Zhijie, KANG Xiaodong, LIU Yuyang, ZENG Yang

2019, Vol.31(2): 151–158 Abstract ( 358 ) PDF (1862 KB) ( 362 )

doi: https://doi.org/10.12108/yxyqc.20190217

To more accurately characterize the complex geomechanical effects in coalbed methane reservoir,a fully coupled triple porosity dual permeability fluid flow and geomechanics model was established with consideration of poroelastic properties and multi-process transportation. The corresponding numerical solver was constructed by the fully implicit finite volumetric method,and the impacts of geomechanics on porosity and permeability and methane production were investigated. The results show that both effective stress effect and matrix shrinkage can significantly affect fracture permeability,but in opposite direction. The dominate factor is effective stress effect compared with matrix shrinkage at the early stage of primary production,but latter turns to matrix shrinkage,which makes fracture permeability firstly decreases and then rebound. The final permeability can even reach several times of its original value. As Young's modulus increases,the effective stress effect recedes,which creates bigger and earlier peak gas production. As the Langmuir strain increases,the matrix shrinkage is strengthened,which creates bigger and earlier peak gas production. The fully coupled fluid flow and geomechanics model can describe the complex fluid-structure interaction of coalbed methane reservoir more accurately,which is of great significance to the prediction of CBM productivity.

Calculation of shale fracturing pressure under physicochemical effect of formation water

ZHAO Xiaojiao, QU Zhan, SUO Xiangyu, HAN Qiang, ZHAO Huibo

2019, Vol.31(2): 159–164 Abstract ( 284 ) PDF (1688 KB) ( 343 )

doi: https://doi.org/10.12108/yxyqc.20190218

In the process of drilling,hydration occurs when the drilling fluid contacts with the surrounding rock of the wellbore, which will lead to the deformation of shaft wall and cause the occurrence of accidents such as sidewall necking, collapse and cracking. According to the theory of elastic-plastic mechanics, rock mechanics and the maximum tensile stress criterion, the shale fracture pressure model was established on the basis of Huang's model,considering the effects of additional stress field caused by the percolation of drilling fluids in rock pores of the well wall rock, rock porosity and the fluid hydration. According to field fracturing experiment data and triaxial compression test results of shale cores with different water contents,the prediction value of shale fracture pressure,and the relation curves of shale water contents with tensile strength and the fracture pressure were obtained. The results show that the error of this model is 3.65% compared with the measured value,which means that the predicted value is closer to the measured fracture pressure,and both the fracture pressure and tensile strength decrease with the increase of water contents. It shows that the water softens the shale and reduces its mechanical properties.