Lithologic Reservoirs

In order to study the adsorption characteristics of typical coal reservoirs of different coal ranks in Inner Mongolia,coal samples from three representative areas including the northern areas in Ordos Basin,Baiyinhua coalfield in Erlian Basin group and Yakeshi-Wujiu coalfield in Hailar Basin group were conducted isothermal adsorption tests at different temperatures and pressures. The results show that:(1) Under the reservoir temperature, the adsorption capacity of long flame coal in Yakeshi-Wujiu coalfield is the strongest,followed by high-rank coal in northern Ordos Basin,and the adsorption capacity of lignite in Baiyinhua coalfield is the smallest.(2) The adsorbability of the three coal samples decreased with the increase of temperature,and it decreased rapidly within a certain temperature range called sensitive temperature. The sensitive temperature of coal reservoirs in northern Ordos Basin is the highest,followed by Yankeshi-Wujiu coalfield and Baiyinhua coalfield.(3) The variation of the number of hydroxyl and carboxyl functional groups and the stress compaction are the main factors affecting the adsorption capacity of coal reservoirs.(4) The difference of adsorptive sensitivity temperature of coal reservoir is closely related to coal metamorphism and pore structure. In northern Ordos Basin,the coal metamorphism reaches lean coal stage,and the coal reservoir is with poor connectivity and dominantly developed nano-sized pores,with high adsorption sensitivity temperature. In Yakeshi-Wujiu coalfield,the coal metamorphism reaches long flame coal stage,and the coal reservoir is with good connectivity and dominantly developed nano-sized pores,with medium adsorption sensitivity temperature. In Baiyinhua coalfield,the coal is not metamorphosed and is in lignite stage,and the coal reservoir is with good connectivity and well-developed nano-micron pores, with low adsorption sensitive temperature. The research results provide other possibilities for coal reservoir transformation, makes it no longer limited to fracturing technology.

Sedimentary characteristics and reservoir accumulation model of salt lake of Paleogene Qianjiang Formation in Jianghan Basin

HUANG Hua, YUAN Juanmei, PENG Wei, ZHANG Liang, WEN Hui

2021, Vol.33(2): 9–16 Abstract ( 477 ) PDF (3664 KB) ( 381 )

doi: https://doi.org/10.12108/yxyqc.20210202

Jianghan Basin is a typical continental salt lake basin. The main oil and gas producing layer is the salt interlayer of Paleogene Qianjiang Formation. In order to study the sedimentary characteristics and reservoir forming model of salt lake,the paleogeomorphology,paleostructure and paleoclimate of Qianjiang Formation Late Eocene were reconstructed,and SEM analysis and sand body distribution characteristics were carried out. The results show that:(1) The formation of the salt lake basin is based on the "high mountain and deep basin" paleogeomorphology and deep concave paleostructure controlled by faults. The climate is mainly subtropical drought,supplemented by alternation of dry and wet,forming multi rhythm deposits.(2) The lithology of Qianjiang Formation in Qianjiang sag includes clastic rock,carbonate rock,evaporite and their mixed types,in which salt minerals come from weathered minerals and deep hydrothermal materials carried by the water system in the source area. Both conventional sandstone and unconventional migmatite in the study area have oil and gas production. The conventional sandstone reservoir has the characteristics of "source controlled enrichment,strata bound migration and sand control scale",while the unconventional migmatite reservoir has the characteristics of "sedimentary controlled block and source rock controlled horizon". The research results can provide reference for oil and gas exploration in salt lake Basin.

Reservoir characteristics and controlling factors of Permian lower He 8 member in southwestern Ordos Basin

WEI Qinlian, CUI Gaixia, LIU Meirong, LYU Yujuan, GUO Wenjie

2021, Vol.33(2): 17–25 Abstract ( 328 ) PDF (6521 KB) ( 297 )

doi: https://doi.org/10.12108/yxyqc.20210203

The Permian lower He 8 member in southwestern Ordos Basin is the main gas producing layer. In order to clarify the reservoir characteristics and controlling factors in this area,the reservoir characteristics and controlling factors of the Permian lower He 8 member were studied by means of casting thin section,scanning electron microscope,high-pressure mercury injection and reservoir physical properties. The results show that:(1) The pore types of the Permian lower He 8 member in southwestern Ordos Basin are dominated by lithic dissolved pores and intergranular pores,followed by intercrystalline micropores,and the throat radius is generally small. (2) The rock composition has an important influence on the reservoir pore structure type of the Permian lower He 8 member in the study area. The high content of quartz is conducive to the development and preservation of primary pores and has a better pore structure.(3) Diagenesis is the key factor leading to the difference in reservoir pore structure of the lower He 8 member in the study area. Compaction and cementation have a certain destructive effect on the pore structure,and they are important factors that lead to tight reservoirs in the study area. Dissolution has a positive effect on physical properties,but its improvement effect is limited. The research results can be used as a reference for fine exploration of Permian tight reservoirs in southwestern Ordos Basin.

Characteristics of breccia reservoir of Tuylock Formation of well Beixin-1 in Markit Slope of Tarim Basin

LI Huili, YOU Donghua, LI Jianjiao, TAN Guanghui, LIU Shilin

2021, Vol.33(2): 26–35 Abstract ( 358 ) PDF (9930 KB) ( 263 )

doi: https://doi.org/10.12108/yxyqc.20210204

A set of dolomite and dolomitic breccia reservoir covered by the gypsum bed of Aertashi Formation was firstly drilled in well Beixin-1 in Markit Slope of Tarim Basin,which obtained oil and gas discovery. In order to define reservoir characteristics,studies on reservoir physical properties,reservoir space,diagenesis and genesis were carried out by using the data obtained from continuous coring of the test production section. The results show that the dolomitic breccia reservoir has good reservoir physical properties,and fractures, dissolved pores and cavities are the main types of reservoir space,which mainly distributed in the brecciated silty dolomites and silty dolomites. The gypsum dissolution in the para-syngenetic period and early diagenetic stage and the tectonic rupture in Himalayan tectonic movement are the mainly constructive diagenesis. The original sedimentary environment of dolomitic breccia was limited tidal flat or lagoon, and the reservoir was developed by gypsum dissolution,and reformed by tectonic rupture during the Himalayan period.

Micro pore throat structure and its influence on seepage of Chang 8₁ tight reservoir in Nanliang-Huachi area,Ordos Basin

ZHANG Xiaohui, ZHANG Juan, YUAN Jingsu, CUI Xiaoli, MAO Zhenhua

2021, Vol.33(2): 36–48 Abstract ( 265 ) PDF (8071 KB) ( 346 )

doi: https://doi.org/10.12108/yxyqc.20210205

Chang 81 reservoir in Nanliang-Huachi area of Ordos Basin is characterized by various pore throat structures,complex seepage characteristics,unclear understanding of reservoir accumulation and oil-water relationship,which restricts the process of oil exploration breakthrough and scale development. The micro pore structure of Chang 81 reservoir in Nanliang-Huachi area was systematically studied by means of casting thin section, constant velocity mercury injection,nuclear magnetic resonance and oil-water relative permeability test,and the difference of micro pore throat structure of samples with different physical properties in the study area and its influence on oil-water seepage characteristics were compared and analyzed. The results show that:(1) The better the reservoir physical properties of the reservoir,the stronger the micro heterogeneity,the greater the movable fluid saturation, the displacement efficiency in the anhydrous period increases first, then decreases, and the higher the final water displacement efficiency.(2) When the permeability is higher than 1.000 mD,the permeability contribution mainly depends on a few connected throats with radius greater than 6.00 μm,while the permeability is lower than 1.000 mD, the permeability contribution is mainly determined by the small throats in the peak range of throats radius. (3) The pore fluid in the radius of connected throat less than 0.10 μm is immovable fluid. The better the reservoir physical properties are,the larger the pore volume controlled by the throat with the radius greater than 0.50 μm is,the higher the saturation of movable fluid is.(4) The characteristics of oil-water relative permeability in the study area can be divided into three types,among which the physical property of type I is poorest and the oil displacement efficiency is the lowest. The throat radius of type Ⅱ is 0.50-1.00 μm,and the permeability range of the two-phase is wide,the oil displacement efficiency and final oil displacement efficiency are highest in anhydrous period. The throat radius of type Ⅲ is greater than 1.50 μm,the water cut rises rapidly,the oil displacement efficiency is lowest in anhydrous period,but its final oil displacement efficiency is slightly lower than that of type Ⅱ. The distribution and connection characteristics of throat radius are one of the important factors of complex oilwater relationship in this area,which determine the permeability of reservoir and the saturation of movable fluid, affect the rule of oil-water two-phase flow,and have an important influence on oil filling,reservoir accumulation and development. The research results have certain guiding significance for analyzing oil-water relationship of lithologic reservoir and predicting favorable reservoir distribution.

Reservoir characteristics of Permian Shihezi Formation in Linxing area,Ordos Basin

YAN Min, ZHAO Jingzhou, CAO Qing, WU Heyuan, HUANG Yanzhao

2021, Vol.33(2): 49–58 Abstract ( 305 ) PDF (9621 KB) ( 349 )

doi: https://doi.org/10.12108/yxyqc.20210206

The eastern margin of Ordos Basin is a new development area,so it is very important to study the characteristics of tight reservoir and its gas control for the next exploration. Based on the analysis of logging curves,cores,cast thin section and scanning electron microscopy,the petrological characteristics,porosity, physical properties and diagenesis of tight sandstone reservoir of Permian Shihezi Formation in Linxing area of the eastern margin of Ordos Basin were studied. The results show that the reservoir porosity in the study area mainly ranges from 7% to 9%, and the permeability mainly ranges from 0.2 mD to 0.9 mD. The reservoir is dominated by micro pores,and it belongs to tight reservoir. Clay cementation and compaction are the main reasons for reservoir densification. Dissolution and the development of fractures can optimize the reservoir. When the clay mineral cement content is less than 5%,the clay mineral content is proportional to the porosity,which can protect the reservoir. Chlorite can wrap particles in a film shape to protect the reservoir. Through the study of sand body and reservoir quality index,it is considered that the natural gas reservoir in the study area is mainly controlled by sand body distribution,pore connectivity and physical properties in the vertical direction,and at the same time, fracture,and structure also have a certain impact on the gas reservoir. The research results have theoretical significance for the later development of natural gas reservoirs in the study area.

Heterogeneity characteristics of tight reservoir of lower submember of He 8 member in Su 49 block,Sulige gas field

LONG Shengfang, WANG Yushan, LI Guoliang, DUAN Chuanli, SHAO Yingming, HE Yongmei, CHEN Lingyun, JIAO Xu

2021, Vol.33(2): 59–69 Abstract ( 315 ) PDF (6515 KB) ( 258 )

doi: https://doi.org/10.12108/yxyqc.20210207

Typical tight sandstone reservoirs are developed in lower submember of He 8 member in Su 49 block, Sulige gas field. The gas-water distribution rules are complex and the gas production of single well varies greatly. In order to clarify the influence of reservoir heterogeneity on gas reservoir distribution and gas well productivity, and to achieve efficient development of gas field,based on fine stratigraphic division and comparison,the systematic research on reservoir and plane heterogeneity was carried out by making full use of the data of drilling and logging,testing analysis and gas well production. The results show that:(1) The heterogeneity of lower submember of He 8 member in the study area is relatively strong. The reservoir physical properties of lower sand group 2 of He 8 member are generally poor,there are many interlayers in the layer,and the vertical and plane connectivity of sand body is poor,and its heterogeneity is stronger than that of lower sand group 1 of He 8 member.(2) On the plane,the interlayer and plane heterogeneity in the west of the study area are strong,the sand body connectivity of lower sand group 1 of He 8 member in Su 176 area and nearby is good,and there are relatively high porosity and permeability zones with less interlayer,which is favorable for natural gas enrichment and accumulation.(3) Reservoir heterogeneity has obvious influences on gas-bearing property,macro distribution of gas reservoir and development effect. Relatively good reservoir physical property,connectivity and less interlayer are the key to gas enrichment and high production. The results can provide reference for well location deployment and later development in the study area and similar areas.

Reservoir characteristics and main controlling factors of Ordovician Yangshuiwu deep buried hill in Jizhong Depression

HUANG Yun, YANG Dexiang, LI Yubang, HU Mingyi, JI Hancheng, FAN Jie, ZHANG Xiaofang, WANG Yuanjie

2021, Vol.33(2): 70–80 Abstract ( 281 ) PDF (10180 KB) ( 290 )

doi: https://doi.org/10.12108/yxyqc.20210208

Strong reservoir heterogeneity and their unclear controlling factors are essential factors which restrict the exploration of Ordovician Yangshuiwu deep-buried hill. Based on core and thin-section observations and bulk XRD analysis,combined with scanning electron microscopy(SEM),physical properties,FMI and Sr isotope,the reservoir characteristics and their main controlling factors in the study area were analyzed. The results show that there are three sets of stratiform continuous reservoir and one set of locally discontinuous reservoir in vertically from the bottom to the top of the Ordovician buried hill. The first set of reservoir is mainly distributed in Liangjiashan Formation and the first members of Majiagou Formation,the second set of reservoir is distributed on the third members of Majiagou Formation to the top of the second member of Majiagou Formation,and the third set of reservoir is distributed on the fifth member of Majiagou Formation to the top of the forth member of Majiagou Formation. The sedimentary facies of the reservoirs is dominated by tidal flat facies,the lithology is mainly mudsilty dolomite,and the reservoir space consists of intercrystalline pores,intercrystalline dissolved pores,structural micro-fractures and expanded dissolved fractures. The porosity varies from 0.7% to 7.2% with an average of 3.26%,and the permeability ranges from 0.08 mD to 7.79 mD with an average of 1.49 mD,which suggests the reservoirs are characterized by extremely low porosity and extremely low permeability. The three sets of stratiform reservoir are controlled by dolomitization,karstification and tectonism. Dolomitization is the basic condition for reservoir formation,karstification is an important factor for reservoir improvement,and tectonism is a key factor for the formation of oil-bearing reservoirs. The first set of the reservoir is mainly controlled by interlayer karst and buried dolomitization,the second set of reservoir is mainly controlled by seep-reflux dolomitization and buried dolomitization, and the third set of reservoir is mainly controlled by seep-reflux dolomitization, meteoric water leaching and fractures. The third set and the first set of reservoirs are the most favorable reservoirs with deep dolomitization,large dolomite thickness,strong karst transformation and good physical properties,followed by the second set. Locally discontinuous reservoirs are related to tectonic activities,and mainly affected by faults, tectonic fractures and hydrothermal dolomitization.

Characteristics and genetic mechanism of Mesozoic clastic reservoirs in Beidagang buried hill,Huanghua Depression

LI Zubing, CUI Junfeng, SONG Shunyao, CHENG Yabin, LU Yi, CHEN Cen

2021, Vol.33(2): 81–92 Abstract ( 290 ) PDF (8669 KB) ( 287 )

doi: https://doi.org/10.12108/yxyqc.20210209

The characteristics and genetic mechanism of Mesozoic clastic reservoirs in Beidagang buried hill, Huanghua Depression were systematically analyzed by combining the data of core,X-ray diffraction,casting thin section,scanning electron microscope and logging with the burial evolution history of the strata. The results show that:(1) There are many types of Mesozoic clastic rocks in the study area,but they are mainly feldspathic lithic sandstone,lithic quartz sandstone and lithic sandstone.(2) The Mesozoic clastic reservoirs in the study area are composed of primary pores,secondary dissolved pores and micro-fractures,dominated by secondary dissolved pores. The reservoir properties are characterized by low porosity and low to extra low permeability.(3) Reservoir development is influenced by sedimentary,diagenetic and tectonic processes. Compaction,cementation,dissolution and oil and gas charging in diagenetic process all have effects on reservoir development,among which dissolution has the greatest impact on the development of reservoir space. From the control degree of reservoir development,the sorting of rock particles is stronger than lithology,and compaction is stronger than cementation. The slope,unconformity surface and fault caused by tectonic action not only provide the place for the dissolution,but also provide channel for the flow of the dissolution fluid. The research results provide a geological basis for the optimization of favorable exploration target areas in Beidagang buried hill area of Huanghua Depression.

Formation mechanism and petroleum geological significance of Paleogene sandstone with high natural gamma value in Zhuyi Depression, Pearl River Mouth Basin

XIANG Qiaowei, LI Xiaoping, DING Lin, DU Jiayuan

2021, Vol.33(2): 93–103 Abstract ( 358 ) PDF (8559 KB) ( 305 )

doi: https://doi.org/10.12108/yxyqc.20210210

It is an unconventional means of oil and gas exploration to use radioactive elements to search for oil and gas. In recent years,sandstones with high natural gamma (GR) value (100-300 API) have been drilled in Paleogene around the hydrocarbon-rich depression in Zhuyi Depression,Pearl River Mouth Basin,and the GR value is even higher than that of mudstone in the same area(100-200 API). In order to understand the geological significance behind this special phenomenon,the correlation trend line analysis of the contents of uranium (U), thorium (Th) and potassium (K) with GR value was carried out for the Paleogene sandstone with high GR value in Pearl River Mouth Basin. The main reasons and genetic mechanism of the increase of GR value of sandstone were analyzed from the characteristics of well seismic,lithology and mineral composition,and the accumulation conditions,migration channels,driving forces and hydrocarbon significance of radioactive elements were discussed. The results show that the GR value of sandstone is higher in Xijiang and Huizhou areas due to the increase of U content,and higher in Enping and Panyu areas due to the increase of K and Th content. There are two genetic mechanisms for the increase of GR value of sandstone. One is that the enrichment of radioactive element ion U4+ brought by underground fluid at oxidation-reduction surface leads to the high GR value of formation. This special phenomenon shows that the enrichment of U4+ indicates the existence of oil and gas in traps near large faults with connected basement,which confirms the effectiveness of oil and gas migration channels in the study area and has very important guiding significance for the prediction of oil and gas reservoirs. The other is that the massive deposition of minerals containing radioactive elements brought by surface fluids leads to the high GR value of strata and unstable properties of minerals containing radioactive elements,which can indicate the existence of near-source supply,and is of great significance for judging the provenance and sedimentary environment. The research results provide a basis for predicting favorable zones for hydrocarbon accumulation in the study area.

Tectonic evolution and formation mechanism of Davie Fracture Zone in East Africa coast

QIN Yangliang, HE Youbin, CAI Jun, LI Hua, ZHANG Can, LIU Jianning

2021, Vol.33(2): 104–115 Abstract ( 269 ) PDF (6857 KB) ( 248 )

doi: https://doi.org/10.12108/yxyqc.20210211

The north-south-trend length of Davie Fracture Zone along the East African coast was comprehensive analyzed based on East African coast topography,free air gravity anomalies and magnetic anomalies. The structural characteristics of different parts of Davie Fracture Zone were clarified through fine interpretation of seismic data. The structural characteristics of the Davie Fracture Zone in different periods were analyzed by means of layer flattening,growth index and balanced profile,combined with regional dynamic analysis. The results show that the horizontal distribution of Davie Fracture Zone is between 4°S and 22°S from north to south. The vertical struture has different characteristics of north-south segmentation,and structural ridges can be seen in the southern section,accompanied by typical undercut structures,and in the northern section,positive inverted structures can be seen. Affected by the differential activities of the plates in the East African coast,the Davie Fracture Zone has different characteristics in different periods. In Late Carboniferous to Early Jurassic,the Davie Fracture Zone was mainly affected by tensile stress,and typical graben structures can be seen in the flattened seismic section. During the Middle Jurassic-Early Cretaceous,it turned into strike-slip property due to the southward drift of Madagascar. Since the Late Cretaceous,it entered the passive continental margin stage,and the Davie East Fault basically ceased its activity,while the Davie West Fault continued to be active. The development and evolution of the Davie Fracture Zone is inherited,and its north-south structural difference is the result of the combined effect of heat conduction and plate stress transition. Thus,a tectonic deformation model of "continuous activity of the southern structural ridge and local compression after the northern expansion" was established. The above conclusions could make a contribution for the study of oil and gas geology of the Davie Fracture Zone.

Reservoir characteristics and main controlling factors of Lucaogou Formation in Jimsar Sag,Jungger Basin

ZHANG Zhiheng, TIAN Jijun, HAN Changcheng, ZHANG Wenwen, DENG Shouwei, SUN Guoxiang

2021, Vol.33(2): 116–126 Abstract ( 434 ) PDF (12578 KB) ( 389 )

doi: https://doi.org/10.12108/yxyqc.20210212

In order to study the characteristics and main controlling factors of shale oil reservoir of Lucaogou Formation in Jimsar Sag,core observation,cast thin section identification,scanning electron microscope analysis and whole rock analysis were carried out,and petrological characteristics,physical properties and diagenesis were studied. The results show that the rock types of Lucaogou Formation are mainly clastic rocks,carbonate rocks and mixed fine-grained rocks,with low compositional maturity and structural maturity,medium sorting. Primary intergranular pores and secondary dissolved pores are the main reservoir space. The average porosity of sandstone is 7.34%,and the average permeability is 0.079 mD. It belongs to low permeability tight reservoir. Reservoir development is mainly controlled by sedimentation and diagenesis. Sedimentation controls the development and distribution of reservoir rock types. Compaction and cementation are the main reasons for the decrease of reservoir porosity in the process of diagenesis,and dissolution plays a certain role in improving reservoir physical properties. The reservoirs of Lucaogou Formation have experienced three densification stages. Compaction is the main reason for early densification. Continuous compaction and siliceous cementation play a leading role in middle-term densification. Late compaction,carbonate and clay mineral cementation jointly act on the reservoir to further densify the reservoir. The research results can provide a theoretical basis for the study of of shale oil development in Lucaogou Formation of Jimsar Sag.

EXPLORATION TECHNOLOGY

Application of seismic and microseismic data fusion technology in postfracturing evaluation of shale oil reservoir

DU Jinling, LIN He, JI Yongjun, JIANG Hong, XU Wenli, WU Shunwei

2021, Vol.33(2): 127–134 Abstract ( 320 ) PDF (4320 KB) ( 239 )

doi: https://doi.org/10.12108/yxyqc.20210213

Shale oil is a key point of unconventional oil and gas exploration and development in recent years,and its exploration and development are characterized by high risk,high investment and high difficulty. In order to maximize the economic benefits of a single well,it is necessary for multidisciplinary personnel to cooperate to improve the identification ability of sweet spots. 3D seismic can be used to predict reservoir in space,and microseismic monitoring results can be used to directly evaluate the effect of hydraulic fracturing, so the fusion technology of micro-seismic and 3D seismic data can improve the prediction accuracy of sweet spots. Based on the fusion of surface seismic attributes and micro-seismic results,combined with oil and gas productivity,the main factors affecting oil and gas productivity were analyzed. The results show that the properties of coherence value,ant body, amplitude, brittleness and horizontal stress difference are directly related to the shape of artificial fracture network in Jimsar Sag,which can affect the effect of reservoir stimulation. Based on the sweet spots identification method of multi-attributes fusion,the areas with low coherence value,weak amplitude,high brittleness and low horizontal stress difference was optimized,and the study area was divided into three types of sweet spots areas. The research results can provide a basis for well trajectory optimization and the optimized project design for reservoir stimulation.

Identification method of shale lithofacies by logging curves: a case study from Wufeng-Longmaxi Formation in Jiaoshiba area,SW China

YANG Yang, SHI Wanzhong, ZHANG Xiaoming, WANG Ren, XU Xiaofeng, LIU Yuzuo, BAI Luheng, CAO Shenting, FENG Qian

2021, Vol.33(2): 135–146 Abstract ( 484 ) PDF (3830 KB) ( 552 )

doi: https://doi.org/10.12108/yxyqc.20210214

Identification of shale lithofacies is the basis of shale gas exploration and development. Different types of shale have different material components and textures,and thus the brittleness and physical properties are different. At present,the study on shale lithofacies identification by logging curves is relatively weak. Based on logging data and core test data of three wells from Wufeng-Longmaxi Formation in Jiaoshiba area,through multi-parameter optimization and multivariate linear fitting,the prediction equations of relative content of clay minerals and siliceous minerals were established respectively,and the identification method of shale lithofacies by logging curves was discussed. The results show that argillaceous shale lithofacies has the characteristics of high DEN,CNL,K,KTh,and low U,U/Th,the mixed shale lithofacies has the characteristics of middle DEN, CNL,K,KTh,U,U/Th,and siliceous shale lithofacies has the characteristics of high U,U/Th and low DEN, CNL,K,KTh. Furthermore,a radar chart for shale facies identification was established. After corresponding processing,the logging curve values corresponding to different lithofacies have different distribution ranges in the chart. The chart can effectively identify shale lithofacies and correct the lithofacies identified by the prediction equation. The predicted results are in agreement with the measured values. Combining quantitative identification of lithofacies by prediction equation and qualitative identification of lithofacies by radar chart,shale lithofacies of Wufeng-Longmaxi Formation in Jiaoshiba area can be well identified through double constraints.

OIL AND GAS FIELD DEVELOPMENT

Microscopic characteristics of remaining oil distribution and quantitative characterization of its producibility

WANG Lihui, XIA Huifen, HAN Peihui, CAO Ruibo, SUN Xianda, ZHANG Siqi

2021, Vol.33(2): 147–154 Abstract ( 339 ) PDF (3881 KB) ( 416 )

doi: https://doi.org/10.12108/yxyqc.20210215

At present,there are some problems in the quantitative characterization of microscopic remaining oil, such as large gap between macro and micro analysis results,unclear image and relatively few analysis methods. In view of the above problems,by means of core displacement experiment,frozen slicing technology and core fluorescence analysis system,the distribution characteristics and producing degree of microscopic remaining oil in different displacement modes,different core positions and different types were analyzed. The results show that the ratio of remaining oil in injection end,middle end and produced end of core increases in turn. After water flooding,the remaining oil is mainly in free state and bound state,accounting for 93.65% in total,and only 6.35% in semi bound state. Polymer flooding has obvious effect on remaining oil with cluster,intergranular adsorption,thin film on pore surface and corner. After ASP flooding,the proportion of remaining oil with granular adsorption and intergranular adsorption is high. There is little difference between the results of fluorescence analysis and core flooding experiment, which verifies the correctness of the analysis results

Influence of pore throat size distribution on oil displacement by spontaneous imbibition in tight oil reservoirs

WANG Fuyong, YANG Kun

2021, Vol.33(2): 155–162 Abstract ( 252 ) PDF (2827 KB) ( 286 )

doi: https://doi.org/10.12108/yxyqc.20210216

Spontaneous imbibition is an important development mechanism for tight oil reservoirs. It is of great significance to develop a correct mathematical model of spontaneous imbibition to clarify the law of oil production with spontaneous imbibition. Based on the capillary model,considering the distribution of irreducible water and residual oil saturation,using the two-dimensional Gaussian distribution function to fit the pore throat size distribution of tight sandstone obtained from high-pressure mercury intrusion,a core-scale mathematical model for oil displacement with spontaneous imbibition in a tight sandstone matrix was constructed,and verified with imbibition experiment. The influencing factors of imbibition law were analyzed to clarify the effects of pore throat distribution,wetting angle and interfacial tension on the oil production rate by spontaneous imbibition. The results show that the distribution of micro and nano pore throats in tight sandstone has the characteristics of two-dimensional Gaussian distribution in the semi-log plot. In the early stage of spontaneous imbibition,the imbibition rate mainly depends on the distribution of large pores,and the larger the core permeability is,the greater the imbibition and displacement rate is. In the middle and later stage of spontaneous imbibition,the imbibition rate is mainly affected by nanopores. The imbibition rate increases with the decrease of wetting angle,the increase of interfacial tension between oil and water and the decrease of oil viscosity. It can accurately predict the imbibition rate of tight reservoir by defining the pore throat distribution characteristics,which has a certain guiding role in determining the production system of tight reservoirs.

New production index curve of fractured-vuggy carbonate reservoirs

YANG Meihua, ZHONG Haiquan, LI Yingchuan

2021, Vol.33(2): 163–170 Abstract ( 241 ) PDF (1970 KB) ( 518 )

doi: https://doi.org/10.12108/yxyqc.20210217

The production index curve of elastic drive reservoir has always been regarded as a straight line. Because oil compressibility is a variable that decreases as formation pressure increases,the production index curve is not a straight line but a curve,which deviates from straight line more significantly as reservoir pressure drop increases. Especially for deep buried fractured-vuggy carbonate reservoirs which have large pressure difference between formation pressure and oil saturation pressure,the production index curve of reservoir will produce obvious error, hence it needs to be improved. By creating the power function relationship between oil volume factor,oil compressibility and formation pressure,the material balance equation of elastic drive fractured-vuggy carbonate reservoir was simplified,and a new production index curve of reservoir was established. The results show that the relationship between oil volume factor and formation pressure above saturation pressure is not linear but accords with power function,and the power function relationships between oil volume factor,oil compressibility and formation pressure not only conform to the actual law but also have high computational accuracy. There are two cases for using oil compressibility:one is the oil compressibility at a certain formation pressure,the other is the average oil compressibility in a certain formation pressure range,the two cases cannot be mixed,and material balance equation should adopt the latter. The new production index curve of elastic drive reservoirs is always a straight line,and the slope of the line is just original oil in place. Therefore,the new production index curve of reservoir is conducive to reservoir research,such as accurately judging the driving type of a reservoir and calculating the reserves.

Difference analysis of isosteric heat of methane adsorption on shale based on fugacity and pressure: a case study of Yanchang Formation in Yanchang exploration area

XUE Pei, ZHANG Lixia, LIANG Quansheng, SHI Yi

2021, Vol.33(2): 171–179 Abstract ( 247 ) PDF (3103 KB) ( 395 )

doi: https://doi.org/10.12108/yxyqc.20210218

In order to improve the calculation method of isosteric heat of adsorption,clarify the thermodynamic characteristics of adsorption of CH4 by continental shale and reveal its adsorption mechanism,shale samples from Yanchang Formation in Yanchang exploration area were selected to carry out isothermal adsorption experiment of CH4 adsorption on shale at different temperatures,and the difference of isosteric heat of adsorption based on fugacity-absolute adsorption capacity and pressure-absolute adsorption capacity was analyzed by using absolute adsorption capacity curve. The results show that:(1) Fugacity is less than pressure,and in the pressure range of 0.36-2.21 MPa,the difference between fugacity and pressure is small. With the temperature decreasing and the pressure increasing,the difference increases.(2) The isotherm curves based on fugacity and pressure have obvious monotonic increasing linear characteristics,but the slope of isosteric heat of adsorption curve obtained by pressure-absolute adsorption capacity is larger than that obtained by fugacity-absolute adsorption capacity,which indicates that the intermolecular force of adsorbate has a great influence on the calculation results of isosteric heat of adsorption based on pressure-absolute adsorption capacity.(3) In the absolute adsorption capacity range of 0.01-0.35 mmol/g,the relative deviation of isosteric heat of adsorption obtained based on fugacity-absolute adsorption capacity and pressure-absolute adsorption capacity is -86.54%-57.01%. The data of fugacityabsolute adsorption capacity should be used as the basic data for the calculation of isosteric heart of adsorption in the thermodynamic evaluation of shale gas adsorption system.

PETROLEUM ENGINEERING

Re-discussion on principle of constant porosity during primary deformation of rock

ZHU Suyang, LI Dongmei, LI Chuanliang, LI Huihui, LIU Xiongzhi

2021, Vol.33(2): 180–188 Abstract ( 383 ) PDF (3828 KB) ( 286 )

doi: https://doi.org/10.12108/yxyqc.20210219

In the primary deformation of reservoir rocks,the assumption that the shape of the skeleton particles remains unchanged assumes that the porosity of the rocks remains unchanged during the compression process. However,the shape of the skeleton particles does not strictly remain unchanged. In order to study the influence of the shape change of skeleton particles on porosity,based on the elastic deformation model,finite element numerical simulation method was used to study the deformation of skeleton particles and its influence mechanism on porosity during the primary deformation of porous media. The results show that the displacement of skeleton particles is small in the constraint direction(particle contact position),and it is larger in the unconstrained direction (pore position),which changes the shape of the particles,reduces the porosity of rock. However,the young's modulus of rock minerals is larger,and the constraint conditions of the rock skeleton particles are more demanding than those in numerical experiments. Therefore,the effect of skeleton particle deformation on porosity is very weak. In the numerical experiments,rigid epidermis has only a certain effect on the initial porosity value. However,the flexible skin in the core gripper has a great influence on the measurement process,which is the direct cause of the great change of porosity in the experiment. Therefore,in the process of reservoir production, the deformation process of rock can still be considered to follow the "porosity invariance principle".