Lithologic Reservoirs

The provenance of Paleogene is complex in the northern steep slope zone of Huanghekou Sag,and the reservoir physical properties are quite different. The data of cores,thin section,logging,3-D seismic and physical properties were used to reveal the provenance of Paleogene,and the controlling effect of the paleo-prov-enance on high-quality reservoir was discussed. The results show that:(1)Paleo-gullies were commonly developed in the study area. During the sedimentary period from the Es to Ed,the lithology and area of the parent rock changed significantly,and the area of the provenance experienced the evolution process of "large-smalllarge".(2)The denudation stage of the paleo-provenance had obvious control effect on the sand body. In the longitudinal direction,in Es3,the range of the provenance was large. In the provenance,a large number of Mesozoic clastic rocks participated in the source,and the sedimentary area formed a thin layer of glutenite with a small thickness. In Es 2,the provenance was large. The source was mainly volcanic rock erosion. The sedimentary area formed thick glutenite with a large thickness. In Es1,a rapid lake invasion occurred. The range of the provenance was reduced. The thin layer of glutenite formed in the sedimentary zone had a small thickness. In Ed3,a lake retreat occurred. The area of the provenance expanded. There were a large number of mudstones formed in Es1 to participate in the supply. The sedimentary area formed a thin layer of glutenite with a small thickness. On the plane, during the same deposition period,the valley system in the western and eastern section of the eastern part of the provenance was large. The provenance was dominated by volcanic rocks and granite erosion. The glutenite which formed in the sedimentary area was large in thickness and scale. The western section of the eastern part was dominated by carbonate rock erosion,and the glutenite formed in the sedimentary area was small in thickness and scale.(3)The parent rock had obvious control effected on reservoir physical properties. From Es3 to Ed3,the eastern section of the eastern part was dominated by volcanic rock erosion,and the buried depth was shallow. The reservoir contained a large number of volcanic rock cuttings,which were easy to dissolve in the later stage,and were weak in cementation and good in reservoir properties. The western section of the eastern part was mainly characterized by carbonate rock erosion and shallow depth,but the cementation was strong and the physical properties were poor. The burial was deep in the west,the compaction and cementation were strong,and the reservoir properties were poor. Therefore,in the similar depth section,when the carbonate parent rock was supplied,the reservoir in the sedimentary area contained a large amount of carbonate gravel and cuttings,and the interstitial material was mainly calcareous cement,with strong cementation and poor physical properties. When volcanic rocks and metamorphic granites were supplied,the reservoir in the sedimentary area was mainly volcanic rocks or granite gravel and cuttings. The content of calcareous cement was less,the cementation was relatively weak,and the reservoir properties were better overall. This result can provide reference for further exploration and evaluation in the study area.

Sedimentary characteristics and geological significance of earthquake events of Sha 3 member in Huimin Sag,Jiyang Depression

LIU Jianning, HE Youbin, WANG Ning, GU Zhixiang, HAO Ting, LIU Yawei

2020, Vol.32(2): 14–23 Abstract ( 336 ) PDF (6205 KB) ( 547 )

doi: https://doi.org/10.12108/yxyqc.20200202

In order to study the sedimentary characteristics of paleoearthquake events in the third member of Shahejie Formation in Huimin Sag of Jiyang Depression and its reservoir controlling effect,core observation,vertical sequence division of single well of seismic sedimentary rocks,analysis of main controlling factors of sedimentation and geological significance of paleoearthquake events were carried out. The results show that:(1)The structure of seismites is very well developed in the third member of Shahejie Formation in Huimin Sag, including shatter crack, autoclastic breccia,stepped small fault,liquefied vein,liquefied curl,liquefied breccia and other brittle plastic deformation structures.(2)Seismic intensity,sediment consolidation degree and terrain slope are the main factors affecting the development of seismites. The vertical sedimentary sequence of several wells shows that the development characteristics of seismites in different structural positions in the study area are different, which can be divided into four areas,namely near source gentle area,main seismic area,near source slope area and far source gentle area.(3)The study of earthquake event deposition provides a basis for the determination of fault activity rate, growth index and other parameters in Huimin Sag,and the seismic event is an important power source for stimulating the secondary migration of sand body. The vibration in seismic event can cause the particle rearrangement of unconsolidated sediments,and reduce the heterogeneity of the reservoir in the third member of Shahejie Formation.(4)The abundant brittle seismites near faults may be the auxiliary channel of oil and gas migration,the autoclastic breccia formed by earthquakes is a good reservoir,and the compacted layer with uniform liquefaction is a high-quality caprock. The results of this study are of great significance to seismic exploration in Huimin Sag.

Carbonate cementation characteristics and genetic mechanism of tight sandstone reservoirs in Longdong area,Ordos Basin

SHEN Jian

2020, Vol.32(2): 24–32 Abstract ( 359 ) PDF (4657 KB) ( 538 )

doi: https://doi.org/10.12108/yxyqc.20200203

In order to study the carbonate cementation characteristics and its genetic mechanism in fine-grained tight sandstone reservoirs in Longdong area of Ordos Basin,thin section analysis,scanning electron microscopy and fluid inclusion test were carried out. The results show that:(1)Carbonate cements are widely developed in tight sandstones of Longdong area,Ordos Basin,with an average volume fraction of 4.2%,and are mainly composed of ferrocalcite and ankerite.(2)Most of the carbonate cements precipitate in the form of pore or enlarged edge,and the homogenization temperature of fluid inclusions is higher(the peak value is 100-110℃),and the formation stage is generally later.(3)Calcium ion sources of ferrocalcite and ankerite cements are closely related to feldspar dissolution and clay semi-permeable membrane effect in Chang 7 sandstone,while iron and magnesium ion sources are controlled by the alteration of mica and tuffaceous and the dissolution of dolomite debris and metamorphic debris.（4）The distribution of dolomite debris in clastic components controls the differential precipitation of ferrocalcite and ankerite cements in plane，and ankerite cements only occur in sandstones rich in dolomite debris.（5）Carbonate cementation is an important factor for pore loss in late tight oil sandstone. After strong compaction，the residual pores are gradually filled by carbonate cements. When the volume fraction of carbonate cements is more than 2%，the effect of cementation on reducing pore size is obvious. The research results have certain guiding significance for predicting favorable reservoir distribution in Longdong area.

Characteristics and controlling factors of Lower Paleozoic reservoir in Sulige Gas Field

TIAN Qinghua, LIU Jun, ZHANG Chen, WANG Wensheng, HUANG Dan

2020, Vol.32(2): 33–42 Abstract ( 374 ) PDF (8937 KB) ( 423 )

doi: https://doi.org/10.12108/yxyqc.20200204

The reservoir of Lower Paleozoic Majiagou Formation in Sulige Gas Field has become a strong support for stable production of the gas field. It is of great significance to analyze the reservoir characteristics and control factors for maintaining stable production of the gas field. The main reservoir characteristics of Majiagou Formation were analyzed by means of core observation,thin section identification and cathodoluminescence. The results show that the reservoir of Majiagou Formation is mainly granular crystalline dolomite,grain crystalline dolomite and microbiological rock. The reservoir pores are mainly intercrystalline pore,intercrystalline dissolved pore,gypsum mould pore,miniature dissolved holes,intergranular pores. Reservoir distribution is mainly controlled by karstification and paleogeomorphic distribution. Epidiagenetic karstification in the Caledonian period has little contribution to the reservoir,even a destructive effect. The high part of karst palaeogeomorphology is mainly affected by epidiagenetic karstification,which has a certain transformation effect on the reservoir space and connectivity,resulting in better reservoir physical properties and high gas production per well,while the low part of karst palaeogeomorphology is mainly affected by the karstification in the quasi-contemporaneous period, with relatively poor physical properties and low gas production per well. The research results can provide geological basis for the prediction of favorable areas of Lower Paleozoic gas reservoirs in Sulige Gas Field.

Characteristics of weathering crust karst reservoir of Deng 4 member in Moxi area,Sichuan Basin

YANG Fan, LIU Lifeng, RAN Qiquan, KONG Jinping, HUANG Suqi, HUANG Changwu

2020, Vol.32(2): 43–53 Abstract ( 279 ) PDF (10604 KB) ( 319 )

doi: https://doi.org/10.12108/yxyqc.20200205

In recent years,great breakthroughs have been made in oil and gas exploration of Deng 4 member in Moxi area,Sichuan Basin. In order to study the characteristics and distribution regularity of high-quality karst reservoirs in the upper sub-member of Deng 4 member in Moxi 22 well area,core analysis,physical property testing,seismic data interpretation,logging data analysis and prediction of favorable development area of karst reservoir were carried out. The results show that:(1)The lithology of karst reservoir is mainly algal dolomite, sand-clastic dolomite and crystalline dolomite,and the reservoir space is mainly dissolved pore,cave and fracture.(2)The dissolution of carbonate rock includes the contemporaneous dissolution of atmospheric fresh water, deep hydrothermal dissolution and organic acid dissolution in the burial period,and dissolution of atmospheric fresh water in the supergene period.(3)The supergene dissolution controls the distribution of high-quality reservoirs which are mostly developed near the vertical vadose zone and the upper part of horizontal phreatic zone. The distribution of high-quality reservoirs in plane is controlled by sedimentary facies belt and palaeogeomorphological characteristics,with mound-beach facies and karst dome being the best. The research results indicate the direction for the next exploration in Moxi area.

Characteristics and sedimentary models of diamictite in saline faulted lacustrine basin: a case study of Fu 2 member in Jinhu Sag,Subei Basin

HUANG Jianling, FU Qiang, QIU Xuming, ZHAO Shijie, LI Linxiang

2020, Vol.32(2): 54–66 Abstract ( 433 ) PDF (10671 KB) ( 422 )

doi: https://doi.org/10.12108/yxyqc.20200206

In order to clarify the sedimentary characteristics of diamictiteinsaline faulted lacustrine basin,by means of core observation,core slice identification,X-ray diffraction to whole-rock mineral analysis test and other technical means,the diamictite of the second member of Eocene Funing Formation in Jinhu Sag was studied. The results show that:(1)Diamictite is dominated by feldspar quartz minerals,calcite(dolomite)minerals and clay minerals. It can be divided into four types:feldspar-quartz diamictite, calcite(dolomite) diamictite,clayey diamictite and pure-diamictite.(2)According to the sedimentary characteristics of the saline faulted lacustrine basin in the Jinhu Sag,a mixed sedimentary model of "shallow water to deep water and multi-factor control" was established. In the saline faulted lacustrine basin,the deposition of diamictite is mainly controlled by source supply,fault activityand sedimentary environment changes. Under the active fault control,the terrigenous debris is continuously supplied to the interior of the lacustrine basin, and the sedimentary type is dominated by interfacial mixed sedimentation and intermittent mixed sedimentation. As the fault activity tends to stable,sedimentary environment changes,transgression increases,the sediment of terrigenous debris is limited, and the sedimentary type is dominated by maternal mixed sedimentation. The research results have certain enlightenment significance for the exploration of deep-water tight reservoirs in the continental lacustrine basin.

Geological conditions and exploration potential of shallow oil and gas in slope area of Mahu Sag,Junggar Basin

HU Xiao, QU Yongqiang, HU Suyun, PAN Jianguo, YIN Lu, XU Duonian, TENG Tuanyu, WANG Bin

2020, Vol.32(2): 67–77 Abstract ( 397 ) PDF (11478 KB) ( 369 )

doi: https://doi.org/10.12108/yxyqc.20200207

Shallow layer(T2 k-J)in the slope area of Mahu Sag in Junggar Basin has great exploration potential. In order to study the geological conditions of oil and gas and the distribution law of favorable area for reservoir formation,a large number of analyses of mud-logging,wire-logging and core data were carried out. Based on 3D seismic data interpretation,the shallow layers in the slope area were comprehensively evaluated. The results show that:(1)The reservoirs of Karamay Formation,Baijiantan Formation,Badaowan Formation and Sangonghe Formation in the slope area of Mahu Sag are characterized by large scale,shallow burial,good physical properties,and have the conditions to form lithologic reservoirs with cluster distribution.(2)The reservoir cap assemblage in the study area is well configured and vertically overlapped,which lays a good reservoir cap assemblage condition for lithologic reservoirs with cluster distribution.(3)The development of faults in the slope area provides a good oil-gas migration channel for shallow reservoirs in the slope area.(4)Fault blocks or fault lithologic traps in the study area have the characteristics of cluster distribution,and they are overlapped and contiguous in space,with superior conditions for trap forming. The shallow and deep oil and gas enrichment zones are characterized by "relay accumulation" and have certain inheritance. The research results have a guiding role for shallow exploration in the slope area of Mahu Sag.

Distribution and evaluation of underwater distributary channel sandstone reservoir based on well-seismic combination: a case study of JP₃⁵ sand group in Shifang gas reservoir

LI Hongtao, MA Liyuan, SHI Yunqing, HU Xiangyang, GAO Jun, LI Hao

2020, Vol.32(2): 78–89 Abstract ( 312 ) PDF (10324 KB) ( 542 )

doi: https://doi.org/10.12108/yxyqc.20200208

In order to evaluate the potential and optimize favorable zones of gas reservoir of the third member of Penglaizhen Formation in Shifang area, western Sichuan,joint calibration method of core data,log data and seismic data were used to analyze the sedimentary facies,reservoir characteristics and favorable gas-bearing reservoir distribution of the gas reservoir and JP35 sand group. The results show that the gas reservoir can be further divided into five sand groups,and the thickness of each sand group is stable. The tectonic setting was stable and the strata were gentle during the sedimentary period. The sediment belongs to shallow-water river-controlling delta front, and the underwater distributary channel is the most favorable sedimentary microfacies. The reservoir rock of JP35 sand group is dominated by of medium-low porosity and ultra-low permeability dissolved fine-grained lithic sandstone,with poor seepage capacity,which is an important factor affecting reservoir quality evaluation. The comprehensive analysis results of reservoir distribution and gas-bearing property based on well-seismic combination show that,compared with the distribution of underwater distributary channel sand bodies,the distribution range of high-quality effective gas-bearing reservoirs is relatively limited with the characteristics of discontinuous bands,and its distribution is controlled by sedimentary microfacies,distributary channel scale and local high part of the structure. This method and research results can provide reference for analyses of sedimentary facies, reservoir characteristics,distribution and evaluation of the study area and similar areas,as well as the optimization of favorable zones.

Classification and effectiveness evaluation of karst reservoirs of Maokou Formation in eastern and southern Sichuan Basin

WU Feng, XI Yanping, ZHANG Ya, CHEN Shuangling, YAO Cong, YANG Yuran

2020, Vol.32(2): 90–99 Abstract ( 315 ) PDF (7445 KB) ( 342 )

doi: https://doi.org/10.12108/yxyqc.20200209

Influenced by exposure and weathering leaching,Maokou Formation of the middle Permian in eastern and southern Sichuan Basin has developed unique eogenetic weathering crust karst reservoirs,which has great exploration and development potential. Due to the complex characteristics of the pore structure,vertical and horizontal distribution and well logging response,it is difficult to carry out logging effectiveness evaluation. On the basis of reservoir classification,combined with karst development model,the logging effectiveness evaluation methods for three sets of typical reservoirs of Maokou Formation were studied. The results show that:(1)The effectiveness of the reservoirs developed in the top of Maokou Formation is closely related to the filling degree of weathering residual deposits such as auxetic mudstone. The effectiveness of the reservoirs with higher uranium content in Mao 1 member to Mao 3 member is closely related to the activity of the formation water,and the effectiveness of bedded reservoirs developed in Mao 1 member to Mao 2 member is closely related to the control of the argillaceous limestone on the water table.(2)The radioactive intensity of rocks directly or indirectly reflects the development and effectiveness of the karst reservoirs in Maokou Formation,so natural gamma ray logging and natural gamma ray spectral logging play important roles in the evaluation of the effectiveness of karst reservoirs.(3)Influenced by lithology,fault,karst erosion degree and other factors,the distributions of horizontal undercurrent zone and deep slow current zone vary in different structures,and the main developed depth of reservoirs is also different. The study results can be used for reference for the validity identification of karst reservoirs.

Analysis of electrical characteristics of tight sandstone reservoirs

HOU Zhenxue, CHEN Zhen, NIU Quanbing, SONG Guangjian, LIU Yanbin

2020, Vol.32(2): 100–107 Abstract ( 406 ) PDF (5033 KB) ( 358 )

doi: https://doi.org/10.12108/yxyqc.20200210

In order to clarify the complex electrical characteristics of tight sandstone reservoirs,the electrical characteristics of tight sandstone reservoirs of Permian upper Shihezi Formation in L block in the eastern margin of Ordos Basin were analyzed based on high resolution array induction data,combined with nuclear magnetic logging,core micro-analysis data and gas testing results,and the causes of resistivity differences and different intrusion characteristics were found out. The results show that fluid property of tight sandstone reservoir is not the dominant factor for the difference of resistivity. The low resistivity is mainly caused by co-conductivity of bound water caused by clay minerals at the edge of pore throat and capillary water in the connectable pore throat. The medium and high resistivity is mainly related to the non-conductivity of isolated pore. The invasion characteristics are mainly related to gas-bearing property and the communication ability of throat. Low resistivity negative difference reservoir is indicator of gas-bearing property and high-quality pore structure. No difference in low resistivity is related to the immovable water conductivity caused by flaky throat,capillary resistance and clay minerals preventing drilling fluid invasion. No difference between medium and high resistivity is related to the inability of conduction and invasion of isolated pore. It is the common influence of sedimentation,diagenesis and later accumulation that leads to the formation of such electrical characteristics. The research results are of great significance for guiding exploration and development of tight reservoirs in the study area.

Quantitative characterization of fault identification using likelihood attribute based on dip-steering filter control

ZHANG Lu, HE Feng, CHEN Xiaozhi, ZHU Yanhe, HAN Gang, LI Qixin

2020, Vol.32(2): 108–114 Abstract ( 318 ) PDF (7417 KB) ( 340 )

doi: https://doi.org/10.12108/yxyqc.20200211

With the development of tight gas exploration,fault plays an important role in controlling the distribution of gas reservoirs and improving the physical properties of reservoirs. Restricted by many factors,such as random noise and seismic footprints,seismic data have low signal-to-noise ratio and poor imaging quality. The clarity of variance or coherence attributes commonly used to identify faults cannot meet the requirements of guiding microfault combination in plane. In order to solve the problem of seismic data interpretation,the method of likelihood attribute controlled by dip-steering filter was used to improve the accuracy of fault identification. Based on the likelihood attribute cube,the threshold of random noise and fault was determined. Combining with regional geological analysis,it is considered that when the value of likelihood attribute is less than 0.3,it is noise,otherwise,it is fault. Finally,fracture density and connectivity can be calculated by using the results of fracture prediction,which can semi-quantitatively or quantitatively describe the development of fracture,and comprehensively understand the distribution of fracture in plane,profile and three-dimensional space. This method breaks through the traditional fault identification method in seismic interpretation, solves the problem that fault and lithofacies changes cannot be distinguished by using conventional coherence method,and improves the accuracy and reliability of seismic interpretation and provides technical support for horizontal well trajectory design and fracturing scheme optimization.

Fracture classification method based on proximal support vector machine

HE Jian, WU Gang, NIE Wenliang, LIU Songming, HUANG Wei

2020, Vol.32(2): 115–121 Abstract ( 247 ) PDF (4051 KB) ( 448 )

doi: https://doi.org/10.12108/yxyqc.20200212

Fractured oil and gas reservoirs are widely found in all kinds of rock formations,how to make fine characterization and comprehensive prediction of fracture zone is the key to the exploration of fractured oil and gas reservoirs. In order to avoid the problem of multiple solutions,many scholars usually use multi-attribute to predict it synthetically. However,there are many complex nonlinear relationships between the development degree of cracks and some seismic attributes,the effective use of the correspondences for nonlinear prediction is also a difficult problem in the comprehensive prediction of fracture zones. The proximal support vector machine algorithm was introduced into the classification of fracture zone,and the nonlinear model between three kinds of seismic properties depicting reservoir fracture zone and crack development information in well were established, and the best discriminating rule reflecting the characteristics of fracture zone was obtained. Based on the rule, multiple seismic attributes can be comprehensively discriminated,the multi-solution of single attribute was overcome,and the classification accuracy of reservoir fracture zone was improved. Example showed that the algorithm weakened the limitation of identifying reservoir fracture zones by single factor classification,and it can provide a new research idea for the accurate classification of the development of fracture zones in rock formations.

Influence of vertical heterogeneity of reservoirs on in-situ CO₂ profile control and flooding effects

ZHENG Yufei, LI Xiang, XU Jingliang, ZHENG Weijie, YU Meng

2020, Vol.32(2): 122–128 Abstract ( 251 ) PDF (2318 KB) ( 445 )

doi: https://doi.org/10.12108/yxyqc.20200213

In order to study the influence of vertical heterogeneity of offshore oil reservoirs on in-situ CO2 profile control and flooding effect,12 groups of inter-layer heterogeneity models and 3 groups of in-layer heterogeneity models were established respectively. The adaptability of in-situ CO2 profile control and flooding to in-layer heterogeneity,interlayer heterogeneity and permeability ratio was investigated by displacement experiments. The results show that under the condition of the same permeability of each layer,the recovery improvement range of insitu CO2 profile control and flooding on the in-layer heterogeneity models can reach 27.40%-31.03%,while that on the inter-layer heterogeneity models was only 17.38%-22.05%,indicating that the CO2 profile control and flooding technology was mainly affected by inter-layer heterogeneity. For inter-layer heterogeneity models with same medium and low permeability layer,the higher the permeability ratio,the better the enhanced oil recovery effect of in-situ CO2 profile control and flooding. Permeability mean value were used to characterize the effect of inter-layer heterogeneity. Enhanced oil recovery of in-situ CO2 profile control and flooding showed a trend of increasing and decreasing with the increase of permeability mean value. Field tests showed that in-situ CO2 profile control and flooding technology had good oil-increasing effect in offshore oilfields and had broad application prospects.

Experiment of minimum miscible pressure of CO₂ flooding in ultra-low permeability reservoir

DAI Bo, WANG Leifei, ZHUANG Jian, YUAN Weibin, WANG Xuesheng

2020, Vol.32(2): 129–133 Abstract ( 351 ) PDF (1780 KB) ( 443 )

doi: https://doi.org/10.12108/yxyqc.20200214

When measuring the minimum miscibility pressure (MMP) of CO2-crude in ultra-low permeability reservoirs,the conventional method has the problems of long measurement period and large workload,and the miscible state of CO2 and crude oil cannot be directly observed. To determine the MMP of CO2-crude oil in Xinghe ultra-low permeability reservoir quickly and accurately,the interfacial tension(IFT) method was used to conduct indoor experiments on CO2 and crude oil in Xinghe reservoir. The results show that with the increase of equilibrium pressure,the amount of CO2 dissolved in crude oil increases,and the IFT between CO2 and crude oil can be divided into two stages,and both decrease linearly. When the equilibrium pressure increases from 4 MPa to 28 MPa,the IFT between CO2 and crude oil decreases from 17.72 mN/m to 1.56 mN/m. The MMP of Xinghe reservoir measured by IFT method is 22.5 MPa,which is slightly higher than that of 22.3 MPa measured by thin tube experiment. The difference between the two values is only 0.9%,indicating that the IFT method has good accuracy in measuring the MMP of ultra-low permeability reservoir. Through the above research,the MMP of Xinghe reservoir was determined,which provides theoretical support for the development of the CO2 stimulation production plan for the Xin he reservoir. However,since the MMP is higher than the current reservoir pressure of 17.5 MPa, CO2 and crude oil can't achieve miscibility under current reservoir conditions.

Productivity forecast based on support vector machine optimized by grey wolf optimizer

SONG Xuanyi, LIU Yuetian, MA Jing, WANG Junqiang, KONG Xiangming, REN Xingnan

2020, Vol.32(2): 134–140 Abstract ( 473 ) PDF (1709 KB) ( 722 )

doi: https://doi.org/10.12108/yxyqc.20200215

Conventional linear regression and empirical formulas for predicting initial productivity have limited application scope and large prediction error, and are difficult to characterize the nonlinear variation of initial production under the influence of multiple factors. Therefore,machine learning algorithm was introduced to improve the accuracy of the prediction. Taking an ultra-low permeability oilfield as an example, ten factors affecting the initial productivity were selected from three aspects of geology, development,and engineering,and the linear correlation among these factors was analyzed by Pearson correlation. Random Forests was applied to identify the main controlling factors of initial productivity. Support vector machine(SVM)optimized by grey wolf optimizer(GWO)was used to establish the prediction model of initial productivity of oil well for the first time. The results show that the main controlling factors of initial productivity in ultra-low permeability oilfields are sand volume of the fracturing,perforation thickness, initial water saturation, effective oil layer thickness and sand intensity of fracturing. The GWO-SVM model has faster operation speed and higher accuracy compared with multivaluable linear regression and SVM optimized by grid searching. The research results can provide reference for the initial productivity evaluation of oil wells.

Three-dimensional water flooding physical simulation experiment of horizontal well in heavy oil reservoir with strong bottom water

DU Xulin, DAI Zong, XIN Jing, LI Hailong, CAO Renyi, LUO Donghong

2020, Vol.32(2): 141–148 Abstract ( 346 ) PDF (4834 KB) ( 355 )

doi: https://doi.org/10.12108/yxyqc.20200216

The marine sandstone heavy oil reservoirs in the Pearl River Mouth Basin in the South China Sea are characterized by strong energy of bottom water,non-uniformed distribution of interlayers,and difficult development. Conventional experimental standards barely reveal reservoir sweep feature under high-intensity water flooding. A three-dimensional water flooding physical simulation experiment of horizontal well was designed based on the characteristics of the heavy oil reservoir named X in Pearl River Mouth Basin. The oil viscosity and interlayer distribution range were proposed as the main controlling factors affecting water flooding effect, and the characteristics of water cresting and sweep feature in water flooding development of heavy oil reservoirs with strong bottom water were analyzed. The results show that the changing process of water cresting in heavy oil reservoir is local coning-local water breakthrough-local upper support-expansion around water breakthrough point. There exists obvious oil-water transitional zone in heavy oil reservoir water flooding, and the sweep region is limited in the late stage of development, so large displacement measures can be used. The remaining oil in the oil-water transitional zone of flood sweep zone is a potential tapping target. The problem of heterogeneity along horizontal wells should be focused on the development of heavy oil reservoirs water flooding. For heavy oil reservoirs with interlayer, there is a small amount of residual oil at the bottom of the small range interlayer. Since the secondary edge water is easily formed when the bottom water flows around the large interlayer so that the sweep region along the wellbore direction increases greatly, and there is a large amount of residual oil at the bottom of the interlayer called "eaves oil". This study can provide research direction for waterproofing and tapping potential of remaining oil of heavy oil reservoirs with strong bottom water.

Mechanism of nitrogen flooding in Yong 66 block of Yong'an Oilfield,Bohai Bay Basin

GUAN Hua, GUO Ping, ZHAO Chunlan, TAN Baoguo, XU Dongmei

2020, Vol.32(2): 149–160 Abstract ( 325 ) PDF (6011 KB) ( 366 )

doi: https://doi.org/10.12108/yxyqc.20200217

In order to study the mechanism of nitrogen flooding and its variation law in Yong 66 block of Yong'an Oilfield in Bohai Bay Basin,fluid phase experiments and numerical simulations were carried out on the basis of geological study. The results show that:(1)During the nitrogen injection process,the formation dip angle,displacement velocity and capillary pressure have obvious effects on the change of oil saturation and interfacial tension. (2)The greater the formation dip angle and displacement velocity are,more crude oil is displaced to the bottom of the reservoir,the greater the oil saturation at the bottom of the reservoir is. At the same time,the upper fluid of the reservoir becomes the two phases of oil and gas,and the interfacial tension increases.(3)During the process of nitrogen flooding,as the capillary pressure increases,the resistance of the gas entering into the pores increases, and so does the oil saturation at the bottom,although the accumulation of crude oil to the bottom of the reservoir slows down. Also,the tension at the top interface increases,while the range and degree of the change gradually decreases. The research results have a guiding role in the application of nitrogen flooding to enhance oil recovery in the development of oil and gas fields.

Fracturing effect evaluation based on borehole microseismic monitoring method: a case study from well Y22 in Jilin exploration area

ZHAO Chaofeng, JIA Zhenjia, TIAN Jiantao, GAO Rongjin, ZHANG Wei, ZHAO Jianyu

2020, Vol.32(2): 161–168 Abstract ( 306 ) PDF (4561 KB) ( 382 )

doi: https://doi.org/10.12108/yxyqc.20200218

Evaluation of reservoir hydraulic fracturing effect is of great significance for guiding the fine development of oil and gas fields. In order to accurately evaluate the fracturing effect,a fracturing effect evaluation method of microseismic monitoring in wells was proposed. On the basis of accurately locating microseismic events,the temporal and spatial distribution characteristics of microseismic events were analyzed,ineffective microseismic events were eliminated,the length,width,height,trend,reconstruction volume of fracture network were quantitatively described by using effective events,and fracturing effect was objectively evaluated by explaining the causes of fractures in combination with reservoir properties and fracturing operation parameters. The application results of well Y22 in Jilin exploration area show that the fracturing fracture strike is consistent with that of surrounding small faults or natural fissures. The results of log interpretation and microseismic monitoring are correlated,and the fractured reservoir with better log interpretation has relatively greater fracturing volume,more microseismic events and higher fracture complexity. The discrete microseismic events during fracturing are irrelevant to the fracture channeling layer but result from stress release in the low stress area that caused by pressure transmission. The formation energy deficit of other wells around well Y22 caused by primary fracturing and later production of oil and gas results in the asymmetry of the fracturing fractures in well Y22. The research results can be used to explain the temporal and spatial distribution characteristics of microseismic events,improve the understanding of fracturing and reservoir properties, and evaluate the fracturing effect objectively and accurately.

Extending regularity of fracture height by acid fracturing in carbonate reservoir: a case study of Qixia Formation in western Sichuan

LUO Zhifeng, HUANG Jingyun, HE Tianshu, HAN Mingzhe, ZHANG Jintao

2020, Vol.32(2): 169–176 Abstract ( 210 ) PDF (8230 KB) ( 284 )

doi: https://doi.org/10.12108/yxyqc.20200219

Acid fracturing is a very effective means of increasing production for the development of deep marine carbonates in western Sichuan. Currently, there exists many problems in the development of deep marine carbonates in western Sichuan such as strong heterogeneity, thin reservoirs, and small differences of reservoir stress. Technically, the main problem in transformation is the control of fracture height. Therefore, the influence of engineering geological factors on fracture height was studied with the geological conditions of the X gas well in western Sichuan into consideration by means of finite element numerical simulation. Moreover, this simulated model was verified by the results of the fracture height obtained by net pressure fitting on FracPT software, microearthquake data and data of production well temperature. For last analysis, the results of this paper show that the viscosity of the working fluid, the construction displacement and the injection scale, and the difference increase in inter-stress of the reservoir barrier are good for controlling the fracture height. The result well guides the parameter optimization of the X gas well construction. After the construction, the daily gas production of the X gas well test is 104, 500 m3. This paper plays a guiding role in the optimal design of acid fracturing and on-site construction in deep marine carbonate rocks in western Sichuan.