Lithologic Reservoirs

In order to understand the characteristics of Paleogene oil shale reservoirs in Yingxi area of Qaidam Basin, the petrological characteristics,physical properties,reservoir space,oil-bearing properties and source-reservoir occurrence relationship were analyzed,and favorable reservoir development areas were optimized. The results show that:(1)mineral compositions of reservoir-rocks in the upper member of Xiaganchaigou Formation demonstrate typically mixed features,including carbonates,terrigenous clastic,argillaceous and evaporite minerals. (2)According to the comprehensive geological and logging responses characteristics,the reservoirs in the study area were divided into three types, including laminated shale/argillaceous carbonate reservoirs, massive shale/argillaceous carbonate reservoirs and phenocrystal shale/argillaceous carbonate reservoirs.(3)The main pore spaces in reservoirs include inter-crystal pores,intergranular/inter-crystal dissolved pores,inter-breccia pores and fractures. In summary,the physical properties of reservoirs are nor good,their porosities range from 4% to 6% and permeabilities range from 0.05 to 0.10 mD.(4)The reservoir is characterized by "intra-source accumulation and wholebody oil-bearing",and the oil-bearing abundance of the target layer is controlled by reservoir properties and its relationship with the source rocks. This study results have a guiding role for shale oil exploration in Yingxi area.

Sedimentary characteristics of Lower Cambrian Canglangpu Formation in Gaoshiti-Moxi area,Sichuan Basin

PENG Jun, CHU Jiangtian, CHEN Youlian, WEN Jian, LI Yading, DENG Sisi

2020, Vol.32(4): 12–22 Abstract ( 311 ) PDF (5643 KB) ( 430 )

doi: https://doi.org/10.12108/yxyqc.20200402

In recent years,the discovery of the extra-large integral marine carbonate gas field in Gaoshiti-Moxi area in central Sichuan province has revealed that the Lower Cambrian has great potential for oil and gas exploration and development. Unlike Longwangmiao Formation which is of the main target in this area, the study on petroleum geological basis of Canglangpu Formation is still rather weak,especially on the subject of sedimentary facies. Therefore,it is quite essential to do study on the sedimentary characteristics of Canglangpu Formation in this area. Based on theories of sequence stratigraphy,sedimentology and logging geology,the sedimentary characteristics of Canglangpu Formation in Gaoshiti-Moxi area were studied by combining the data of coring,drilling,logging and core cuttings analysis as well. The results show that the lithology in Canglangpu Formation shows the change law of clastic rock-carbonate rock-clastic rock-carbonate assemblage from bottom to top. There are three sedimentary models developed in Canglangpu Formation,including detrital shore-shelf,carbonate gentle slope and storm deposit,two types of sedimentary facies,including shelf and inner gentle slope,and five types of sedimentary subfacies,including mixed shallow water shelf,shallow water shelf,mixed tidal flat,lagoon and shoal. There is mainly continental shelf facies in Canglangpu Formation,and there presents the sedimentary subfacies succession law of shallow water shelf-mixed shallow water shelf-shallow beach-mixed tidal flat-shallow water shelf-mixed shallow water shelf-mixed tidal flat. The research results may provide a reference for the further study on Lower Paleozoic petroleum geology and distribution and prediction of high-quality reservoirs in GaoshitiMoxi area.

Structural characteristics and its impacts on hydrocarbon accumulation in Zaysan Basin,Kazakhstan

ZHU Zhenjun, HUANG Guangming, QIU Jin, LIU Kangning, LI Qi, HU Junjie

2020, Vol.32(4): 23–35 Abstract ( 387 ) PDF (10617 KB) ( 733 )

doi: https://doi.org/10.12108/yxyqc.20200403

The Zaysan Basin in Kazakhstan is one of the important petroliferous basins in Central Asia. Due to the complex structure,the oil and gas enrichment law is unclear,which limits the exploration and development process in some degree. Based on the fine three-dimensional seismic interpretation,combined with the studies of tectonic evolution,hydrocarbon generation processes,and reservoir conditions, and through the analysis of the comparison between tectonic activity intensity and oil and gas exploration results at different periods in different areas of the basin,the structural characteristics and oil and gas accumulation model in Zaysan Basin were systematically studied. The results show that Zaysan Basin has experienced four-stage subsidence and four-stage extrusion reversal since the Permian. At present,the basin morphology is dominated by extruded structures,and various tectonic styles such as imbricate structure,ramp structure and pop up structure are developed. The thrust faults activity at the end of the Jurassic period controlled the rudiment structural framework of the main area,the northeast area and the K-zone,and the present tectonic form shaped by the re-compression and thrust of faults at the Late Pliocene. The Zaysan Basin can be roughly divided into three large reservoir-forming periods. The deep oil and gas reservoirs are self-generating and self-storing stratigraphic and lithologic reservoirs,and the distribution of shallow gas reservoirs is mainly controlled by the distribution scale of deep reservoirs and the favorable traps such as shallow thrust anticlines and broken anticlines formed during the Himalayan period. The Indosinian tectonic movement played a very important role in controlling the hydrocarbon accumulation in Zaysan Basin. The S well area,the K-zone and the M-well area,where the Indosinian activity was strong(referring to the severe erosion of the Triassic strata or the thrusting activity is strong),the traps are generally empty. The drilling test oil is basically out of water, and the oil and gas reservoirs that have been confirmed are in areas with weaker activities. Based on the above research,the northern and southern margin of the eastern part of the basin should be favorable areas for the future search of oil and gas reservoirs in Zaysan Basin.

Characteristics of fractured bedrock gas reservoir in Jianbei gas field,Qaidam Basin

CHEN Gengxin, WANG Jiangong, DU Binshan, LIU Yingru, LI Yanli, YANG Huijie, LI Zhiming, YU Xiaofeng

2020, Vol.32(4): 36–47 Abstract ( 216 ) PDF (14733 KB) ( 516 )

doi: https://doi.org/10.12108/yxyqc.20200404

In order to clarify the bedrock reservoir characteristics of Jianding Mountain area in front of Altun Mountain in Qaidam Basin, the petrology,mineralogy,reservoir space type,fracture development characteristics and gas-bearing controlling factors were systematically studied by using core data,rock section,mercury injection curve,industrial CT,scanning electron microscopy and logging data. The results show that:(1)The bedrock in Jianbei area is mainly composed of massive variegated quartz diorite and granodiorite, and the reservoir spaces include weathering leaching dissolved pore,matrix micropore,fracture and dissolved pore in fracture.(2)Bedrock fractures can be divided into two types,one is structural fracture with 2-stage genesis,the other is diagenetic cleavage fracture, both of which are controlled by basement fracture. The reservoir spaces of the weathering and leaching zone of bedrock include dissolved pores and fractures formed by weathering and leaching. Both macropore throat and micro-pore throat are well developed,but the micro-pore throat is main. The connection pore diameter is mostly 1-5 μm. The distance from the top of bedrock determines the quality of reservoir. The reservoir spaces of fracture dissolution zone include fractures and dissolved pores in fracture. The structural activity in geological history period controls the reservoir quality. The research results can be used for reference in oil and gas exploration of weathered crust of bedrock.

Influence of paleogeomorphic characteristics on sedimentary system and hydrocarbon distribution in Tanan Depression

SUI Liwei

2020, Vol.32(4): 48–58 Abstract ( 282 ) PDF (8715 KB) ( 264 )

doi: https://doi.org/10.12108/yxyqc.20200405

In order to research the hydrocarbon distribution of Tongbomiao Formation and Nantun Formation in Tanan Depression of Hailar-Tamuchage Basin,three-dimensional seismic,logging and mud logging data were used to restore the paleogeomorphology through basin structural modeling,so as to clarify the control effect of paleogeomorphology on sedimentary system and hydrocarbon distribution in different geological periods. The results show that:(1)The sedimentary period of the Tongbomiao Formation has the characteristics of "extensive troughs and multi-sources sediment",and the source is mainly the fan delta in NW-SE and paleo uplift in WS. During the sedimentary period of Nantun Formation,there were four large-scale subsidence centers developed in the whole area,and the subsidence center gradually migrated from the west sub-depression to the depression center. (2)Alluvial fan,fan delta and coastal shallow-lake facies were mainly developed in Tongbomiao Formation, and the formation and distribution of alluvial fan were controlled by the paleo uplift in the depression. Delta,fan delta,nearshore subaqueous fan,sublacustrine fan and lacustrine were mainly developed in Nantun Formation, and paleo-uplift and paleo-depression controlled the formation of nearshore underwater fan and the distribution of hydrocarbon source rocks respectively.(3)The paleogeomorphology of Tanan Depression controlled the distribution of oil and gas in the form of "paleo-uplift and slope controlled reservoir,paleo-depression controlled source,paleofault and slope controlled accumulation". In the west,there were structural reservoirs controlled by "source-reservoir connection" and "paleo-fault and slope" combination,while in the east,there were lithologic reservoirs controlled by steep slope with nearshore subaqueous fan and sublacustrine fan as reservoirs. Paleogeomorphic evolution as a decisive role in the distribution of source and reservoir,and the "paleo-fault and slope" combination as a decisive role in the transportation and accumulation of hydrocarbon. The research results have important guiding significance for understanding the law of hydrocarbon distribution in Tanan Depression.

Sedimentary characteristics of fan delta during initial rifting stage in Sujiatun sub-depression,Songliao Basin

YANG Wenjie, HU Mingyi, SUYA Latu, LIU Chang, YUAN Yi, LI Jinchi

2020, Vol.32(4): 59–68 Abstract ( 287 ) PDF (9377 KB) ( 328 )

doi: https://doi.org/10.12108/yxyqc.20200406

As a kind of good oil and gas reservoir,sandy conglomerate bodies of fan delta have been paid more attention. In order to deepen the understanding of the sedimentary characteristics of the fan delta during the initial rifting stage in the fault basin,taking Huoshiling Formation in Sujiatun sub-depression of Songliao Basin as an example,the development rules,sedimentary characteristics and controlling factors of fan delta in the initial rifting stage were studied by using core,well logging,three-dimensional seismic data and paleogeomorphic restoring technology. The fan delta sedimentary model in the initial rifting stage of the faulted lacustrine basin was established. The results show that:(1)During the initial rifting stage of Sujiatun sub-depression,there was a grabentype faulted lake basin with EW double faults developed,the terrain height difference was large within the area, the tectonic movement was active,and the sediment source were mainly from the northwest,southwest and east of the sub-depression.(2)During the formation stage of Huoshiling Formation,fan delta sedimentary system was widely developed. The lithology was dominated by thick bedded variegated and gray sandy conglomerate with thin bedded gray mudstone. The logging curves were mostly box or bell shaped with high amplitude. The fan delta deposits are characterized by oblique progradation reflection,wedge-shaped or mound shaped disordered reflection structure on the seismic section.(3)The distribution of the sedimentary system was mainly controlled by basin faults and paleogeomorphology,forming the sedimentary pattern of "lacustrine facies across the central sag,fan delta facies in the east-west fault terrace" and the source reservoir assemblage of "hydrocarbon generation in the center and reservoirs on both sides".(4)The structural activity in the initial rifting stage is the main controlling factor for the development of fan delta system. The basin-controlling fault not only controls the distribution of sedimentary facies belt and reservoir sand bodies,but also continuously affects the sedimentary filling evolution trend of faulted lacustrine basins. The research results could provide a geological basis for oil and gas exploration in deep strata of fault depression of continental basin.

Sedimentary characteristics and models of shallow water delta front of the lower first member of Shahejie Formation in Gaoyang area,Lixian Slope

XUE Hui, HAN Chunyuan, XIAO Boya, WANG Fang, LI Ling

2020, Vol.32(4): 69–80 Abstract ( 264 ) PDF (7572 KB) ( 237 )

doi: https://doi.org/10.12108/yxyqc.20200407

The lower first member of Shahejie Formation(Es1X)in Gaoyang area,Lixian Slope,which contain sizable hydrocarbon resources,was the main oil layers in recent years. In order to make clear the distribution characteristics of sedimentary facies and define the direction of the further exploration and development,cores, well logging and seismic data were used to study the sedimentary facies symbols,types,distribution and models. The results show that:(1)Shallow water delta front widely developed in Es1X in Gaoyang area of Lixian Slope, the sand bodies were mainly composed of fine sandstone,siltstone and mudstone,and nine lithofacies types can be identified.(2)The logging facies in the study area can be divided into five types,including box-shaped,bellshaped,finger-shaped,funnel-shaped and flat-shaped.(3)On the seismic profiles,the Es1X shows small scale imbricated progradation reflection and sub-clinoformal seismic reflection.(4)The shallow water delta front in Gaoyang area mainly developed four kinds of sedimentary microfacies,which are underwater distributary channel, mouth bar,sheet sand,underwater diversion bay. The sedimentary microfacies features and evolution law of Es1X are closely related with the lake-level fluctuation,and the distribution and evolution of sedimentary microfacies at different period are different. According to the sedimentary characteristics above,the development models of shallow-water delta front of lacustrine basin in atrophy period and spreading period were established,which can provide geological basis for hydrocarbon exploration in similar areas.

Geochemical characteristics and genesis of heavy oil in Beibuwan Basin

JIN Qiuyue, YANG Xibing, HU Lin, LU Mei

2020, Vol.32(4): 81–88 Abstract ( 241 ) PDF (3510 KB) ( 267 )

doi: https://doi.org/10.12108/yxyqc.20200408

Several heavy oil fields have been found in Weixinan Sag and Wushi Sag of Beibuwan Basin. In order to study the characteristics and genesis of heavy oil,the physical properties, components, saturated hydrocarbon characteristics, biomarkers, oil and gas source and basin simulation analysis were carried out. The results show that:(1)The heavy oil in Beibuwan Basin is mainly distributed in uplift, slope zone and near depression zone, with high density and high viscosity.(2)There are three types of heavy oil in Beibuwan Basin. The first type is the crude oil generated by the source rocks in the lower part of the second member of Liushagang Formation in the center of the sag and transported to the trap for reservoir formation.Due to later uplift and denudation, the burial depth is less than 2 000 m. The thin overburden causes the reservoir to be biodegraded. This kind of crude oil has high maturity and high content of c30-4-methylsterane. The components were destroyed to different degrees and the saturated hydrocarbon and aromatic hydrocarbon components were lost in order. The second type of heavy oil is mainly distributed in the near-depression zone, which is the crude oil generated from the local lowthermal evolution oil shale and shale. It is characterized by low maturity, low Ts/Tm value and low contentof C30-4-methylsterane. The reservoir is accumulated in the near depression and buried in the near hydrocarbon generation threshold,and it is the early primary heavy oil. The third type ofheavy oil is mainly distributed in the slope belt, it is mainly composed of the mature crude oil generated from the lower source rock of the second member of Liushagang Formation in the deep depression and the low mature heavy oil generated from the upper source rock in the local area. Meanwhile,influenced by migration, diffusion, adsorption and other factors,the crude oil thickens. The content of C30-4-methylsterane is medium,and the buried depth of reservoir is more than 3 000 m. The mixed heavy oil is not biodegraded. The research results are of great significance for optimizing exploration and development deployment and guiding oil exploration in Beibuwan Basin.

EXPLORATION TECHNOLOGY

Controlling factors and prediction methods of multiples of Dengying Formation in Gaoshiti-Moxi area,Sichuan Basin

DAI Xiaofeng, XIE Zhan'an, DU Benqiang, ZHANG Ming, TANG Tingke, LI Jun, MOU Chuan

2020, Vol.32(4): 89–97 Abstract ( 275 ) PDF (7826 KB) ( 298 )

doi: https://doi.org/10.12108/yxyqc.20200409

There are multiples interferences of Dengying Formation in Gaoshiti-Moxi area,which reduces the accuracy of seismic reservoir prediction. It is necessary to identify and predict multiples in seismic data, so as to reduce the influence of multiples interference on current well location deployment. In view of the shortcomings of the existing methods of multiples recognition and prediction,the multiples were identified by velocity spread of the energy clusters on the seismic velocity spectrum. The multiples prediction of Dengying Formation was realized in Gaoshiti-Moxi area. The result was consistent with drilled well data,which proves the effectiveness of the method. According to the comprehensive analysis,the multiples of Dengying Formation are strong in the south and weak in the north on the whole,and have strong horizontal heterogeneity. Through seismic forward modeling and comprehensive analysis of seismic data,the areas with residual Ordovician strata develop more multiples,and multiples interference is stronger in the syncline area. According to the degree of multiples interference,the 3D seismic data in Gaoshiti-Moxi area can be divided into three types. Type Ⅰ multiples interference is weak,and seismic amplitude can truly reflect impedance characteristics of the strata. Type Ⅱ multiples' energy is similar to primary wave,and seismic data has more multiple solution. Type Ⅲ multiples interference is strong,and seismic data cannot represent the characteristics of strata. Based on the multiples prediction results,geologists can judge the reliability of seismic interpretation results,reasonably avoid risks,reduce the influence of multiples interference,and reduce the risk of well location deployment.

Identification of complex carbonate lithology by logging based on XGBoost algorithm

SUN Yushu, HUANG Yun, LIANG Ting, JI Hancheng, XIANG Pengfei, XU Xinrong

2020, Vol.32(4): 98–106 Abstract ( 410 ) PDF (7081 KB) ( 565 )

doi: https://doi.org/10.12108/yxyqc.20200410

Carbonate reservoirs are affected by a variety of factors during the formation process,and the reservoir lithology is complex and diverse. Logging data are of great significance for carbonate lithology identification. In order to solve the problem that the traditional logging lithology identification method and traditional machine learning have low recognition accuracy for complex carbonate lithology,taking the Ordovician carbonate rocks in the northern Langgu Depression as an example, based on log data, XGBoost algorithm was appied to lithology identification of complex carbonate rocks,and the performance of the model was comparied with the decision tree C4.5 algorithm and the support vector machine algorithm. The results show that the lithology identification model based on XGBoost algorithm has an accuracy rate of 88.18% for the identification of carbonate lithology in the study area. Compared with decision tree C4.5 and support vector machine,the accuracy rate is increased by about 10%. And the XGBoost algorithm uses multi-threaded and distributed computing methods,the training time is greatly shortened. It shows that the lithology identification model established by XGBoost algorithm can effectively identify complex carbonate lithology and provide a new idea for logging identification of complex carbonate lithology.

Mineral component inversion of complex lithologic reservoirs in Bozhong 19-6 Archean buried hill

ZHU Boyuan, ZHANG Chaomo, ZHANG Zhansong, ZHU Linqi, ZHOU Xueqing

2020, Vol.32(4): 107–114 Abstract ( 295 ) PDF (3711 KB) ( 418 )

doi: https://doi.org/10.12108/yxyqc.20200411

Lithology of Bozhong 19-6 buried hill structural belt is very complicated.As a result,it is difficult to accurately calculate the porosity parameters directly from the log curve. The data of logging and experimental cores were used to analyze the lithology of buried hill reservoirs of Archean from the aspects of alteration, logging response characteristics,porosity,mineral content and fractures. A heavy mineral identification model was established and double indicator curves were used to identify heavy minerals. A set of mineral composition inversion models suitable for the complex lithologic reservoirs of buried hills of Archean in Bozhong19-6 was established. The results show that the metamorphic rocks,igneous rocks,and other rocks in the study area are complex in lithology,making it difficult to calculate accurate log curves for rock skeletons. The mass fraction of heavy minerals in buried hill formations is about 8%, and pyrite,siderite and iron dolomite are common. The effective porosity calculated by this inversion model agrees well with the core. The improved multi-mineral component inversion method can reduce the impact of complex mineral component on the physical properties of Bozhong 19-6 buried hill formation. The inversion mineral component and porosity are basically consistent with the experimental analysis. This study can provide some technical support for exploration and development in the area.

OIL AND GAS FIELD DEVELOPMENT

Evaluation and development countermeasures of undeveloped reserves in Sulige tight sandstone gas reservoir

HOU Kefeng, LI Jinbu, ZHANG Ji, WANG Long, TIAN Min

2020, Vol.32(4): 115–125 Abstract ( 330 ) PDF (3336 KB) ( 539 )

doi: https://doi.org/10.12108/yxyqc.20200412

In order to implement the proved reserves and remaining undeveloped reserves of strong heterogeneous tight sandstone gas reservoirs in Sulige gas field and evaluate the potential of steady production, based on geological knowledge database,the reservoir was divided into several calculation units both in plane and in vertical,and the reserves of the units was also recalculated separately with volumetric method. Reserves classification and evaluation criteria were established based on reservoir static parameters,gas well production index and internal rate of return. According to the evaluation criteria,the reserves can be divided into three types:enriched area,dense area and water-rich area. And the used and remaining unused reserves were evaluated by the "single well controlled area method". The evaluation results show that there is a great difference in the degree of developed reserves among different blocks in Sulige gas field,overall the comprehensive utilization degree of reserves is 40.1%. The remaining undeveloped reserves are large in scale and have good potential for stable production. Under the current economic and technological conditions,improving reserves utilization in enriched and dense areas by through well pattern infilling,sidetracking horizontal wells and re-perforation modification of gas well are main realistic ways to stable production of gas field. Effective utilization of remaining reserves in water-rich areas still needs to be tackled further.

New method of recognizing architecture interfaces of complex meander belt deposition and its application

HE Kang, ZHANG Pengzhi, ZHOU Junliang, GAN Liqin, SHU Xiao

2020, Vol.32(4): 126–135 Abstract ( 245 ) PDF (14392 KB) ( 253 )

doi: https://doi.org/10.12108/yxyqc.20200413

In order to propose effective stimulation measures,it is necessary to find a new method to depict the sand reservoir structure of complex meander belt and study the geological factors of uneven efficiency of horizontal water injection in production well group in offshore oilfield. This paper took the oil-bearing sand body NmⅢ2 of Q oilfield in Bohai for example to introduce a new reservoir architecture method. First,nine different cutting relations between every two rivers were concluded by classical meandering stream and the result of micro-facies correlation among the wells. Through combined seismic record obtained from seismic forward modeling,we found that different cutting relations make different seismic wave features. Second,the different intensity of cutting results in the different strength of seismic response. So,we tried to use a single amplitude attribute and dual seismic attribute fusion technology to locate all these different cutting relations accurately. Last,on the basis of the works above, combined with the restoring ancient landscape,the prediction of sand body thickness and configurational formula, precise recognition of architecture interfaces of complex meander belt deposition would be realized. The results show that the meander belt sand bodies were divided into several different connective or semi-connective bodies by the architecture interfaces. It is recognized that the permeability of the different cutting relations is different. The research results can provide reliable geologic accordance for optimizing injection-production structure.

Influence mechanism of acidification on oil recovery during CO₂ flooding

SUN Huizhu, ZHU Yushuang, WEI Yong, GAO Yuan

2020, Vol.32(4): 136–142 Abstract ( 313 ) PDF (2326 KB) ( 396 )

doi: https://doi.org/10.12108/yxyqc.20200414

The acidification of CO2 can cause damage to the reservoir to a certain extent. In order to reveal the influence mechanism of acidification on oil recovery,six core samples with the same level of permeability were selected for CO2 flooding tests under the conditions of reservoir temperature and pressure,and then the influence mechanism of acidification on oil recovery was evaluated by NMR technique. The results show that the pH value of the displaced fluids is lower than that of the original formation water,and the change of the ion concentration before and after CO2 flooding reflects the dissolution of feldspar and carbonate minerals. The permeability of the core samples decreased after CO2 flooding,and the longer the reaction time,the greater the decrease of permeability. The ultimate recovery factor of the core sample is inversely proportional to the reaction time. The core sample with a reaction time of 240 h was reduced by 27.31% compared to the core sample of 0 h. Comprehensive analysis shows that the long-term acidification and corrosion reaction products of CO2 flooding and the exfoliated clay particles will block the pore throat,resulting in the decline of reservoir seepage capacity, which in turn affects the displacement efficiency and ultimate recovery factor of CO2 flooding.

Influence of estuary bar structure on reservoir exploitation of upper Sha-1 submember in Dawangzhuang area,Raoyang Sag

LYU Wenrui, ZHANG Feng, JI Youliang, ZHOU Yong, LUO Nina, ZHANG Yilou, LIANG Xingru, CHENG Yuzong

2020, Vol.32(4): 143–154 Abstract ( 184 ) PDF (8407 KB) ( 196 )

doi: https://doi.org/10.12108/yxyqc.20200415

Underwater distributary channels and estuary bar sandbodies were developed in the third and fourth oil members of the upper Sha 1 member(Es1)in Dawangzhuang area of Raoyang Sag,and their internal structure influences the development of reservoirs. However, there is a lack of systematic research on the internal structure of estuary bar and the distribution of interbeds in this area. Based on the identification and analysis of sedimentary microfacies,the structural characteristics and reservoir characteristics of estuary bars and muddy interbeds were dissected by using core data,logging and production data. The influence of the internal structure of estuary bars on reservoir development was clarified and the reservoir model was established. The results show that in the third and fourth oil groups of upper Es1 in Dawangzhuang area,delta front subfacies was developed,including three microfacies:underwater distributary channel,estuary bar and underwater distributary bay. Muddy interbeds were developed between and within estuary bars. Along the source direction,estuary bar was S-shaped superimposed pre-accumulation,while in the vertical source direction,the multi-stage estuary bar was stacked vertically. The muddy barriers were developed between the estuary bars,and muddy interbeds were developed within the single estuary bar. There are three types of reservoirs developed in the study area:fault-controlled reservoir, lithology-controlled reservoir and fault-lithology composite reservoir. The muddy barriers between estuary bars in different stages are the reason for the inconsistency of oil-water interface, while the muddy interbeds within estuary bars are thin and the scale is small, which does not affect the connectivity.

Influence of imbibition on the development of fractured low permeability conglomerate reservoir: a case stuey from Urho Formation in Mahu oilfield

CAO Xusheng, HAN Yun, ZHANG Jizhuo, LUO Zhiwei

2020, Vol.32(4): 155–162 Abstract ( 241 ) PDF (2570 KB) ( 530 )

doi: https://doi.org/10.12108/yxyqc.20200416

The development of low permeability conglomerate reservoir in Mahu oilfield is strongly dependent on fractures,and the imbibition between fractures and matrix has an important influence on its development,but the relevant research is very weak at present. The characteristics of imbibition effect of conglomerate of Urho Formation in Mahu oilfield were studied by means of NMR technology,and the imbibition law between fracture and matrix was quantitatively characterized. Furthermore,the influence of imbibition effect on horizontal well development of low permeability conglomerate reservoir in Mahu oilfield was studied by taking the characterization equation into account in the dual-porosity and dual-permeability model. The results show that the conglomerate core from Urho Formation is mainly composed of medium and small pores(T2 T2 T2 < 100 ms) is 37.11%,and its imbibition law is in good agreement with the improved MA index transport model. According to the experimental results based on the dual-porosity and dual-permeability model, after five years of horizontal well development,the fracture recovery was reduced by 24.3%,the matrix recovery was increased by 4.6%,and average recovery was increased by 2.0%. This study is of guiding significance for formulating scientific measures of EOR in the later stage.

PETROLEUM ENGINEERING

Solution and realization of coupled model of temperature and pressure field in deep water gas well testing

LI Zihan, HE Yufa, ZHANG Binhai, ZHONG Haiquan

2020, Vol.32(4): 163–171 Abstract ( 248 ) PDF (3791 KB) ( 453 )

doi: https://doi.org/10.12108/yxyqc.20200417

To seek the solution of the coupled model of temperature and pressure field in deep-water gas well testing,it is necessary to optimize the gas-liquid two-phase flow model. Based on two-phase nozzle flow model,twophase liquid holdup formula and two-phase productivity equation,the differential equations of unsteady pressure drop and heat transfer model about time and space were established,and Newton Raphson method was applied to realize the simulation of the transient process of blowout. The results show that:(1)The method can truly simulate the two stages of liquid level rising and formation gas production in blowout stage. (2)The predicted wellhead parameters are consistent with actual conditions,and the average error of wellhead pressure and temperature is less than 5%,which meets the engineering accuracy requirements.(3)The simulation results reconstructed the dynamic process of induced flow and test completion fluid blowout in wellbore, and can provide basis for reasonable test design.(4)For deep water gas wells with high productivity,larger size string and nozzle should be used to improve well cleaning speed and prevent ice blockage. The example analysis shows that the mathematical model truly reflects the test blowout process of deep water gas wells. The research results have certain guiding significance for the test scheme design and follow-up evaluation of deep water gas wells.

Pressure transient analysis of hydraulic fractured vertical wells with variable conductivity for CO₂ flooding

CUI Yongzheng, JIANG Ruizhong, GAO Yihua, QIAO Xin, WANG Qiong

2020, Vol.32(4): 172–180 Abstract ( 219 ) PDF (2394 KB) ( 598 )

doi: https://doi.org/10.12108/yxyqc.20200418

At present,CO2 flooding with hydraulic fractured vertical wells has become one of the main technologies for the development of low permeability reservoirs. Hydraulic fracture conductivity is a key factor influencing the production performance of fractured wells,and now most well test models were based on the assumption of a constant fracture width,failing to simulate the space variable width of hydraulic fractures. Based on three-zone composite theory,a CO2 flooding well test model of hydraulic fractured vertical wells considering with variable conductivity was established, and the Laplace transformation was adopted to solve this model, and then the numerical inversion was carried out to draw typical well test curve. According to the pressure response characteristics, the pressure transient type curve was divided into nine stages including wellbore storage stage,skin effect stage, bilinear flow stage,linear flow stage,the first radial flow stage,the first transition stage,the second radial flow stage,the second transition stage and the late radial flow. Sensitivity analysis was carried out to investigate the influence of several factors on pressure transient. The results show that the larger the fracture conductivity was,the smaller the pressure of the bilinear flow stage was,and the easier CO2 can be injected. When the space variable conductivity was considered,the pressure of early flow stages increased,and the pressure and pressure derivative curve of early flow stages rised which was similar to the effect of a larger skin factor. The radius of region-1 and region-2 mainly had an influence on the starting time of transition stage and the duration of radial flow. When the radius of region-1 and region-2 was larger,the start time of the transfer stage was prolonged. When M12 was enhanced,the pressure of the flow in both region-2 and region-3 was larger. When M23 was enhanced,the pressure of the flow in region-3 elevated.