Lithologic Reservoirs

Thick and broad lacustrine carbonate sediments developed in the upper member of the lower Ganchaigou Formation(E32)in western Qaidam Basin. Multiple oil-bearing series were found in Shizigou area and many oil wells with high yield were drilled. In order to further explore the characteristics and distribution rules of lacustrine carbonate reservoir,the data of logging,seismic,core observation and reservoir test analysis,were used to study the geochemical characteristics,structure types,sedimentary characteristics and main controlling factors of sedimentary facies distribution of lacustrine carbonate rocks. The result shows that the lacustrine carbonate rocks in western Qaidam area are composed of mixed sedimentary rocks,and the lithologies are mainly calcitic dolomite and marl,followed by dolomite and limestone. The structural components of carbonate rocks are mainly mud-crystal and crystallite dominate,followed by particles. The sedimentary microfacies are mainly marl flats and calcite dolomite flats,followed by algal banks and oolitic banks. The lithologic assemblage is mainly affected by palaeogeomorphology,paleo-fluid and paleoclimate. Local salinization lacustrine environment,semi-closed salinization lacustrine environment and open salinization lacustrine environment are developed in the study area. The high-quality carbonate reservoirs are formed by the common action of different sedimentary environments and sedimentary models.

Controls of syndepotitional structural slope-break zones on sequence architecture and enrichment zones of lithologic reservoirs in northwestern margin of Junggar Basin

FENG Youliang, HU Suyun, LI Jianzhong, CAO Zhenglin, WU Weian, ZHAO Changyi, CUI Huajuan, YUAN Miao

2018, Vol.30(4): 14–25 Abstract ( 315 ) PDF (9839 KB) ( 649 )

doi: https://doi.org/10.12108/yxyqc.20180402

The western margin of Jungger Basin is a petroliferous structural belt,and lithostratigraphic reser-voirs are dominant exploring targets. Syndepositional structural slope-break zone has a strong control effect on sequence architecture and enrichment zones of lithologic reservoirs. On the basis of seismic,drilling and logging data,according to the method of structural sequence analysis,the characteristics of syndepositional structural slope-break zones in the study area and its controlled sequence architecture were studied. The results show that the syndepositional slope-break zones developed in the study area can be divided into two types,namely,the slope-break zone controlled by syndepositional reverse faults and flexure slope-break zone controlled by buried fault,according to the origin. The former is the gradient abrupt zone of lake bed caused by syndepositional reverse fault movement,while the later is the gradient abrupt zone of lake bed resulted by seated-reverse-faults. During Middle to Late Permian period,the study area was in the transition stage from rifted basin to down-warped basin, slope break zones controlled by syndepositional reverse faults and sequence architecture controlled by them were developed. Since Triassic to Paleogene period,the study area was in the compressional down-warped stage, slopebreak zones controlled by syndepositional reverse faults,flexural slop-break zones controlled by buried fault,and sequence architecture controlled by them,were developed. The sequence architecture controlled by syndepositional reverse faults slop-break zone shows that the lowstand systems tract is composed of alluvial fans and braided river deposited at the upward of the zone,and the braided deltas developed at the downward of the zone,the expanding systems tract consists of floodplain,shallow lake and retrogradational deltaic sediments at the upward of the zone,shallow to deep lake deposits at the downward of the zone,and highstand systems tract comprises of fluvial deltas. The sequence architecture controlled by flexural slope break zone is characterized by incised infills deposited at the upward of the flexural slope break zone and shallow lake or lowstand braided deltas deposited at the downward of the zone within lowstand systems tract,shallow to half deep lake developed in expanding systems tract,and fluvial deltaic and shore to shallow lake deposited within highstand systems tracts. Lowstand conglomerate bodies and sand bodies in sequences,such as alluvial fans,deltas of lowstand and sand bodies of shore and shallow lake,have good conditions for hydrocarbon accumulation and are favorable for enrichment of lithologic reservoirs.

Controlling of epimetamorphic rock lithology on basement reservoir and identification of lithological sequence of reservoir in Hailar Basin

LI Juan, SUN Songling, CHEN Guangpo, ZHANG Bin, HONG Liang, HE Weiwei

2018, Vol.30(4): 26–36 Abstract ( 404 ) PDF (62589 KB) ( 544 )

doi: https://doi.org/10.12108/yxyqc.20180403

Lithology identification is the key and base work to study metamorphic rock basement reservoirs. Taking the complex epimetamorphic rock basement of Budate Group buried hill in Beir Sag,Hailar basin as an example, the core,thin slice,well log and seismic data were used to establish the log-seismic response standards of the main lithologies through the method of well log crossplot and seismic facies analysis. The controlling effects of lithology on reservoir spaces such as structural fractures and dissolved pores were illuminated,from the aspects of different reform degree by weathering-leaching and faulting effects. According to quantitative statistics of lithologies,reservoir physical properties and oil production,the hierarchical-related correspondence of reservoir and lithological sequence was built. The geophysical methods of seismic spectrum clustering and multi-attribute neural network clustering were applied to predict the distribution of lithological sequence of reservoir. The results show that there are five main types and nine fundamental lithological rocks developed in Budate Group, which have specific well log response values and seismic reflection characteristics. The differences in mineral composition and content,weathering resistance,and rock strength for each lithology control the difference of reservoir type and quality. The lithological sequences of reservoir compose of four levels. The levelⅠis pyroclastic sedimentary rocks and normal medium-fine sedimentary rocks, which is good reservoir, with oil production more than 15 t/d,the level Ⅱ is pyroclastic rocks,which is fair reservoir,with oil production of 1-15 t/d,the level Ⅲ is sedimentary pyroclastic rocks and normal mudstone,which is medium reservoir,with oil production less than 1 t/d, and the level Ⅳ is intermediate-basic volcanic rocks, which is poor reservoir, being dry layer. The high quality reservoirs in the study area are mainly developed in the well fields of Bei 15,Bei 38 and Bei 32,and the eastern and central Talaham structural zone.

Lithologic reservoir forming conditions and its exploration implication in northern Melut Basin,South Sudan

WANG Guolin, SHI Zhongsheng, ZHAO Yanjun, CHEN Bintao, XUE Luo

2018, Vol.30(4): 37–45 Abstract ( 408 ) PDF (2390 KB) ( 452 )

doi: https://doi.org/10.12108/yxyqc.20180404

After more than ten years of exploration in northern Melut Basin,the remaining structural traps are limited and small,which is difficult to meet the exploration demands,and the exploration field should be transferred to the field of lithologic reservoir. With wire-logging,mud-logging and coring data from near 200 exploration wells and more 4 000 km2 3D data,the source rock evaluation,sedimentary facies and fault features were researched,the results show that:firstly,the northern Melut Basin consists of Jamous,Abyat,Moleeta and Ruman depressions acting as four active oil kitchens and presents sufficient oil source. Secondly,interbedded sandstone and mudstone of delta front developed in Cretaceous Galhak Formation and Tertiary Yabus Formation,which is favor-able to form lithological traps. Thirdly,faults could enhance the oil charging for Galhak Formation as insource reservoir and act as migration pathway for upper member of Yabus Formation as above-source reservoir. The research shows that northern Melut Basin has the geologic conditions for forming lithologic reservoirs and guides a series of exploration discoveries of lithologic reservoirs,such as up-dip pinchout lithologic reservoir of Galhak Formation in Ruman area and structural-lithologic composite reservoir of Yabus Formation in Gasab area, which strongly promotes the exploration and deployment of lithologic reservoirs in northern Melut Basin.

Controlling of paleogeomorphology to characteristics and distribution of karst structures of Yingshan Formation in Tazhong area

GENG Xiaojie, LIN Changsong, WU Bin

2018, Vol.30(4): 46–55 Abstract ( 355 ) PDF (9751 KB) ( 526 )

doi: https://doi.org/10.12108/yxyqc.20180405

Paleogeomorphology is one of the important external factors for the development of karst reservoir of Yingshan Formation in Tazhong area. Based on fine interpretation of seismic section,stratigraphic trend extrapolation method was adopted to restore the geomorphology after the deposition of Yingshan Formation,the karst geomorphic units were divided and the karst sections of different geomorphic units were dissected. The results show that there are three types of karst profiles including surface caves,interlayer-vadose zones and vadose-phreatic zones induced from karst structures. The distribution of paleogeomorphology units is controlled by the structural belts to a great extent. Karst highland is located in the No. 10 fault belt primarily. It is the main recharge area of groundwater with developing large karst caves. The beaded reflections on the seismic profile are this kind of structure. There is karst slope area between No. 1 and No. 10 faulted belts. It is the lateral recharge area of groundwater. The direction of water flow is from vertical seepage to groundwater flow. Hyporheic zone caves and fractures mainly developed in this area. There are basically not karst reservoirs in the karst depression area. This geomorphic pattern promotes the natural migration of dissolution fluid from the high potential region to the low and provides favorable tectonic settings for continuous development of karst reservoir.

Reservoir characteristics of Chang 6₁ and its control on oil-bearing ability in Dingbian-Wuqi area,Ordos Basin

YAO Jingli, LI Yong, CHEN Shijia, QIU Wen, SU Kaiming, HE Qingbo

2018, Vol.30(4): 56–64 Abstract ( 320 ) PDF (39257 KB) ( 428 )

doi: https://doi.org/10.12108/yxyqc.20180406

Chang 61 reservoirs distributed in Dingbian-Wuqi area are obvious zoning with clear major controlling factors. Core observation,a number of fluorescence images,cast sections,scanning electronic microscope observation,mercury injection data and physical property data were used to analyze the differences of physical property,sand body thickness and mudstone content of Chang 61 reservoir among different blocks,to determine the influencing factors of gas-bearing ability differences. The results show that it is characterized by low porosity and low permeability with intergranular pores and feldspar solution openings developed. Reservoir characters are obviously divided according to districts. The contents of quartz,debris and matrix increase while feldspar content decreases from eastern part to western part where the physical properties are poor. Eastern part has the best physical properties with low displacement pressure and good pore structure while intersection area in the middle has the worst physical properties. It is demonstrated that oil-bearing ability differences are closely associated with reservoir zoning characters. Sand bodies in eastern part are characterized by great thickness,low shale content,good physical properties and best oil-bearing ability. Because of the counteract of water power and fast accumulation of shale, the intersection area where the physical properties are poor with thin sand bodies and lamina is mainly consist of water wells. Reservoir oil-bearing ability is mainly affected by sands body thickness,shale content and reservoir properties. This research has some references for the next exploration.

Reservoir accumulation characteristics of Jurassic Yan'an Formation in Yanwu area, Ordos Basin

YE Bo, LIANG Xiaowei, SONG Juan, CAO Runrong, MAO Zhenhua, HAO Bingying

2018, Vol.30(4): 65–73 Abstract ( 452 ) PDF (15294 KB) ( 554 )

doi: https://doi.org/10.12108/yxyqc.20180407

The reservoir of Jurassic Yan'an Formation is characterized by small scale, complex forming characteristics and it is difficult to predict in Yanwu area, Ordos Basin. In order to make clear the main accumulation time and whether there is a secondary migration accumulation in geological history period, and to provide theoretical basis for exploration, the reservoir accumulation characteristics of Jurassic in Yanwu area was studied through testing means such as quantitative grain fluorescence, fluid inclusions and so on. The results show that the ancient oil-water interface rise and hydrocarbon dissipation had ever happened in Yan'an Formation. Some of the reservoirs had suffered damage or the secondary hydrocarbon migration had happened in geological history period.The reservoir accumulation period of Yan'an Formation in Yanwu area can be mainly divided into two stages. The early accumulation stage was at the end of Early Cretaceous, and the oil accumulation was mainly in the lower layers of Yan'an Formation. The late accumulation stage resulted by tectonic uplift was since Upper Cretaceous, and the oil accumulation was in the upper layers of Yan'an Formation. The accumulation range of the late stage is more far away from Chang 7 hydrocarbon generation center than the early stage. The present reservoir distribution pattern ofYan'an Formation inYanwu area was formed jointly by the two accumulation stages.

Stratified constrained near-surface model building method and its application in complex surface area

WANG Xiao, LIU Wenqing, ZENG Huahui, YANG Wei

2018, Vol.30(4): 68–73 Abstract ( 326 ) PDF (52876 KB) ( 510 )

doi: https://doi.org/10.12108/yxyqc.20180408

With the development of petroleum exploration,lithologic and low-relief structure reservoirs become more and more important. For low-relief structure,besides the inherent factor of stratigraphic lithology,the key factor that influences low-relief structures is the long-wavelength statics. The main reasons resulting in the longwavelength statics are the relative low precision of the near-surface velocity model and the inaccurate space depiction of low-velocity bottom interface in complex surface area. The near-surface velocity model was built using stratified constrained model building method. Firstly,the accurate low-velocity layer model was built using micrologging data,and then the descending-velocity layer model was built using short-refraction and vertical seismic profile(VSP) data,so as to obtain the initial model of global optimization nonlinear near-surface tomography. Nearsurface velocity model with high precision can be built by using the stratified constrained tomography method. Based on the VSP and measured well depth constraints,the space morphology of the interface of the descending-velocity layer was optimized by cokriging method. Through the above two strategies,the long-wavelength static correc tion problems in complex surface area were well solved,and good application results were achieved in litho-logic reservoir exploration in X area of Mahu Sag,Junggar Basin.

Evaluation of shale gas resource potential of Late Permian Dalong Formation in western Hubei province

YU Jianghao, WANG Deng, WANG Yi, XIE Tong, SHI Xianbin, CHEN Wei

2018, Vol.30(4): 84–90 Abstract ( 427 ) PDF (9522 KB) ( 515 )

doi: https://doi.org/10.12108/yxyqc.20180409

The exploration breakthrough of Cambrian and Precambrian shale gas in Zigui area,Yichang,Hubei province,shows favorable exploration prospects for shale gas in western Hubei province. The western region of Hubei province is the key area for shale gas exploration and development and is also the most likely area to achieve a commercial breakthrough of shale gas. Field profile survey and correlation,old well reexamination, geochemical and gas-bearing property analysis of shale samples were carried out. It is considered that it was mainly basin sedimentary environment in the Late Permian Dalong Formation in Jianshi-Hefeng area. The effective thickness of the deposited black shale is about 30 m,and the hydrocarbon generation material basis is fine. The shale gasmass volume of Dalong Formation is more than 2 m3/t,and the average shale gas mass volume of the shale samples measured by isothermal adsorption experiment reaches 2.58 m3/t. showing favorable prospects of shale gas exploration. The Permian Dalong Formation in western Hubei is most likely to be a new demonstration area for shale gas exploration in Hubei province since the demonstration area of Cambrian and Precambrian in Zigui region, which is expected to open up a new situation of shale gas exploration and development in Hubei province.

Grid tomography based on well-to-seismic integration in anisotropic velocity modeling and its application

HAN Linghe, HU Ziduo, FENG Huiyuan, LIU Wei, YANG Zhe, WANG Yanxiang

2018, Vol.30(4): 91–97 Abstract ( 315 ) PDF (48636 KB) ( 497 )

doi: https://doi.org/10.12108/yxyqc.20180410

Estimation of anisotropic velocity and parameter is a key technology in the success of anisotropic prestack depth migration in real seismic data processing. It is one of the commonly used methods to calculate the anisotropic parameters by well-to-seismic integration for seismic data processing at present. The conventional well-to-seismic integration method can be used to obtain anisotropic parameters by comparing the formation thickness,but the accuracy is low and cannot meet the geological requirements. Grid tomography based on wellto-seismic integration was applied to anisotropic velocity modeling in 3D VTI media. The anisotropic velocity and parameters of each grid were updated along the ray path,and the accuracy of velocity model was further improved by iterative calculation. The application results show that compared with conventional well-to-seismic integration method,grid tomography based on well-to-seismic integration can greatly improve the precision of anisotropic velocity and parameters and enhance the consistency of depth migration results and well logging data. Moreover,the common imaging point gather of long offset is more flatten,which can provide more information of long offset for prestack inversion, and the local imaging effect of the migration results is also improved effectively.

Reservoir prediction based on seismic waveform classification in time-frequency domain

SHI Zhanzhan, WANG Yuanjun, TANG Xiangrong, PANG Su, CHI Yuelong

2018, Vol.30(4): 98–104 Abstract ( 493 ) PDF (5552 KB) ( 540 )

doi: https://doi.org/10.12108/yxyqc.20180411

There are two problems in the reservoir prediction:(1)The traditional time-frequency analysis method is influenced by Heisenberg uncertainty principle or cross-terms,so it is often difficult to meet the requirements of high resolution.(2)The traditional time-frequency analysis method increases the redundancy of signal and increases the interpretation workload. Aiming at these two problems,a reservoir prediction method based on timefrequency domain seismic waveform classification was proposed. This method performs time-frequency decomposition of seismic signal by synchroextracting transform,and it corresponds to decomposing the complex signals into a series of simple waveforms(different frequencies and time shifts)superimposed. The decomposition results were classified by generative topographic mapping,and the waveform classification results were further calibrated by logging and drilling data. The practical applications indicate that the seismic signal waveform changes can be effectively detected by the reservoir prediction method combined with the synchroextracting transform and the generative topographic mapping.

Multi-level fuzzy identification method for interwell thief zone

HUANG Bin, XU Rui, FU Cheng, ZHANG Wei, SHI Zhenzhong

2018, Vol.30(4): 105–112 Abstract ( 318 ) PDF (3342 KB) ( 456 )

doi: https://doi.org/10.12108/yxyqc.20180412

In order to correctly identify and evaluate the development of the thief zone, and take appropriate blocking measures, considering the complexity and fuzziness of the identification process of the thief zone, a multi-level fuzzy comprehensive evaluation index system(AHP-FCE)based on AHP and fuzzy comprehensive evaluation method was proposed. The evaluation index system consists of three evaluation object subsystems and 25 evaluation indicators, and the interwell connectivity is represented by grey relational degree. The model was applied to the identification of the thief zone in the S14 layer of N oilfield, and three evaluation levels of primary thief zone, secondary thief zone and normal pore channel were established. The weight of each factor was determined by entropy weight method, and the membership degree matrix was calculated by choosing semi trapezoid membership function. According to the principle of maximum membership degree, the thief zone of each interwell was evaluated. The results show that there are 16 primary thief zone and 10 secondary thief zone, and the development of the thief zone is more obvious between the interwells with high permeability and imperfect well pattern relations. The identification results were verified by the well tracer method, and the accuracy rate was 87.5%. The results show that this method is reasonable and accurate, and can provide a clear guidance for profile control or water shut off in the later stage of oilfield.

Calculation of phase behavior for CO₂-water mixtures using CPA EoS

TU Hanmin, GUO Ping, JIA Na, WANG Zhouhua, WANG Qian

2018, Vol.30(4): 113–119 Abstract ( 279 ) PDF (1521 KB) ( 589 )

doi: https://doi.org/10.12108/yxyqc.20180413

Carbon dioxide(CO2)is an acid gas, and its thermodynamic properties are vital to numerous processes in the oil and gas. Water always coexists with hydrocarbons in petroleum reservoirs, and the presence of brine may reduce the amount of gas to be mixed with hydrocarbons. This effect increases with increasing pressure and the amount of aqueous phase(while decreases with the decreasing of salinity). Hence, the understanding of the thermodynamics of CO2-water mixtures is quite crucial for the rational design and operation of many processes. The characteristics of phase behavior for CO2-water mixtures were studied by using Cubic-Plus-Association (CPA)Equation of State(EoS)to combine with the CR-1 mixing rule to assess the mutual solubility of CO2 and water. CO2 can be treated in three different ways:(1)as a non-associating molecule; (2)as an associating molecule that can be cross-associate with water(solvation);(3)as a self and cross associating molecule. As water is considered as an associating molecule,it has three association schemes of 2 B, 3 B and 4 C. The performance of CPA EoS using different interaction models was evaluated and discussed at three temperatures of 308 K, 373 K and 473 K, and also was compared to various recent published investigations. It demonstrates the complicated phase behavior of CO2 and water, especially when they are close to the critical point of CO2, where thermodynamic properties sudden changed. The results show that good agreement with experimental data can be achieved when CO2 is considered as a non-associating molecule and 4 C association scheme is considered in the calculation model.

Development models for offshore heavy oil field in high water cut stage

ZHANG Yunlai, LIAO Xinwu, HU Yong, LI Tingli, SU Jinchang

2018, Vol.30(4): 120–126 Abstract ( 385 ) PDF (5887 KB) ( 760 )

doi: https://doi.org/10.12108/yxyqc.20180414

After entering high water cut development stage,the offshore heavy oil field is faced with the problems of low oil recovery speed,rapid water channeling,rapid production decline and low recovery ratio,and lack of experience in stratified development and adjustment,which restricts the stable production and efficient development of the oil field. Taking Qinhuangdao 32-6 oilfield as an example,the development model in high water cut stage was studied by using laboratory physical experiments and reservoir numerical simulation,and the technical limits of stratified development of offshore heterogeneous heavy oil reservoirs,injection-production infill model and downhole limit of horizontal well layout in bottom water reservoir were defined. The results show that when the reservoir viscosity level difference is less than 3 or the permeability difference is greater than 3,the interlayer interference coefficient increases,the stratified development should be carried out,and the thickness of each development layer is 4-8 m. For strong heterogeneous reservoirs,the volumetric sweep efficiency varies greatly under different well types and pattern infill models. By adjusting the well spacing to 220 m,the volumetric sweep efficiency is improved significantly. The permeability,distribution area and distribution position of reservoir interlayer have great influence on the productivity of horizontal well. After the interlayer optimization,the accumulative oil production of the horizontal well in the heavy oil bottom water reservoir with the viscosity of 260 mPa·s is 50 000 m3, and the height of the oil column can be pushed from 12 m to 7 m. Based on the above research results, a new high efficiency development model of"vertical layering system", "plane change well pattern"and"horizontal well tapping potential" in offshore fluvial facies oil fields was formed. It was applied to Qinhuangdao 32-6 oilfield, and good results have been achieved, which can provide reference for the development of similar oilfields.

Application of new cold production technology through mixing light oil by commingling for high pour point reservoir

DOU Songjiang, LI Lianmin, SHI Depei

2018, Vol.30(4): 127–132 Abstract ( 320 ) PDF (1384 KB) ( 610 )

doi: https://doi.org/10.12108/yxyqc.20180415

High pour point crude with the features such as high freezing point and poor flowing ability resulted in poor economic performance when producing in this kind of reservoirs, so a new cold production method through mixing light oil by commingling was developed for high pour point reservoirs, which integrates the techniques such as wellbore thermal conduction, mixing light oil to increase liquid production rate and lowering pour point and considers the factors of formation temperature, liquid production rate, mixing ratio and operating parameters of wells. The sensitivity of the above mentioned factors was also analyzed. The results show that liquid rate and wellhead temperature could be increased through mixing light oil and wellhead temperature would be high enough when liquid rate was above 60 m3/d. Pour point of crude would be decreased a lot when ratio of light oil over liquid rate was over 60%. Fluid level affected temperature loss apparently, and wellhead temperature would keep high if fluid level was deeper than 1 000 meters. The technology was applied in G oilfield and achieved good results that cumulative oil of 3.16×104 m3 in one producer which were unavailable by conventional method was produced within 1.5 years. The research shows that the method presented above could be used successfully in producing oilfields with both light oil and high pour point oil based on optimizing liquid rate, mixing ratio and operating parameters of producers, and it will be good reference for the development of the same kind of reservoirs.

New method for obtaining reservoir parameters with a short time of pressure drop after mini-fracturing

ZHANG Jian, JING Jiyun, WANG Xingzun

2018, Vol.30(4): 133–139 Abstract ( 268 ) PDF (1522 KB) ( 409 )

doi: https://doi.org/10.12108/yxyqc.20180416

Initial reservoir pressure and effective permeability are important parameters for reservoir evaluation, fracturing design and well proration of tight reservoirs. Traditional well testing methods and DFIT method are not applicable for tight reservoirs because of the long test time. So a new method for obtaining reservoir parameters quickly with a short time of pressure drop after mini-fracturing was prospered:calculating initial reservoir pressure by identifying pseudo-linear flow regime after fracture closure accurately,and achieving the effective reservoir permeability by simulating and fitting post-fracturing pressure drop curve on the foundation of filtration analysis. At last,the calculation result indicates that this method can be used to obtain the reservoir parameters accurately and shorten the test time greatly.

Volume fracturing parameters optimization of horizontal well in tight reservoir

SU Hao, LEI Zhengdong, ZHANG Diqiu, LI Junchao, JU Binshan, ZHANG Zeren

2018, Vol.30(4): 140–148 Abstract ( 398 ) PDF (6894 KB) ( 669 )

doi: https://doi.org/10.12108/yxyqc.20180417

The technique combining horizontal well with volume fracturing is an important way to obtain commercial oil flow in tight reservoir. In order to optimize the volume fracturing parameters of horizontal well which influence its development effects,based on the numerical simulation method of discrete fracture model,the more flexible unstructured grid was used to establish simulation models of volume fracturing for horizontal well, which can explicitly characterize the geometric parameters of complex fractures and the flows inside,verified by the Eclipse software and the actual mine well data. By referring to the parameters of tight reservoir in Changqing Oilfield,the parameters of the horizontal well such as orientation,fracture arrangement,stage spacing,cluster spacing and SRV were optimized. The results show that the development effect is best when the orientation of horizontal well is parallel to the orientation of natural fractures. The optimal sorting of fracture arrangement type is dumbbell-type,staggered-type,uniform-type and spindle-type. The stage spacing should be longer than sum of drainage radius of both two adjacent stages,so as to eliminate the interference among the stages. The cluster spacing should be as long as possible without excess the average length of natural fractures. When SRV is constant,the longer the length of stimulated areas,the better the development effect will be. When the length of the stimulated fracture is difficult to increase restricted by technology,increasing the number of cluster could improve the well productivity as well,and the more clusters there are,the highest of initial cumulative production can be expected,nevertheless,the optimal cluster number depends on well planned production time. The research results can provide a basis for the design of fractured horizontal wells in tight reservoirs.

Influences of bedding planes on mechanical properties and prediction method of brittleness index in shale

WANG Yuepeng, LIU Xiangjun, LIANG Lixi

2018, Vol.30(4): 149–160 Abstract ( 366 ) PDF (38503 KB) ( 310 )

doi: https://doi.org/10.12108/yxyqc.20180418

In order to study the mechanism of the effects of bedding planes on the mechanical properties of shale, we carried out the following related experimental researches. After observing the shale samples taken from Long-maxi Formation in Jiaoshiba area in Sichuan Basin by polarizing microscope and scanning electron microscopy, we got that the shales are rich in bedding planes, micro-fractures and micro-pores. The clay minerals are arranged in a directional arrangement, and the cementations of the layers are weak. RFPA numerical simulation basic parameters were acquired by the results of uniaxial physical compression experiments at different bedding plane angles. These are the basis on which the influence of bedding plane angles, the densities of bedding panes and the mechanical properties of bedding planes on uniaxial compressive strength, elastic modulus, Poisson's ratio and brittleness can continue to be studied by using digital simulation method. A new prediction method for shale brittleness index was presented by statistical methods when we only know the densities of bedding planes, the angles of bedding planes, uniaxial compressive strength and the mechanical properties of bedding planes. Numerical simulation experiments results indicated that the characteristics of uniaxial compressive strength and brittleness index at different angles of bedding plane roughly showed the U-shaped changing trend. The maximum value occurred at the bedding plane angles of 0° and 90°, whereas the minimum value occurred at the bedding plane angle of 45°. The elastic modulus of shale decreased with the increase of bedding angles, then increased and then decreased, finally increased. With the increase of bedding plane angles, the value of Poisson's ratio firstly decreased, then increased and finally decreased. And Poisson's ratio got the minimum value at bedding plane angle of 30°, whereas the maximum value at bedding plane angle of 70°. Elastic modulus, uniaxial compressive strength, and brittleness index overall decreased with the increase of the density of bedding planes. Poisson's ratio showed different states at the different bedding plane angles with the increase of the density of bedding planes. The types of rock fracture of uniaxial physical compression experiments are different at different bedding plane angles. The strength parameters, elastic parameters, brittleness and fracture modes all showed very strong anisotropy. The study about the influence of bedding planes on the mechanical properties and the prediction of brittleness in shale can provide a necessary technical foundation for the stability of shale gas wells and rational development of shale gas.