Table of Content

26 April 2010, Volume 31 Issue 2

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Strategic concepts of accelerating the survey,exploration and exploitation of shale gas resources in China

ZHANG Da-Wei-

2010, 31(2):  135-139+150.  doi:10.11743/ogg20100201

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This paper introduces the world's shale gas resource potential and the trend of its exploration and exploitation.The author also discusses China's shale gas resource potential and current status of exploration and exploitation.Based on this information,this paper puts forward some strategic concepts of accelerating the survey,exploration and exploitation of shale gas resources in China: 1) to conduct a nationwide survey on shale gas geology and potential,to recognize favorable plays and E&P areas,and to establish pilot areas for shale gas exploration and exploitation;2) to do research on the accumulation and pooling patterns of shale gas,to advance innovation of shale gas exploration and exploitation techniques and to set up a technical system which could support shale gas exploration and exploitation;3) to build talent teams for shale gas survey,exploration and exploitation and to develop a geological data sharing system and a social service system;4) to draw up a plan for shale gas survey,exploration and exploitation,to establish an incentive system for shale gas exploration and production,to perfect the mining rights management system,to reinforce international cooperation and exchange and to establish standards and specifications of shale gas technologies.

Tectonic features of the Subei Basin and the forming mechanism of its dustpan-shaped fault depression

CHEN An-Ding-

2010, 31(2):  140-150.  doi:10.11743/ogg20100202

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The Subei Basin is a typical dustpan-shaped fault depression composed vertically of three layers,i.e.,a downwarped basin deposit(K2t-E1f),a fault depression basin deposit(E2d-E2s) and a tilt-block basin deposit(N1-2y).The basin had gone through three episodes of uplifting and is a relic basin formed in the late Early Tertiary.It also developed some fault combinations of different types and NE-and NW-trending structures.This paper documents a discussion on the forming mechanism of the dust-shaped fault depression,and comes to the conclusion that the tilting in the depression is the least likely to be caused by "rotation",and that the numerous extensional faults were resulted from the early reverse faulting of the basement and the reversing of force couple.The present dustpan-shaped basin is the result of deposition or uplifting and erosion when experiencing extension,faulted depression and compression at the same direction,alternating with basement uplifting.The dynamic of the extension and compression mainly came from the subduction and collision of the India Plate and the Pacific-Philippine plate to the Eurasia.With the two forces alternatively working on the eastern China,an "accordion-like" stress field(with extension and compression alternated) was formed in the NW direction,resulting in the dustpan-shaped basin

An analysis of structure evolution and reservoiring conditions in the Bodong low salient of Bohai Basin

WANG Ying-Bin, WANG Hai-Jun, SUN He-Feng-

2010, 31(2):  151-157+179.  doi:10.11743/ogg20100203

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The Bodong low salient is located in the central-north part offshore Bohai bay.It is a narrow N-E trending strip appearing as a horst with two faults sandwiching an uplift on the E-W section.Three sets of fault systems shape the salient into a complex structure with the deep layer being segmented in E-W direction and shallow layers being zoned in N-S direction.The salient experienced three evolution stages: the forming period,the strike-slip structure development period,and the neotectonics period.The unique geographical position of the salient played a determinant role in forming reservoirs with favorable pooling conditions.It has three hydrocarbon kitchens,three sets of reservoirs,three kinds of carrier system,and three types of traps as well as good seals,all of which provide favorable conditions for hydrocarbon pooling.

Sequence stratigraphic characteristics of the Paleocene lithologic and stratigraphic reservoirs in the Dongying Depression

WANG Hua-Ai-

2010, 31(2):  158-164.  doi:10.11743/ogg20100204

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In this paper,sequence stratigraphic theories are used to analyze the hydrocarbon pooling factors and distribution pattern of the Paleocene lithologic and stratigraphic reservoirs in the Dongying Depression.According to the study,the sequence stratigraphy has a major control on the hydrocarbon pooling factors of the lithologic and stratigraphic reservoirs,such as hydrocarbon generation,preservation,sealing,migration and accumulation.Lithologic and stratigraphic reservoirs are mainly distributed below slope break,near unconformity surface or near flooding surface.System tracts and sedimentary base level cycle control the types of reservoirs: stratigraphic re-servoirs mainly occur in the lake transgression system tract,while lithologic reservoirs are mainly found in low system tract and high system tract.The pool-forming efficiencies are different for sandbodies on different orders of sequence boundaries.

Depositional characteristics and hydrocarbon exploration significance of shallow deltas in the Yellow River Mouth Sag

WU Xiao-Hong, LV Xiu-Xiang,ZHOU Xin-Huai, ZHANG Jie, SHI Cui-E-

2010, 31(2):  165-172.  doi:10.11743/ogg20100205

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The hydrocarbon reservoirs in the Neogene shallow deltas are the main type of recent discoveries in Bohai Sea.Using various data such as depositional facies analysis,grain size,paleontological marker and paleoenvironment response,we have summarized the sedimentary characteristics and development settings of the shallow deltas,determined their distribution pattern and controls and discussed their favorable conditions of hydrocarbon accumulation.The study results show that:1) these shallow deltas developed in shallow and gentle lakes;2) multiple stages of sand-mud interbedding occurred due to the periodical changes of lake level;3) as the main sedimentation type in these deltas,the sublacustrine distributary channels are stable in their regional distribution.These depositional characteristics may lead to good reservoir-seal combinations in the shallow deltas,and the associated later strike-slip faults are favorable to developing various traps,with sufficient oil sources and an unobstructed hydrocarbon migration.Therefore,these shallow deltas are good in hydrocarbon accumulation conditions and are great in exploration potential.

A fossil oil-reservoir and the gas origin in the Lower Sha-4 Member of the Well Fengshen-1 area,the North Dongying zone of the Jiyang Depression

LI Yan-Jun, SONG Guo-Qi, LI Wen-Tao, GUO Rui-Chao, YANG Xian-Cheng, CHEN Yi-Cai, LUO Wen-Jun-

2010, 31(2):  173-179.  doi:10.11743/ogg20100206

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The deep interval of Lower Sha-Member 4 is characterized by producing condensate oil and gas in the Well Fengshen-1 area,the North Dongying zone,Bohai bay Basin.According to a comprehensive analysis of hydrocarbon gas composition,nitrogen content,gas carbon isotope,microfluorometric reservoir section and thermal simulation experiment,it is revealed that the gas in this area belongs to a type of crude-cracked gas,and that pyrobitumen generated by thermal alteration occurs widely in the reservoir pores.In combination with the geothermal history of the reservoir rocks and hydrocarbon generation history of the source rocks,it can be verified that a latest Paleogene(Es1)fossil oil-reservoir existed in the deep Sha-Member 4 sandstone-conglomerate body,the oil in which was thermally cracked from Neogene Minghuazhen to the present time(Nm-Q),resulting in the formation of a deep condensate gas reservoir.It is also found that a type of gas mixed by source-kerogen-cracked gas and oil-cracked gas occurs along the fossil oil-reservoir margin,such as the Well Fengshen-3 area,and that a lot of releasing microfractures in the reservoir rocks are the main factor to maintain a normal pressure system in the condensate gas reservoir.

Controlling effects of volcanic rocks upon gas pools —taking two volcanic gas reservoirs in the Sonliao Basin as examples

SUN Fen-Jin, LUO Xia, QI Jing-Shun, SHAO Ming-Li, ZENG Fu-Ying, JIANG Xiao-Hua, HAO Cui-Guo-

2010, 31(2):  180-186.  doi:10.11743/ogg20100207

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The research documented in this paper takes the Xingcheng and Shengping volcanic reservoirs in the Xujiawuzi fault depression in the deep of the Songliao basin as study targets. It focus on the controlling effect of the volcanic bodies upon the horizontal and vertical distribution，waterˉgas relationship，caps，pooling types of the gas reservoirs. Thanks to the volcanic bodies，these reservoirs have wide vertical distributions and can occur in a depth up to 4000 to 5000 meters and show features of vertical superimposition of multiple gas reservoirs and lateral beaded distribution. The gasˉwater relationship in the volcanic gas reservoirs is complicated and controlled by the volcanic bodies and eruption periods. Each volcanic body owns isolated gasˉwater systems，but with initor within the same well，there may be several gasˉwater systems. Volcanic gas reservoirs feature in selfˉaccumulation and selfˉsealing and therefore regional seals are not the major condition for hydrocarbon pooling. In general，there are four types of volcanic reservoirs. Among them，the structuralˉlithologic complex gas reservoirs are predominant and controlled mainly by lithology and occur mostly at the structural highs，while the lowˉamplitude anticli nalˉlithologic complex gas reservoirs can only be found in volcanic rocks. They are harbored in a kind of specific anticline formed during volcanic eruptions.

Features of source rocks and hydrocarbon pooling in the Kelameili gas field，the Junggar Basin

DA Jiang, HU Yong, ZHAO Meng-Jun, SONG Yan, XIANG Bao-Li, QIN Sheng-Fei-

2010, 31(2):  187-192.  doi:10.11743/ogg20100208

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In this paper，an analysis is made on the source rock features，source of hydrocarbons and gas pooling process in the Kelameili gas field of the Junggar Basin in Xinjiang. Using techniques such as source rock analysis，hydrocarbonˉsource correlation and comprehensive analysis of hydrocarbon pooling，we describe the main source rocks of the Kelameili gas field and preliminarily determine the gas accumulation process and its main controlling factors. According to the study，it is believed that:1）the main source rock of the Kelameili gas field is the Carˉboniferous source rock;2）hydrocarbons mainly accumulate in reservoirs near the source rocks and the pooling process is characterized by“early accumulation and late preservation”;3）multiˉstages of charging happened in the Late Hercynian，Late Indonisian and MiddleYanshanian;4）hydrocarbon pooling in different areas has a temporal sequence. The main controlling factors for gas pooling in the Kelameili gas field are the distribution of Carboniferous source rocks and volcanic rocks as well as the regional seals in the Permian Urho Formation.

Palaeoˉformation pressure evolution and episodic hydrocarbon accumulation in Tao’erhe Depression，Chezhen Sag

ZENG Zhi-Ping, HAO Fang, SONG Guo-Qi, SUI Feng-Gui-

2010, 31(2):  193-197+205.  doi:10.11743/ogg20100209

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In Tao’erhe Depression，abnormally high pressure is generally developed and its evolution is inherently connected with hydrocarbon generation，migration and accumulation. The various periods of formation pressure evolution and the episodic hydrocarbon generation，migration and accumulation can be effectively determined by restoring paleo formation pressures and making a comparison among divisions of thermal evolution stages of organic matter. The flow patterns of formation fluids are identified in the different periods of pressure evolution. In Chezhen Sag，there were2processes of overpressure accumulation and release during the formation pressure evolution，with the microfractures formed during the early overpressure accumulation becoming the main pathway for primary hydrocarbon migration. The secondary pores and microfratures formed during the late overpressure accumulation can serve as the pathway for great secondary hydrocarbon migration and the space for hydrocarbon accumulation.

An application of 3D structural modeling to complex fault-block reservoirs——a case of the lower unit reservoir of Sha-3 Member in Block Wei-95,Mazhai Oilfield,Dongpu Depression

CUI Ting-Zhu, MA Xue-Ping-

2010, 31(2):  198-205.  doi:10.11743/ogg20100210

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Based on the technique of 3D geological modeling and through analyzing the spatial distribution and mutual dessection of faults with interpreted seismic and drilling data,we have build a structural model for the lower unit of Paleogene Sha-3 Member in Block Wei-95,by which the structural features are recognized,including fault strike and spatial extension.The accuracy and reliability of basic data are crucial to 3D geological modeling,but Block Wei-95 is a typical complex fault-block reservoir,where the stratigraphic correlation is insignificant and the faults are difficult to be identified in many wells,resulting in a series of problems in basic geological studies.During this structural modeling,combining the special techniques of 3D modeling softwares with the basic geological study has played a significant role in several basic geological aspects such as the refined structure location and the refined stratigraphic correlation.Thus many problems that can not be solved by the conventional methods have been solved here,and the model precision has been guaranteed.

Three dimensional lithology modeling of volcanic reservoirs in the Changling gas field

CHEN Ke-Yong-

2010, 31(2):  206-211.  doi:10.11743/ogg20100211

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The lithologies of volcanic reservoirs in a single well in the Changling gas field are recognized by means of thin section analysis,core observation and description,FMI analysis and conventional well log analysis based on BP neural networks and discriminant analysis method.Three volcanic bodies are identified through 3-D seismic analysis,and the velocity of volcanics is achieved by establishing seismic velocity inversion model.A three dimensional lithology model for volcanic reservoirs is constructed by integrating the sequential indicator simulation and the Co-kriging method,and on the basis,laying down a sound foundation for further exploration and development in the gas field.

Prediction of sublayer sandstones based on wave impedance inversion in the wellblock of the horizontal well Zhou-57

DAN Jing-Fu, WANG Feng, SUN Hai-Lei, SUN Ji-Gang, HAN Xi-

2010, 31(2):  212-218.  doi:10.11743/ogg20100212

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During the whole process of petroleum exploration and development,the prediction of sandbodies in any target area,especially those in wellblocks of horizontal wells,is always dependent upon an analysis of reservoir deposition systems.The well Zhou-57 produces from the Putaohua Formation,which was deposited within the transition zone from a large-scale delta front to lake in northern Songliao Basin.The formation features in thin single sand bodies with a thickness of less than 2 m.The spatial distribution of these sandbodies is controlled by the variation and evolution of deposition systems during different geological times.The distribution and strike of sandboies are strictly controlled by lake transgression and regression.Therefore,a fine description of these sandbodies requires firstly a detailed geological study and then a prediction of sandstone sublayers through seismic wave impedance inversion.The prediction results can be used as important reference factors to adjust the injection-production pattern and improve the recovery ratio during the later phase of development.

Physical simulation of lithologic reservoirs in the Shengtuo area of the Dongying Depression

MOU Xue-Mei, ZHAO Wei-Wei, CHA Ming-

2010, 31(2):  219-224+231.  doi:10.11743/ogg20100213

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Sand lens and structuralˉlithologic reservoirs are the main types of lithologic reservoirs for growth of reserves and production in the Shengtuo area of the Dongying Depression. We conduct a physical simulation on its accumulation characteristics，and the results show that significant conditions which determine the forming of lithologic reservoirs are sufficient and effective gas sources，charging patterns，changes of physical properties of sand lens，and the relative positions of faults connecting reservoirs with source rocks to sand bodies. Among these conditions，faults connecting effective source rocks and reservoirs are critical to the forming of lithologic oil/gas reservoirs，and the changes of physical properties of sand bodies and the relative positions of faults to sand bodies are the main controlling factors of oil saturation. According to this study，the next exploration targets in this area should be the center of sand lens and the sand bodies in the upper wall of structuralˉlithologic oil/gas reservoirs.

Wavelet effect and recognition methods of thin sand bodies in braided river facies

HUANG Jun-Bin, GAO Li-Jun, GAO Yong, WANG De-Fa-

2010, 31(2):  225-231.  doi:10.11743/ogg20100214

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Under a fixed seismic frequency，wavelet side lobes may increase the difficulty of interpreting and recognizing thin sand bodies. To investigate the impacts of wavelet side lobe effects，we design a series of forward models and produce synthetic seismic profiles using zero phase Ricker wavelets of different frequencies. The purpose is to identify the relationship of sand body location and frequency with side lobe effects. This study also aims at exploring the relationship between amplitude attributes and the description of thin sand bodies. The results show that，an integrated use of multiˉfrequency profile and amplitude attributes can reliably interpret and describe thin sand bodies of braided river facies which are thicker than1/8wavelength.

Quantitative identification of waterˉflooded zones in conglomerate reservoirs —an example from the Kexia Formation in the Liuzhong block of Karamay oilfield

TAN Feng-Qi, LI Hong-Qi, WU Xin, FAN Xiao-Qin, YU Hong-Yan-

2010, 31(2):  232-239.  doi:10.11743/ogg20100215

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The conglomerate reservoirs inKaramay Oilfield have entered the development phase of high waterˉcut after forty years of water flooding. An accurate identification of waterˉflooded zones as well as a quantitative classification of wateringˉout level is the key and difficult issue to be considered in the adjustment of development strategy in this maturing oilfield. This paper documents a study that takes the conglomerate reservoirs in the Kexia Formation of the Liuzhong block as an example. It analyzes factors that affect the reservoir parameters by using the pressure coring data of three wells that were the focus of development adjustment in 2006 and by combining the actual geological characteristics of conglomerate reservoirs. It also selects logs that match well with the geoˉlogical characteristics and production pattern of the conglomerate reservoirs. Models for the interpretation of physical properties，lithology，water production rate，and water drive index of the Kexia Formation are established based on methods like cross plotting and multivariate linear regression. Three parameters，namely the water production rate，the oil saturation，and the water drive index，are chosen to be the main factors for aquantitative determination of wateringˉout level. Combining these factors with qualitative resistivityˉidentification chart for wateredˉout zones，the study offers rules and methods for qualitative identification of wateredˉout zones in this kind of reservoirs. The application of the method to the Kexia Formation yielded a coincidence rate of as high as 84.36%，well beyond the required accuracy. A set of technologies for quantitative identification of wateredˉout zones in conglomerate reservoirs is finally developed to improve the accuracy of wateredˉout zone identification.

A numerical simulation of volcanic gas reservoirs under consideration of start-up pressure gradient

XU Jin-Jin, XU Xu-Hui, FAN Zhe-Yuan, HU Jian-Guo, SONG Yan-Bo, GUO Ming-Li, WANG Shu-Ping

2010, 31(2):  240-243+259.  doi:10.11743/ogg20100216

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The Darcy flow theory suitble to conventional sandstone gas reservoirs with a single medium can not be applied to volcanic gas reservoirs,because they are characterized by the dual media of matrix and fracture and the higher original water saturation,resulting in an impact of star-up pressure gradient on a percolation process.According to the theory of mass conservation,a mathematical model of two-phase(gas and water) flow in dual media was built under consideration of start-up pressure gradient,for which the finite difference approch was used to obtain numerical solution and a calculation program of numerical simulation was compiled.In combination with laboratory experiment results,the values of this model parameters are determined,and it is shown that the impact of start-up pressure gradient has to be considered when permeability is lower than 0.1×10-3 μm2 and irreducible water saturation is over 20%.The numerical simulation results of a single well in XS gas field are consistent with the actual situation,and several indices of production and development,such as production plateau time,gas output during production plateau,recovery degree of production plateau and final recovery efficiency,are lower when the impact of start-up pressure gradient is considered than not.It is obvious that the impact of start-up pressure gradient has to be considered during the production of volcanic gas reservoirs.

An application of biharm onic spline interpolation to integration of logging and seism ic data

XIA Ji-Zhuang-

2010, 31(2):  244-249.  doi:10.11743/ogg20100217

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By employing Green，s function，the principle and pattern of biharmonic spline interpolation are studˉied，and the formulas of one tomultiple dimensional biharmonic spline interpolation are deduced.One feature of this algorithm is itsm inimal filter curvature.On a basis of applying the biharmonic spline interpolation，a converˉgence algorithm ofgrid node value is used to approximate the gridˉnode values to their surrounded values at logˉging structure data，and to make the separate logging structure data in every well impact and change adjacent seism ic structure data in a certain way，therefore resulting in an integration of logging and seism ic data. The effect of this biharmonic spline interpolation has been verified by its application in the typical complex reservoir in Yongˉ3faulted block，Shengli oilfield.The application results indicated that the structuralmaps proˉduced by thismethod on a basis of3D seism ic data with high precision can well avoid m istakes in the structural mapswith lower resolution produced by only using logging data，due to higher resolution of the formermaps.This method of biharmonic spline interpolation can effectively integrate seism ic data with logging data in predicting stratigraphicˉstructural surfaces，and elim inate the uncertainties resulter from using a single type of data，thus making the prediction more accurate and reliable.

Simulation of fracture param eters in the3 rd sand unit of the Paleogene Fuˉ2m ember in the Q iaohekou oilfield

LIU Xiao-Jun-

2010, 31(2):  250-254+259.  doi:10.11743/ogg20100218

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Fractures in lowˉpermeability reservoirs not only provide accumulation space and also act as seepage channels.However，present research on these fractures ismostly confined to qualitative descriptions.An accurate calculation of certain fracture parameters，such as openess，density，porosity and permeability，is of great imporˉtance in fracture quantitative descriptions and also a fundamental factor for the developmentofoil and gas fields.This paper documents a study that tries to construct a relationship between the ancient earth stress during the fracture form ing period and fracture parameters and that between the present earth stress and the parameters，determ ine the characters and directions of ancient earth stress through a structure analysis，and calculate the direction and strength of the present earth stress by using suchmeans as sonic velocity，hydrofrcturing，and sound em ission.The results are introduced into the fracture parameter calculatingmodel to simulate and calculate the openess，density，porosity and permeability of the fractures in the3 rd sand set of the Paleogene Fuˉ2member in the Qiaohekou oilfield.It is concluded that fractures are highly developed in the structural high near the main fault and the differences in fracture permeability reflect the differences of their directions.Core statistics and log interpretation verify the correctness of the stimulation results of the model.

A study on reservoir parameter changes after polymer injection in Block 1 of the central Gudao

HE Hu-Jun, WANG Qiu-Yu, CHENG Hui-Ming-

2010, 31(2):  255-259.  doi:10.11743/ogg20100219

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By using the core analysis data before polymer injection and after polymer breakthough from two wells in the polymer-injection area of Block 1,the central Gudao,the change patterns of reservoir parameters after a long-term polymer drive are compared and discussed.It is suggested that the long-term polymer drive has resulted in enlarging some small pore throats,improving the communication among pores and reducing pore tortuosity in the reservoirs.For the microscopic parameters of the reservoirs,the maximum,average,and normal pore-throat radiuses increased,the expulsion pressure,the mercury 50% saturation pressure and the variation coefficient decreased,and the mean coefficient rised.For the macroscopic reservoir parameters,the permeability was enhanced,and the porosity variation was within the range of allowable error.

A study on effectively improving waterflood development of oil reservoirs with high freezing point——an example from Shen25 block in the Damintun Sag,the Liaohe Basin

ZHOU Wei, TANG Zhong-Hua, WEN Jing, GONG Yao-Jin-

2010, 31(2):  260-264.  doi:10.11743/ogg20100220

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Oil with high freezing point is different in flowing properties at different temperatures,resulting in a series of difficulties in waterflood development of oilfields.To solve the problem,with experimental results and an integration of geological modeling and reservoir numerical simulation,we analyze the temperature field distribution in the reservoir at different surface temperatures of injected water.It is found that 60℃ is an important critical temperature.Over 60℃,the crude oil is a Newtonian fluid,with no wax crystallization and lower viscosity.The study results also show that the surface temperature of injected water at 80℃ is the best in waterflood development effects.Furthermore,the temperature field distribution among wells and its prediction were also analyzed,which provided guidance for the plan optimization of high freezing-point reservoirs in improving development and enhancing oil recovery.