Table of Content

08 December 2015, Volume 36 Issue 6

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Formation and preservation mechanism of sweet spot in tight clastic reservoirs —A case study of Chang 8 oil layer of Yanchang Formation in Zhenjing area, southwest Ordos Basin

Liu Chunyan

2015, 36(6):  873-879.  doi:10.11743/ogg20150601

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Densification of clastic reservoirs and difficulties in predicting their sweet spots constrain petroleum discovery in basins in central and western China.In order to investigate the mechanisms of reservoir densification and formation and preservation of sweet spots,a comprehensive study of sedimentology,petrology,and geochemstry were performed by using various methods,including core observation,microscopic observation of casting thin section and under fluorescence and cathode luminescence,fluid inclusion analysis,particle size analysis,mercury injection and permeability tests under overburden pressure,scanning electron microscopic analysis and so on.According to the generic types,sweet spots of the Chang 8 oil layer of Yanchang Formation in Zhenjing area, southwest Ordos Basin,are divided into a primary type and a secondary type.Early developments of chlorite films moderately inhibited later diagenesis processes,which is the main factor contributing to the formation and preservation of the primary sweet spot.The secondary type can be subdivided into a dissolution-type and a fracture-type according to their major pore space being dissolution pores or microfractures.The key factor determining the formation of the secondary sweet spot is constructive diagenesis.It can be concluded that the early charging of hydrocarbons effectively inhibited later cementation,and the multiphase diagenesis resulted the formation and preservation(or lost)of sweet spots.In vertical sections,individual sand body de-densification started from layers of relative high permeability,or areas of fracture and dissolution superimposing,and propagated outwards progressively.In planar view,sand body de-densification shows similar features,the sweet spots distribute in “bamboo-like” shape along the sand body.

Recognition of depositional environment of Cambrian source rocks in Tarim Basin

Chen Qianglu, Yang Xin, Chu Chenglin, Hu Guang, Shi Zheng, Jiang Haijian, Liu Wenhui

2015, 36(6):  880-887.  doi:10.11743/ogg20150602

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The Cambrian source rocks are considered as one of the most important source of marine oil and gas in Tarim Basin.Previous literatures documented various descriptions of their depositional settings,causing confusion in prediction of source rocks,especially those with no sufficient data.Analyses of outcrops,new drilling and seismic data,and assumptions of prototype basin from the Sinian to Cambrian,were used to study the sedimentary environment of the rocks through a perspective of sedimentary texture and hydrocarbon generating organisms to work out constraints over their distribution.The results show that the Cambrian sedimentary framework of Tarim basin can be characterized as “Western Platform and Eastern Basin”.It evolved through a carbonate ramp in the Early Cambrian and a feebly rimmed platform in the Middle-Late Cambrian.The source rocks of the Lower Cambrian were widely distributed in the middle-outer ramp.The Lower Cambrian Xishanbulake Fm source rocks in eastern Tarim Basin and the Lower Cambrian Yuertusi-Xiaoerbulake Formation in western Tarim Basin have the same bio-precursors assemblage which change from benthic algae of to planktonic algae,corresponding to the Early Cambrian progressive-retrogressive sedimentary succession.Regional sedimentary-tectonic evolution background and lithology and bio-precursors reveals that the Cambrian source rocks were developed in the deep shelf environment predominantly,and could be further divided into muddy source rocks and carbonate source rocks.The muddy source rocks were dominated by benthic algal,while the carbonate source rocks were dominated by planktonic algae.In vertical,the muddy source rocks and carbonate source rocks are superimposed on each other.

Main controlling factors of hydrocarbon accumulation in the Eastern Sub-basin,North Yellow Sea

Liu Jinping, Wang Gaiyun, Wang Liaoliang, Jian Xiaoling, Du Min, Wan Xiaoming

2015, 36(6):  888-896.  doi:10.11743/ogg20150603

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Eastern Sub-basin of the North Yellow Sea is still in the early stage of exploration,its petroleum geologic conditions are complex,and the main controlling factors of hydrocarbon accumulation are still not clear.Drilling data,petroleum geochemistry,organic phase classification,diagenesis and fluid inclusion thermometry were integrated to determine the main controlling factors of hydrocarbon accumulation.The distribution of source rocks with low to moderate abundance has controlled the area of oil and gas,and the hydrocarbons occur typically adjacent to the source rocks in vertical.But it is difficult for oil and gas to accumulate in the structural zone far away from the “hydrocarbon kitchen” and the main source rock intervals.The sedimentary process of slowly and shallow burial in early stage-intense uplift in middle stage-rapidly and deep burial in late stage affected the distribution of hydrocarbons.This special sedimentary-burial process also controlled the generation-expulsion history and the reservoir evolution history in the Eastern Sub-basin,and resulted in that the events of generation and expulsion and accumulation of hydrocarbon all occurred during the Neogene.Due to the influences of diagenesis and other factors,the major targets had been turned into the low-porosity and low-permeability reservoirs in the Neogene,making it hard for hydrocarbons to migrate in long distance.Therefore,large-scale hydrocarbon migration and accumulation have not occurred in the Eastern Sub-basin.As a whole,the reservoirs in Eastern Sub-basin features in near-source accumulation,so the targets adjacent to the main “hydrocarbon kitchen” have the lower risk of exploration.Therefore,the structural traps and structural-lithologic composite traps of the secondary structures,which are adjacent to “hydrocarbon kitchen” with good reservoirs,can be the favorable targets in the further exploration.

Characteristics, types and genetic mechanism of Baodao transfer zone, Qiongdongnan Basin

Tong Hengmao, Fan Caiwei, Tong Chuanxin, Song Peng, Zhang Hao

2015, 36(6):  897-905.  doi:10.11743/ogg20150604

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3D structure of Baodao transfer structure zone of the Qiongdongnan Basin was characterized by using structural interpretation and variance cube slices of 3D seismic data.This transfer structure features in “complex structure”,“multiple segments”,“multi-stage activities” and “Compound displacement transfer”.On this basis,it is proposed that more complicated transfer zone(compound transfer zones)exists in rift basin were proposed.Combining with the classic classification of transfer zone,a new classification scheme of transfer structure zones in rift basin was proposed.Furthermore,two genetic types of “pre-existing fabric activation type”(Baodao type) and “pre-existing fabric controlling type”(Morley type)were suggested.

Fault zone architecture of Xiahong North Fault zone in Junggar Basin and its sealing properties

Wu Kongyou, Li Siyuan, Pei Yangwen, Guo Wenjian, Liu Yin

2015, 36(6):  906-912.  doi:10.11743/ogg20150605

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A fault is not only a planar surface,but a 3D geologic body with complex internal structures some time,which can be divided into several units.Each unit has a different sealing mechanism,thus should be evaluated with different methods.Through integration of core observation with seismic interpretation,the Xiahong North Fault is divided into two segments,an east and a west segment,in plain view,two units,a slip fractured zone and a induced fracture zone,in sectional view.The slip fractured zone experienced strong compression,twisting and abration,resulting in strong cataclasis,thus can be quantitatively evaluated by the indices of ‘Fault Surface Stress',‘Shale Gouge Ratio' and ‘Fault Zone Filling'.The induced fracture zone experienced relatively weak cataclasis and had highly-developed fractures,better poroperm properties,thus can be analyzed according to diagenetic cementation and oil thickening by using thin section and SEM technologies.For the slip fractured zone of Xiahong North Fault,the west segment presents better sealing properties than the east segment,while for the fractured zone,the west segment is sealed by cementation and the east segment is filled by thickened oil.The SEM and fluid inclusion analyses suggest that there are at least three periods of fluid migration affecting the properties of the Xiahong North Fault,of which the 1^st fluid migration is dominated by formation water and the 2^nd-3^rd fluid migration is accompanied by hydrocarbon migration.Therefore,the sealing properties of the Xiahong North Fault zone are the result of the multiple fluid activities in geologic history.

Erosion thickness recovery and tectonic evolution characterization of southern East China Sea Shelf Basin

Li Deyong, Guo Taiyu, Jiang Xiaodian, Zhao Hanqing, Wang Haiping

2015, 36(6):  913-923.  doi:10.11743/ogg20150606

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Considering the fact that only a few exploratory wells in southern East China Sea Basin were drilled,we resorted to sufficient seismic data here to restore the critical unconformity erosion thickness and study the basin infilling and tectonic evolution by employing approaches including stratigraphic trends contrast,acoustic travel time,and sedimentary fluctuation analyses.The results show that the denudation of the basin was the most intensive during the Late Paleocene and Early Eocene,leading to the formation of the T₄⁰ unconformity with the largest erosion thickness of 800-1 000 m in the slope and uplift zones of Jiaojiang-Lishui Sag,and the least erosion thickness of 200-400 m in Fuzhou Sag as well as the medium erosion thickness of 200~600 m in Diaobei Sag.During the Late Oligocene and Early Miocene when the denudation was less intensive,the unconformity T₂⁰ was formed with mostly 500 to 600 m erosion thickness in the western slope of Diaobei Sag,the northern part of Fuzhou Sag,Yandang Low Bulge,and southern segment of the western slope of Jiaojiang-Lishui Sag.In the Paleocene,rifting and faulting activities initiated in the western depression,forming a dustpan-shaped “eastern faulted and western overlapping” structure;then shifted to east depression (leaving the west part to enter the stage of depression-inversion in the Eocene),forming a “bidirectional faulted” structure in Diaobei Sag.The Oligocene saw the east part also entered the depression-inversion stage but less intensive with the depression gradually turning into the westward overlapping dustpan structure.After the Miocene,the East China Sea Shelf Basin slowly entered the regional subsiding stage from west to east.

Structural deformation and genesis of the northern sub-basin in South Yellow Sea since Late Cretaceous

Gao Shunli, Xu Xi, Zhou Zuyi

2015, 36(6):  924-933.  doi:10.11743/ogg20150607

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South Yellow Sea Basin is one of the major petroliferous basins offshore China.It has been explored for years but with no significant commercial discovery due to a lack of understanding of its structure,diversified fault systems and complicated tectonic evolution.To evaluate the exploration potential and gain insight into faulting activities and sedimentation of the basin,we performed characterization of the tectonic deformation and formation mechanism analyses of the northern sub-basin in South Yellow Sea Basin since the Late Cretaceous based on a combination of the latest two-dimension seismic data with relevant geologic setting,drilling data and previous research papers.It shows that thrust faults were formed in the marine strata due to the compression and deformation the Indo-China period,and the fault system served as the basement faulting system since the Late Jurassic.It was later reactivated by extension and controlled the activities of faults within the basin as well as the sedimentary framework.A faulted depression cluster that was dominated by extensional structural deformation formed,reflecting a relationship of shallower strata being constrained by the deeper ones.

Geological and geochemical characteristics of silicified hydrothermal fluids in Well Shunnan 4,Tarim Basin

Li Yingtao, Ye Ning, Yuan Xiaoyu, Huang Qingyu, Su Bingrui, Zhou Ruiqi

2015, 36(6):  934-944.  doi:10.11743/ogg20150608

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Cores from the Ordovician Yingshan Formation limestone in the of Well Shunnan 4 of the Tarim Basin show remarkable signs of hydrothermal alteration and metasomatism of silicon.Dissolved fracture-cavity,loose siliceous limestone/siliceous rock,hydrothermal veins and large quartz crystal cluster were abnormally developed.Observation of geological characteristics of the samples and analyses of fluid inclusion/rare earth elements and trace element,all suggested a mixed origin of the thermal fluids.It is believed that igneous activities provided energy and volcanic thermal fluid together with formation water formed a mixture of low-to-medium temperature and high salinity silicified hydrothermal fluid.REE analyses reveal that δEu values range from 0.040 to 0.118 and average 0.069-negative anomaly that indicates a reductive environments; Sm/Nd ratios range between 0.169 and 0.256 and average 0.194,indicating a crustal diagenetic fluids.The high similarity between the average REE distribution curve of samples and those of earth's crust suggests the origin of heat from magma,and to be more specific,the upper crust as indicated by a lack of Mg²⁺ in the samples.Ba/Sr values range from 0.43 to 19.76 and average 6.70.Such a wide variation means the relative complexity of the fluid.U/Th ratios range from 0.35 to 4.76 and average 2.14.Th/U ratios range from 0.21 to 2.88 and average 1.03.And Th/U-Y/Ho correlations all indicate that the fluid is of low-temperature type.

Characterization of clay minerals in Toutunhe Formation of Fudong slope area in eastern Junggar Basin

Yu Jingwei, Zheng Rongcai, Liu Ni, Li Yun, Wen Huaguo

2015, 36(6):  945-954.  doi:10.11743/ogg20150609

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The Toutunhe Formation of the Middle Jurassic is the main exploration layer in Fudong slope area in Junggar Basin,where reservoirs are greatly influenced by sensitivity to clay minerals.Contents and types of clay minerals of the reservoirs are the major factors that influence sensitivity,thus were studied through cast thin section,rock thin section,X-ray diffraction and SEM.The result shows that ①various types of clay minerals can be observed and the thickness of clay membrane is related to some extent with productivity;②components of the clay minerals were determined by provenance,and sedimentary setting,climate change and later faulting helped transformation and preservation of the clay minerals;③abnormal pressure affects the distribution of the clay minerals;④the reservoirs are mostly water-sensitive and also acid-and speed-sensitive to some extent.The degree of sensitivity depends on the content of different types of clay minerals.The above understanding has been used as geologic basis for reservoir protection and modification during drilling,injection and production operation in the Formation.

Geochemical characteristics and origin of natural gas in the Xujiahe Formation in Yuanba-Tongnanba area of Sichuan Basin

Wu Xiaoqi, Liu Guangxiang, Liu Quanyou, Liu Jingdong, Luo Kaiping

2015, 36(6):  955-962,974.  doi:10.11743/ogg20150610

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In order to investigate the origin and figure out the source of natural gas in the Upper Triassic Xujiahe Formation in Yuanba-Tongnanba area of Sichuan Basin,the composition and stable carbon and hydrogen isotopes were used to analyze the geochemical characteristics of the natural gas.The study indicates that the natural gas in the Xujiahe Formation in the Yuanba-Tongnanba area is mainly composed of methane.It appears to be dry gas with a dryness coefficient generally higher than 0.97.The δ¹³C₁ and δ¹³C₂ values are in the range of -34.5‰~-29.3‰ and -35.4‰~-21.5‰,respectively.The δ¹³C_CO2 values are generally higher than -8‰,and the δD_CH4 values are in the range of -181‰~-144‰ without significant correlation with δ¹³C₁ values.The identification of gas origin and gas-source correlation indicate that the natural gas in the Xujiahe Formation is mainly coal-derived gas and sourced from the coal-measure source rocks in the Xujiahe Formation.The gas in the 1^st and 2^nd Members of the Xujiahe Formation in the Yuanba area and the Xujiahe Formation in the Tongnanba area contain a certain amount of secondary oil-cracking gas,which are mainly the product of the low-degree cracking of oil generated by the Wujiaping Fomation source rocks.Some gas samples from the Xujiahe Formation in the Yuanba-Tongnanba area display partial reversal of alkane carbon isotopic series,and the partial reversal of the gas from the 3^rd and 4^th Members in the Xujiahe Formation in the Yuanba area is resulted from the fact that they were generated by the Xujiahe Formation source rocks in the high-mature stage,while that from the 1^st and 2^nd Members in the Xujiahe Formation in the Yuanba area and from the Xujiahe Formation in the Tongnanba area are attributed to the mixing of a small amount of oil cracking gas and a large amount of high-mature coal-type dry gas.

Characterization of deep water sedimentary system in the Miocene of Block A in Lower Congo Basin

Wang Linlin, Wang Zhenqi, Xiao Peng

2015, 36(6):  963-974.  doi:10.11743/ogg20150611

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Sedimentary types in the Miocene of Lower Congo Basin is of dominantly deep water gravity flow.Analyses of drilling and logging data combined with study of high-resolution 3D seismic attributes reveal characteristics of the deep water sedimentary system and sequence of southwestern lower Congo Basin.About 7 third-order sequences can be recognized from the Miocene of Block A:massive transportation,water channels,levees,lobes,abandoned water channels,flood fans and deep sea mud under their respective sequence frameworks.Features and scales of gravity flow under these frameworks vary greatly:small-scale highly-bent gravity flow channels and levees were developed in the less intensive sedimentation of SQ1-SQ2 and SQ4-SQ5 and massive complex gravity flow channels,lobes and levees were developed during the large-scale deposition of SQ3 and SQ6-SQ7.An integrated development characterization of the units was performed to establish the sedimentary model in the area:the massive transportation occurring near continental slope,water channel-levee complexes and flood fans near provenance,and abundant water channels in highly-bent area and lobes at the end of water channels.The modal may provide guidance for further deep oil and gas exploration in the area.

Depositional characteristics and tectonic control on sedimentation of the 1^st Member of Shahejie Formation in Huanghua Depression,Bohai Bay Basin

Zhang Yaxiong, Dong Yanlei, Cheng Kenan, Guo Lei

2015, 36(6):  975-984.  doi:10.11743/ogg20150612

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Huahua Depression is one of the most important petroliferous depressions in Bohai Bay Basin.Based on core observation,lithology association,sedimentary structure,paleontology and seismic data,this paper studied the depositional characteristics of the 1^st Member of Shahejie Formation in Huanghua Depression.We divided the target formation into three 3^rd order sequences,namely Es¹⁽¹⁾,Es¹⁽²⁾ and Es¹⁽³⁾,and nine system tracts.The results show that five facies including braided river delta,meandering delta,nearshore subaqueous fan,gravity flow and lacustrine facies develop in the 1^st Member of Shahejie Formation.We also analyzed the depositional characteristics and the space distribution of each facies.The braided river delta facies distributes in Banqiao sag,Beitang sag and the southwest of Qikou sag.The meande-ring delta facies mainly develops in the south of Huanghua Depression and the southeast of Chengning Uplift.The nearshore subaqueous fan facies develops near the foot of the Cangxian Uplift with steep fault side.The gravity flow facies occurs in the deep lake of the Qibei sag.Tectonic evolution,steepness of fault and palaeomorphology are the main controlling factors on the clastic sedimentary system of the 1^st Member of Shahejie Formation.

Characteristics of lower-middle Jurassic sandstone reservoirs in Amu Darya Basin,Turkmenistan

Chang Hailiang, Zheng Rongcai, Wang Qiang

2015, 36(6):  985-993.  doi:10.11743/ogg20150613

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Analyses based on data of casting thin sections,SEM,porosity and permeability analysis,mercury injection test,vitrinite reflectance and acoustic emission test reveal that lithic sandstone with fine to medium grain sizes dominate the sandstone reservoirs in the Lower-Middle Jurassic in Amu Darya Basin.Their formation was controlled by various genesis processes including compaction,cementation,dissolution and fracturing,among which,the most predominant is the multi-stage cementation of carbonate,siliceous and clay minerals that filled up primary pores first and later secondary pores.Secondary pores formed by the dissolution of the unstable components such as feldspar,debris and calcite,contributed the most to the formation of the reservoirs.Reservoir space was composed of remanent intergranular pores,intergranular and intragranular dissolved pores,intercrystalline micropores and fractures,causing ultra-low porosity and permeability in reservoirs.The development of the reservoir was interfered by many factors: sedimentary microfacies determined the location of the reservoirs;sustained steady tectonic subsidence controlled the early and middle stages of diagenesis;compaction and cementation caused tight formations;pore fluid changes facilitated dissolution of unstable components and cements and formed secondary pores,and the precipitation of later kaolinite and illite;and facturing activities improved the permeability of the reservoirs.However,development of the reservoirs was confined to some extent.The reservoir may be grouped into three classes based on physical parameters and pore structures.Among them,classes I and II are poor in quality,assuming high development risk.

Fine characterization of ultra-deep reef-shoal reservoirs of ramp-type in Changxing Formation in Yuanba gas field,Sichuan Basin

Long Shengxiang, You Yuchun, Liu Guoping, Feng Qiong

2015, 36(6):  994-1000.  doi:10.11743/ogg20150614

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The burial depth of the Changxing Formation in Yuanba gas field,Sichuan Basin,is nearly 7 000 meters,the biological reef-shoals are small in scale and scattered in distribution,and the reservoirs are small in thickness and poor in poroperm characteristics and connectivity.In addition,the gas field has a complex gas-water contact,and high contents of hydrogen sulfide and carbon dioxide.All of these make the gas development in the study area very difficult.For effective development of the gas reservoir,a series of technologies has been innovatively integrated to finely characterize the reef-shoal reservoirs and their inter architecture.Firstly,the major factors controlling the development of favorable reservoirs are summarized and a reef-shoal development pattern is built based on study of stratigraphy,sedimentary facies,modern reef-shoal deposition and diagenesis.Secondly,under the guidance of the reef-shoal development pattern,logging interpretation and reservoir identification are performed and a forward geological model is established by integration of well-seismic data,and then the reservoir distribution is predicted through sensitive seismic attributes extraction and inversion.Thirdly,the distribution of reef-shoal reservoirs is characterized by integrating geological constraints with seismic techniques,such as profile identification,plane constraint,3D boundary delineation,and connectivity detection.Finally,the reservoir connectivity and the spatial distribution of favorable reservoirs are analyzed.Via this workflow,three structure models of reef-shoal reservoirs are established to support the production planning and well deployment in the Changxing Formation of Yuanba gas field.

Microscopic pore characteristics and the source-reservoir relationship of shale —A case study from the Wufeng and Longmaxi Formations in Southeast Sichuan Basin

Hu Zongquan, Du Wei, Peng Yongmin, Zhao Jianhua

2015, 36(6):  1001-1008.  doi:10.11743/ogg20150615

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Shale serves as both hydrocarbon source rock and reservoir of shale gas.The microscopic features of the Wufeng and Longmaxi Fms shale in Southeast Sichuan Basin such as organic matters,inorganic minerals and pores are described with the technology of Argon ion milling and scanning electron microscop.The organic matters and the pores are regarded as a source-reservoir system to analyze the relationship between their spatial distribution and temporal evolution.The research shows that organic pores are more important than inorganic mineral pores in respect of hosting shale gas,and migrated organic matters develop more pores than in-situ organic matters.Inorganic mineral pores play an important role in the formation of shale gas by hosting abundant migrated organic matters.With plentiful rigid mineral grains such as quartz,the Wufeng and Longmaxi Fms shales had a hard intergranular pore system of inorganic minerals with high porosity,big pores and good connectivity in hydrocarbon generation stage,which can preserve abundant migrated liquid organic matter(oil).The migrated organic matters were stored in intergranular pores among rigid grains and then evolved into solid organic matter with organic pores by exsolution of gaseous hydrocarbons,and the gas filled the organic pores.This is the most favorable source-reservoir matching relation for the generation and enrichment of shale gas.Most of the intraplatelet pores in clay mineral aggregates had been lost in the early diagenetic stage,while a small amount of organic matters with organic pores were preserved under the support of cements and fluid pressure between the platelets.Pyrite aggregates form intergranular and intercrystal pores,part of which can preserve organic matter and organic pores with smaller size,but their total amount is limited.

Physical simulation on seepage features of commingled production and right time of production conversion for gas wells

Tan Yuhan, Guo Jingzhe, Zheng Feng, Xu Weifeng

2015, 36(6):  1009-1015.  doi:10.11743/ogg20150616

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In order to increase single-well productivity and improve development economics of low porosity and low permeability gas reservoirs,many production wells adopt the way of commingled production.By laboratory physical experimental analysis,the development process of commingled production was simulated to study the influences of seepage features of gas reservoir under the combined action of formation pressure,permeability and the main controlling factors on the development effect,and also the timing of production conversion.The results suggest that when commingled production is adopted in gas reservoirs,the yield contribution rate of high pressure and high permeability layers is always higher than that of low pressure and low permeability layers;As for low pressure and high permeability layers,their yield contribution rate is higher than that of high pressure and low permeability layers in the initial phase of the experiment,and they turn from the primary gas pay zones to the secondary gas pay zones in the later phase;Along with the pressure at the conversion points going down,the degree of reserve recovery presents a decreasing trend among different times of production conversion;the effect of production conversion of low permeability layers is better than that of high permeability layers.This is still a new attempt to analyses the seepage features of commingled production through physical simulation experiment and the results provide a reference for making a reasonable development technology strategy for similar gas reservoirs.

New evaluation indicators of commingled production for ultra-low permeability reservoirs

Xu Qingyan, Jiang Wenwen, Lin Wei, Zhang Lei, Wei Linguo, Yang Zhengming

2015, 36(6):  1016-1021.  doi:10.11743/ogg20150617

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Considering the vertical heterogeneity characteristics of multilayer reservoirs and nonlinear seepage regularity for fluid flowing in the ultra-low permeability reservoirs,natural large-scale outcrop model and nonlinear seepage numerical simulation software were adopted to research the development effect of commingled production for ultra-low permeabi-lity reservoirs.Results show that total recovery percent is influenced by permeability ratio,average permeability,layer number and oil viscosity during commingled production.With the increase of permeability ratio,the total recovery percent decreases and the difference between the higher and the lower permeability layers becomes larger;And the higher the average permeability is,the higher total recovery percent is;the more the layer number is and the higher the oil viscosity is,the poorer the develoipment effect is during commingled production.On this basis,a new parameter called “quad-element synthetic influence factor” is proposed to evaluate the development boundary for the commingled production of multilayer reservoir.Analysis indicates that the total recovery percent is in a power function relationship with this new parameter,which could be used as an important indicator for development effect evaluation of ultra-low permeability multilayer reservoir.

Quantitative prediction of permeability tensor of fractured reservoirs

Liu Jingshou, Dai Junsheng, Zou Juan, Yang Haimeng, Wang Bifeng, Zhou Jubiao

2015, 36(6):  1022-1029.  doi:10.11743/ogg20150618

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Aiming at difficulties to quantitatively predict fracture permeability tensor,present fracture occurrence was predicted based on occurrence change of rock mechanical layers.Present liner density of fracture was predicted based on the facture surface energy theory and the rock strain energy theory of fracture mechanics.According to the results of present stress field numerical simulation,fracture opening was calculated in three direction extrusion stress state and then present facture parallel permeability was determined.By using present fracture attitudes,static and dynamic coordinate systems were unified into geodetic coordinate system,a quantitative prediction model of multi-group fracture permeability tensors was constructed,formula for calculating the principal value of permeability and main value direction were given,and permeability at different directions in unit body was predicted by adjusting the dynamic coordinate system rotation angle.Three parameters,the ratio of the maximum and minimum value of the permeability,heterogeneity coefficient of permeability and variation coefficient of permeability,were defined to quantitatively evaluate fracture permeability heterogeneity.Fu-2 Member fractured reservoir in the eastern flank of Tongcheng fault belt was taken as an example to predict fracture permeability tensor.

Generation and application of three-dimensional MPS training images based on shallow seismic data

Zhang Wenbiao, Duan Taizhong, Zheng Lei, Liu Zhiqiang, Xu Huaming, Zhao Lei

2015, 36(6):  1030-1037.  doi:10.11743/ogg20150619

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Multi-point geological statistics is one of the hot spots in current study,and the creation of training image is a key part determining the accuracy and reliability of reservoir simulation.Based on the shallow high frequency seismic data,the morphology and quantitative aspects of shallow channel deposits are studied and used as prototype models for further investigation of morphology and scale statistics of channel sand body-ies in deeper oil reservoiors.Quantitative three-dimensional training image is established on the basis of high-precision seismic inversion data.Training image grids are selected and Petrel is applied to analyze its impact on multi-point geological statistics.Results show that simulation is consistent with the well point data,and the spatial morphology and sizes of different channels are constrained by the quantitative characteristics of training image.Simulation results can best reveal the geometric characteristics and spatial confi-guration of sedimentary facies when the grid size of 3-D training image is consistent with the actual grid of simulation model.It provides a new method to create the training image,and may serve as a reference example for the simulation of other types of deep-water sedimentary facies.

Pre-drilling pore pressure prediction based on seismic data for exploratory well: Oilfield A in Iraq

Chen Xin, Wei Xiaodong, Li Yanjing, Xia Yaliang, Zhou Xiaoming, Wang Gan, Wang Xiaotian

2015, 36(6):  1038-1046.  doi:10.11743/ogg20150620

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Pore pressure prediction before drilling is of great significance for ensuring drilling safety,choosing reasonable drilling mud density,designing well configuration,reducing drilling cost and protecting reservoirs.The accuracy of pressure prediction usually is not sufficient for drilling requirement due to a lack of logging data and multi-interpretation of seismic data.This paper focuses on an oilfield A in southwest of Iraq.To tackle the problem of inadequate exploration well data of deep layers and complicated seismic responses,we combined seismic data with regional geology and shallow well logging data to study the mechanisms behind pressure.We found out that the study area was controlled by fluid charging caused by lateral tectonic extruding and deep faulting.An optimized method for pre-drilling pressure prediction was picked out and improvement on the precision of the pore pressure calculating parameters was achieved through overburden pressure prediction based on seismic-well-integration,seismic velocity analyses based on geological consistency,and variation rate of seismic velocity estimation.Pore pressure coefficient of exploratory well in deep Jurassic was predicted to range between 1.95 and 2.05.The prediction was verified by actual measurement with an error less than 3% only.