Table of Content

28 October 2011, Volume 32 Issue 5

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Hydrocarbon accumulation in the shallow reservoirs of the Bohai Bay Basin: a case study of the Huanghekou Sag

Wang Yingbin, Huang Lei, Wang Qiang, Zhang You

2011, 32(5):  637-641,650.  doi:10.11743/ogg20110501

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As one of the petroliferous sags of Bohai Bay Basin,Huanghekou sag is abundant in shallow faults resulted from neotectonic movement.An analysis of the factors controlling hydrocarbon accumulation in the sag based on the abundant exploration data shows that these shallow faults play a key role in controlling hydrocarbon accumulation in the shallow reservoirs.Through the study on the fault combinations and the reservoirs under their control,we recognized three types of fault combinations and the corresponding hydrocarbon accumulation models.Moreover,we also identified the primary exploration targets for these fault combinations.For the ‘X’-type fault combination,fault block reservoirs featuring in long hydrocarbon-bearing interval and large scale are the primary targets.For the ‘cabbage’-type fault combination,the core and inner fault blocks are the primary targets.For the ‘Y’-type fault combination,the structural high near the main fault usually are the primary targets.

Geochemical behaviors and genetic types of crude oil in tidal zone and shallow water area of Liaohe oilfield

Yang Weiwei, Liu Guangdi, Wang Yanshan, Gao Gang, Feng Yuan

2011, 32(5):  642-650.  doi:10.11743/ogg20110502

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Tidal zone and shallow water area of Liaohe oilfield are important regions for production replacement.The crude oil types in the study area includes normal oil,heavy oil and super-heavy oil,of which the later two are mostly distributed in th shallow layers and are related to biodegradation and oxidation.According to sedimentary environment,organic matter types and maturity,the crude oils are grouped into 4 types.Type Ⅰ is mature oil with relatively high content of gammacerane,low Pr/Ph and ‘V’ normal sterane,and occurs in the middle to shallow reservoirs of Bijialing and Yuehai oilfields;Type Ⅱ is high mature oil with low content of gammacerane and ‘L’ normal sterane,and occurs in the relatively deep third member of Shahejie Fm in Yuehai oilfield;Type Ⅲ features in high contents of tricyclic terpane,and gammacerane and ‘L’ normal sterane,and occurs in the 3rd member of Dongying Fm of Hainan-11 and Kuihua-16 oilfields on both sides of the hydrocarbon kitchen;Type Ⅳ is relatively low mature oil with low content of gammacerane but high Pr/Ph,and occurs in the Dong-ying Fm of Kuihuadao oilfield.The four genetic types of crude oil indicate that there are several favorable source rocks developed in the tidal zone and shallow water area of Liaohe oilfield,and the deep layer of Yuehai oilfield and the Dongying Fm of Kuihuadao oilfield still have great petroleum potential.

Characteristics of hydrocarbon inclusions and the timing of the hydrocarbon accumulation in the Lianglitage Fm in Tazhong26-24 wellblock

Xing Yongliang, Zhang Nai, Zhang Baoshou, Zhao Ruihua, Chen Yangui, Yang Xiaoguang

2011, 32(5):  651-658.  doi:10.11743/ogg20110503

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Carbonate reservoirs of the Ordovician Lianglitage Formation in Tazhong26-24 wellblock are abundant in hydrocarbon inclusions.Three stages of hydrocarbon inclusions,including Ⅰ,Ⅱ and Ⅲ,are identified in the study area through analyses of occurrence,growth relationship and characteristics of the hydrocarbon inclusions,as well as microthermometric analysis of hydrocarbon inclusions and their coexisting aqueous inclusions.The stage Ⅰ inclusions(Ⅰ:OL+OLG) are dominated by light brown and colorless liquid hydrocarbon inclusions which exhibit moderate yellow to yellowish-white fluorescence under the UV-light.The stage Ⅱ inclusions(Ⅱ:OLG+OG) are mainly colorless and extremely light brown oil & gas inclusions with strong blue white to blue fluorescence under the UV-light.The stage Ⅲ inclusions(Ⅲ:OLG+OG+OA)are mainly light brown,brown and deep brown oil & gas hydrocarbon inclusions which are characterized by strong yellow to tan-colored fluorescence under the UV-light.Moreover,they were formed within temperature ranges of 80~90℃,90~100℃ and 97~110℃ respectively.Finally,in combination with the geological background of the study area,we believe that there are three accumulation periods in the Lianglitage Formation of Tazhong26-24 wellblock:intermedium hydrocarbon accumulation in the Late Hercynian period,light oil-condensates accumulation in the Early Himalayan period and highly mature hydrocarbon accumulation in the Late Himalayan period.

Gas of biodegradation origin and their pooling characteristics in northern Songliao Basin

Shuai Yanhua, Song Na'na, Zhang Shuichang, Feng Zihui, Zhu Guangyou, Wang Xue, Huang Haiping

2011, 32(5):  659-670.  doi:10.11743/ogg20110504

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Songliao Basin has similar favorable geological conditions for biogenic gas accumulation as the Cretaceous basins in North America,including the both dimension and high quality of source rocks.At present,17 gas reservoirs in the Songliao Basin have been discovered to have the features biogenetic gas such as high dryness coefficient(C₁/ΣC₁₊>0.95)and light stable carbon isotope(δ¹³C₁ ranging from -60‰ to -50‰).Therefore,much attention has been paid to the biogenic gas potential in this area and study of their occurrence.Ho-wever,comprehensive analysis demonstrates that the discovered biogenic gas reservoirs are dominated by secondary biologic modification gas reservoirs with mixed secondary biogenic gas from biodegradation of thermal oil/gas and residual thermal gas.The following evidences were obtained from detailed geochemical character analysis:significant increase of isoparaffin content and significant decrease of propane due to biodegradation;biodegradation trace of stable carbon isotope ratios of heavy gaseous hydrocarbons;features reflecting biodegradation getting prominent along with the increasing N₂ content;significant biodegradation of liquid hydrocarbons associated with biogenetic gas reservoirs.Biodegradation degree,preservation conditions and the replenishment of thermal gas at later stage are the factors that complicate the characteristics of biodegradation gas.No primary biogenic gas reservoirs have been discovered so far.It is mainly caused by that the Songliao Basin has been in uplifting and cooling since the Late Cretaceous,unfavorable for the sustained generation and preservation of primary biogenic gas.Primary biogenic gas reservoirs possibly occur in lithologic traps in relatively stable blocks.Methods and marks for identification of secondary biogenic gas reservoirs are summarized to guide exploration of shallow biogenetic gases in other areas with similar background.

Comprehensive evaluation of regional seal in the middle of the first member of Shahejie Fm in the Qikou Sag

Shi Jijian, Fu Guang, Lü Yanfang, Li Lili, An Zhenyue, Zhu Na'na

2011, 32(5):  671-681.  doi:10.11743/ogg20110505

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Regional seal in middle of the first member of Shahejie Formation in Qikou Sag was comprehensively evaluated by using single well and gas reservoir data.The results show that the caprock was generally thick and continuous,and thus has relatively strong microscopic sealing ability.However,in the Beidagang buried hill structure belt and northern Banqiao depression,the reservoir pressure coefficient is relatively large and the displacement pressure of fault rock is relatively low due to the large vertical displacement of major faults in the caprock,being unfavorable for the preservation of gas.Based on four parameters including caprock thickness,displacement pressure,pressure coefficient of gas reservoir and vertical sealing ability of faults,a comprehensive evaluation method was proposed and used to evaluate the sealing ability of caprock in Qikou Sag.The results show that the caprock in most areas of Qikou Sag can seal gas reservoirs with medium to low reserves abundance and can seal gas reservoirs with high reserves abundance in central depression.

Secondary hydrocarbon generation of the Silurian asphalt sandstone in the Tarim Basin and its geological implication

He Kun, Mi Jingkui, Zhang Shuichang, Wang Xiaomei

2011, 32(5):  682-691.  doi:10.11743/ogg20110506

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This paper investigated the secondary hydrocarbon generation potential of the Silurian asphalt sandstone in Tarim through organic petrologic observation,geochemical analysis and simulated experiment of gold-tube pyrolysis.Observation on the organic petrologic features of asphalt sandstone samples from selected wells indicates that liquid oils also exist as another main type of organic matters in addition to solid asphalt.Analysis of total organic carbon(TOC)reveals that the Silurian asphalt sandstone with relative high value of TOC,which ranges from 0.56% to 3.46%.These studies suggest that the Silurian asphalt sandstone in Tarim Basin may have some potential of secondary hydrocarbon generation.Gold-tube pyrolysis experiments further confirm that the Silurian asphalt sandstone in Tarim can generate certain amount of hydrocarbons,mostly gaseous hydrocarbons,under intense thermal stress.The maximum gas yields of samples from Tazhong-11 well and Yuenan-1 well reach 46.80 mL/g and 41.11 mL/g respectively.Furthermore,comparative pyrolysis experiments on the original and chloroform-extracted samples reveal that the gas are mostly generated from cracking of the liquid oil in asphalt sandstone.Finally,geologic deduction is performed by using the kinetic parameters of HD-11 oil cracking.The results show that gas generation from secondary cracking is possible for the Silurian asphalt sandstone in certain zones in Tarim Basin under current burial depth.And those cracking gas may be an important sources for the gas reservoirs in the study area.

High-quality hydrocarbon source rock identification and hydrocarbon migration and accumulation characteristics in hte Wudong slope zone of the Hailer Basin

Wang Weiming, Lu Shuangfang, Cao Ruicheng, Shang Jiaohui, Chen Guohui

2011, 32(5):  692-697,709.  doi:10.11743/ogg20110507

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Based on high vertical resolution of well logging data,we used ΔlgR method to identify the high-quality hydrocarbon source rocks in Wudong slope zone of Hailer Basin and explored its relationship with hydrocarbon accumulation.Research showed that the high-quality hydrocarbon source rocks identified by logging in the vicinity of Wudong reservoir occur in stripped shape in the area from Wu 31 to Wu 108-112 wellblocks in Wu-dong slope zone.The crude oil in this area can be divided into two types.The first type of crude oil correlate well with the high quality source rocks in Wunan subsag in the downdip direction of Wudong reservoir,as they all show obvious characteristics of Ts>Tm and low gammacerane.The second type of crude oil correlate well with the high quality source rocks in Wudong slope zone as they all obviously featured in Ts

Characteristics of hydrocarbon pooling in Chang-10 interval of the Yanchang Fm in the northern Shaanxi province

Li Shixiang, Liu Xianyang, Han Tianyou, Huang Jinxiu, Jiao Jun

2011, 32(5):  698-709.  doi:10.11743/ogg20110508

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Oil-source correlation is performed in Chang-10 interval of the Yanchang Fm through comparative analysis of the geochemical characteristics of Chang-10 crude oil,Chang-7 and Chang 9 source rocks,as well as difference analysis of fluid inclusions homogenization temperature distribution between Chang-10 reservoir and other reservoirs with hydrocarbons from Chang 7 source rocks.Moreover,the factors controlling hydrocarbon pooling in Chang-10 are also identified based on sedimentary and reservoir characteristics.The result shows that the Chang-9 is the major source rocks for the Chang-10 oil reservoir,to which the Chang-7 also contributed limited hydrocarbons.The formation of the Chang-10 oil reservoir was controlled by various factors such as quality,deposition,diagenesis and micro-structure of source rocks.The distribution of the Chang-10 oil reservoir was controlled by the distribution and development of the Chang-9 source rocks.Favorable sedimentary facies belts,diagenetic facies zones and high overpressure zones of the Chang-9 dark mudstone are the favorable target areas for discovering oil reservoirs.The Chang-10 oil reservoir is controlled by both structure and lithology.Three main reservoir types are identified,including structural-lithological reservoir,up-dip pinch-out sandstone reservoir and up-dip tight layer sealing reservoir.

Formation mechanism and distribution of fractured buried hill reservoir in JZS oilfiled

Huang Baogang, Wang Libing, Zhao Chunming, Yang Qinghong, Cao Shuchun, Tong Kaijun, Song Hongliang

2011, 32(5):  710-717.  doi:10.11743/ogg20110509

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According to litho-chemical index and microscopic features,the buried hill in JZS oilfield can be divided vertically from top to bottom into three zones with different levels of chemical weathering:weathered,semi-weathered and un-weathered zones.Similarly,based on core observation,thin section analysis and image logging and in combination with production logging data,it also can be divided into three zones from surface to core:weathered crust,semi-weathered crust and basement,corresponding to the three chemical weathering levels respectively.The reservoir space of buried hill is dominated by structural fractures in semi-weathered crust and the solution fractures in weathered crust.The development of fracture reservoir is controlled by multiple factors such as lithology,tectonic movement,weathering and dissolution,of which tectonic movement is the main controlling factor.According to the timing of faults and their dip angle,the structural fractures of buried hill in JZS can be grouped into four types:early semi-filled/filled horizontal fracture,early semi-filled/filled vertical fracture,late semi-filled cataclastic fracture and late open slant fracture.By using crude oil inclusion detection technique,we recognized that the main effective fracture types of the buried hill in JZS are late semi-filled cataclastic fracture and late open slant fracture.We also established criteria for identifying effective fractures with conventional logging data calibrated by core and image logging data and restructured a new effective structure identification curve for fractured reservoir inversion and distribution prediction.Application shows that the prediction results of this method correlate well with that of other geophysical methods.This method provides the neccesary geological basis for development well emplacement.

Quantitative seismic interpretation of reservoirs based on the spectral decomposition technique

Bian Li'en, Yu Qian, Han Zijun, Chen Binbin

2011, 32(5):  718-723.  doi:10.11743/ogg20110510

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Spectral decomposition is a new technique for seismic reservoir research that transforms seismic data from time domain to frequency domain by discrete Fourier transform or maximum entropy approach.According to the theory of seismic wave propagation,this paper deduces the amplitude spectrum expression of thin beds and confirms their notches characteristics of spectrum,i.e.the reciprocal of notches period equals to the temporal thickness of thin bed.With this principle,we discuss ideas and methods of estimating reservoir thickness based on spectral decomposition.In practice,quantitative interpretation of reservoir thickness is realized by establishing a precise velocity field of targets and computing the first spectral peak frequency in target tuning cube.The application shows that the prediction results are consistent with the drilling data,indicating they are credible.Spectral decomposition provides a new approach and method for quantitative seismic interpretation of reservoirs and has broad application prospects.

Sequence stratigraphic models and reservoir prediction of the Paleozoic marine carbonates in the Lower Yangtze area

Ji Youliang, Zhou Yong, Wang Gaiwei, Lu Linlin

2011, 32(5):  724-732,786.  doi:10.11743/ogg20110511

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According to the principles of sequence stratigraphy and sedimentology,we studied the Paleozoic marine deposits in the Lower Yangtze area by using outcrop observation data integrated with drilling and logging data.We identified four types of unconformities through field observation,including uplifting-erosion unconformity,transgressive onlapping unconformity,underwater erosional unconformity and subareal erosional unconformity.In addition,we also identified 4 types of condensed sections,including the Sinian coal layer,the Silurian-Carboniferous Gaolishan Formation shale,thin Ordovician dolomite and thin Carboniferous limestone.According to these boundary marks,11 second-order sequences were recognized and a sequence stratigraphic framework was established in the Lower Yangtze area.According to the lithologies,facies and sedimentary structures defined through field outcrop observation,we established three sedimentary systems for the Paleozoic in the study area, namely continental sedimentary system,transition sedimentary system and ocean sedimentary system.Finally,based on the regional tectonic setting and previous research results,we studied the nature and evolution of basin in the study area.Three sequence stratigraphic models were established,i.e. the Sinian-Late Ordovician,Devonian and Carboniferous stratigraphy model of craton basin,the latest Ordovician-Late Silurian stratigraphy model of foreland basin and the Middle and Late Ordovician,Late Permian-Middle Triassic stratigraphy model of passive margin basin.Their sequence characteristics were summarized.

Identification of the shelf margin delta in sequence stratigraphic frameworks and its significance: a case study of the Baiyun Sag,South China Sea

Xu Qiang, Wang Yingmin, Lü Ming, Wang Dan, Li Dong, Wang Yongfeng

2011, 32(5):  733-742.  doi:10.11743/ogg20110512

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Shelf margin delta is characterized by high-quality combination of source rocks,reservoirs and caps,and multiple trap types.Based on genetic styles,it can be classified into three types:provenance-dominated type,sea level-dominated type and hybrid type.During the relative quiescence period of sea-level,large amount of sediments are transported to the continental slope by rivers,making the shelf break gradually move seaward.Then shelf margin delta deposits could be formed at the shelf break and continental slope.Moreover,during period with relative stable sediment supply,the lowering of sea level to the shelf break also can transport large amount of sediments crossing broad continental shelf to shelf break,forming shelf margin delta deposits.These characteristics make shelf margin delta system identifiable in sequence stratigraphic framework.For example,shelf margin delta often shows large 'S' progradational reflection structure on seismic profiles,and the thickness between top surface and bottom surface can reaches up to hundreds of meters,much thicker than that within continental shelf.Moreover,the shelf margin delta usually occurs in lowstand system tract and is characterized by landward and seaward slope wedges.Based on integrated analysis of recent well logs and high-resolution 3D seismic data from Baiyun sag,a series of Oligocene-Miocene shelf margin deltas were identified in the Zhuhai Formation and Zhujiang Formation,and some unique deep-water reservoir systems were also recognized in the shelf break.These understandings will be helpful to future deep-water exploration.

Sedimentary characteristics of slump turbidite fans in the upper third member of the Hetaoyuan Formation in the Biyang Depression

Liu Jianfeng, Zhu Xiaomin, Wang Min, Lin Sheqing, Xiong Chao, Liu Peng, Cheng Wenju

2011, 32(5):  743-750,791.  doi:10.11743/ogg20110513

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Analyses of lithology assemblage, grain size and seismic reflection characteristics of the upper third member of Hetaoyuan Formation reveal that the provenance of slump turbidite fan in the deep lake came from Houzhuang braided river delta in the northeast. The slump turbidite fans are characterized by grey medium-fine sized sandstones, interbedding with dark grey lacustrine mudstone in sharp contact, coexistence of lens and progradation reflection on the seismic profile, as well as low slope and one segment of grain-size probability curve. The drop of lake level was favorable for the formation of slump turbidite fan in delta front without external triggering mechanism. As water in northeast delta front was shallow, when the lake level dropped, part of the delta front exposed and lost stability due to the lost of buoyancy, resulting in local slumping. Wave action could strongly corrode and modify delta front sediments near the wave base and resulted in the formation of turbidite sandbody due to wave back flow. All the slump turbidite fans were developed in the lake mudstones between braised river delta and nearshore subaqueous fan. When the delta pushed forward rapidly and the lobes protruded long forward, it was easy to form slump turbidite fans large in both number and area. The number of slump turbidite fans increases and their area enlarges near the delta lobes.

Seismic responses and geological characteristics of mass-transport deposits in the Rakhine Basin,Offshore Myanmar

Ma Hongxia, Lü Fuliang, Fan Guozhang, Sun Hui, Gao Cuixin

2011, 32(5):  751-759.  doi:10.11743/ogg20110514

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Mass-transport deposits(MTD)are an important component of deepwater deposition system.They occur in many deepwater basins around the word and play an important role in petroleum exploration and production.Using deepwater 3D seismic data,we predicted mass-transport deposits in the lower of the Upper Pliocene in Rakhine Sub-Basin,offshore Myanmar.Based on the seismic sections and time slices,we recognized 3 seismic facies in the MTD:low amplitude,semitransparent and chaotic seismic reflections,imbricate variable amplitude reflections and moderate-high amplitude reflections.The first seismic facies is the typical seismic response of laminar flow in the middle MTD,the second seismic facies is the evidence of the syndepositional deformation at the toe of MTD,and the third seismic facies is the seismic response of the floating blocks in the MTD.Based on RMS,coherence slices and structure maps,we analyzed the typical geologic features on the top boundary,bottom boundary and in the interior of MTD.The bottom boundary is mainly characterized by erosion,and the top boundary reveals the laminar flow and plastic flow regimes of MTD,while the interior mainly features in deformation and compression.

Reconstruction of the Late Ordovician palaeogeomorphology and reservoir prediction in Yanchang exploration area,the Ordos Basin

Han Minqiang, Pu Renhai, Liu Haijuan, Guo Xiangdong, Liu Baoping

2011, 32(5):  760-767.  doi:10.11743/ogg20110515

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Major breakthroughs have been achieved in gas exploration in the Ordovician Majiagou Formation in Yanchang exploration area.These discoveries show that the development and distribution of gas-bearing layers have a close relationship with the furrow erosion palaeogeomorphology on top of the Ordovician.By using such techniques such as fine subdivision and correlation of the Majiagou Formation,thickness mapping of the Benxi Formation on the unconformity,forward modeling-based identification of eroded furrows on seismic section,and seismic inversion,we mapped the paleogeology of the pre-Upper Paleozoic and recognized two NW-SE trending eroded furrows on top of the Ordovician.The comprehensive analysis of the paleogeomorphogloic map and wave impedance map shows that the distribution of favorable reservoirs with low wave impedance in the Ordovician is consistent with the locations of erosion furrows and the eroded slopes on both sides.Moreover,it is also consistent with the locations of wells that produce gas from the Ordovician and that have favorable oil/gas shows.The research indicates that favorable reservoirs occur near Y112 well in Ganquan area,Y113-Y101 wells in the northwest of the study area and Y118-Y119-Y108 wells in central of the study area.These areas should be the major target areas for further exploration of the Ordovieian.

Structural features of post-salt layers in the middle sedimentary cover of Kuqa Depression,the Tarim Basin

Xie Huiwen, Li Yong, Guo Weixing, Wu Chao, Xu Zhenping, Qi Jiafu

2011, 32(5):  768-776.  doi:10.11743/ogg20110516

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The thick salt layer of Kumgeliem Group(E_1-2km)at the bottom of Cenozoic led to the complicated deformation of post-salt layers in Kuqa Depression.Structural deformation in the study area is studied based on interpretation of seismic data.The types of structural deformation were identified,i.e. contractional structure and salt diapir-related structure.The contrational structures can be divided into thin-skinned folds and thrusts,with salt layer as the detachment.The salt diapir-related structures can be divided into blind piercing diapir structure and piercing diapir structure,which were caused by local thickening and piercing due to salt along-bed flow.The salt diapire-related structures started to develop during the deposition of Jidik Formation(N₁j)and experienced two evolution stages.The first stage was the Miocene when salt diapir-related was mainly caused by the differential pressure of the overlying strata, while the second stage was the Pliocene and Quaternary when salt diapir-related diaper was mainly caused by horizontal depression.The contractional structures were mainly formed during the deposition of Kuqa Formation(N₂k)and Xiyu Formation(Q₁x),with deformation of decollement folds and development of thrusts on the limbs of folds.

Structural properties and interpretation methods of the Tazhong Low Salient

Guan Shuwei, Yang Haijun, Han Jianfa, Li Benliang, Luo Chunshu

2011, 32(5):  777-786.  doi:10.11743/ogg20110517

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Tazhong low salient is part of the foreland thrusting system in the southeastern Tarim Basin from Middle Ordovician to early Late Devonian.During this geologic period,the faults in Tazhong area were dominated by north-dipping and thrusts,and might intersected the deep north-thrusting major fault,forming a north-propagating wedge structure front.The low salient in Tazhong area experienced multistage tectonic movements,resulting in different structural geometries in different stratigraphic units.For example,NW-trending compressional fault-related folds dominate the Sinian-Ordovician structural layer;NE-trending negative flow structures and pull-apart grabens are predominant in the Silurian-Devonian structural layer;while positive flow structures and collapse structures resulted from magma invasion or diaper are prevalent in the Carboniferous-Permian structural layer.The early structures are commonly destroyed by the later structures duo to multistage faulting,making it difficult to identifying them on seismic section.Therefore,structure interpretation should be based on the seismic profiles with approximate the same vertical and horizontal scales,so as to correctly define the deformation features in these structural layers and extrapolate into areas where seismic data quality is low.

A new method of productivity prediction for high CO₂-content gas wells

Yan Jin, Liu Chuanxi

2011, 32(5):  787-791.  doi:10.11743/ogg20110518

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Productivity of gas wells in Songnan volcanic gas reservoir is difficult to predict as high CO₂ content has great influences on PVT of natural gas,resulting in large difference between the measured and predicted productivity.Based on laboratory experiments,this paper studied the effects of temperature,pressure and CO₂ content on PVT of gas with high CO₂ content and established the relational expressions of gas viscosity and Z-facto to pressure for gas with different CO₂ contents.A new prediction model considering PVT variations of gas with high CO₂ content was built based on gas percolation theory.The case study results indicate that the productivity reduces with the CO₂ content increasing;the effect of μZ factor changes on productivity prediction should be considered when CO₂ content is above 20%;and the impacts of CO₂ content on productivity lowers to a level that can be neglect in late production period.The new method is accurate and practical for the high CO₂-content gas reservoirs.

Reconstruction of microscopic pore structure in low permeability gas reservoirs by micro-CT scanning: an example from the Upper Shaximiao Formation in Xinchang gas field

Su Na, Duan Yonggang, Yu Chunsheng

2011, 32(5):  792-796.  doi:10.11743/ogg20110519

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In order to enhance gas recovery,it is necessary to construct pore network model and quantitatively describe micro-pore-scale percolation mechanism based on micro-pore structure.Taking cores of the Upper Sha-ximiao Formation in the Xinchang gas field of western Sichuan Basin as an example,this paper studies 3D reconstruction of pore structure.First,using micro-CT to scan core to get projection data,and using the FDK algorithm for construction of grayscale images.Then based on experimental porosity,using 2-value segmentation to cut grayscale images and using ray tracing algorithm to get 3D pore structure image(digital core).Statistical analysis of the properties of digital core shows that the porosity of digital core is almost identical to the measured core porosity with a relative error of only 0.1,which is in coincide with the properties of Upper Shaximiao Formation in the Xinchang gas field.It shows that reconstruction of micro pore structure with micro-CT scanning is feasible.The study provides a solid foundation for pore network modeling and subsequent microscopic flow simulation study.

Feasibility study and application of development seismic inversion-a case study from northern Changyuan oilfield of Daqing area

Li Zhandong, Zhao Wei, Li Yang, Peng Zheng, Zhang Haixiang

2011, 32(5):  797-806.  doi:10.11743/ogg20110520

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In order to make development seismic inversion and fine reservoir description feasible,we proposed a curve reconstruction method based on frequency division compensation.As logs with different frequency can reflect features of different sandstones,we reconstructed "quasi-wave impedance" curves through high frequency restoration and low frequency compensation.Inversion feasibility analysis experiments showed that result stability could be optimized and reservoir prediction accuracy could be improved through introducing curve reconstruction inversion,simulated annealing algorithm and high well-dense inversion.Meanwhile,forward modeling and inversion proved that 2 meters thin sandstone layer interbeded in thick mudstone could be recognized through development seismic inversion.But for sandstone layers with thickness less than 2 meters,they can be recognized only when interbeded within mudstone layers greater than 2 meters thick.Well-tied seismic sedimentary facies study was also carried out to refine prediction of sandbody volume on sides of channel,channel sand connectivity,channel sand scale change,channel combination and timing of channels.Large distributary channel sandbodies are high in oil potential and remaining oil is commonly caused by imperfect injection-production well pattern.Small distributary channel sandbodies locally have high oil potential,and remaining oil is commonly caused by limited control area of well patterns.