Table of Content

08 February 2015, Volume 36 Issue 1

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Breakthrough of Fuling shale gas exploration and development and its inspiration

Wang Zhigang

2015, 36(1):  1-6.  doi:10.11743/ogg20150101

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China marine shale gas field is characterized by wide distribution and richness in resources.But compared with North America, because of suffering multi-stages tectonic reworking, China marine shale is older and more mature, as a result, it is unique in preservation condition and buried depth.Based on these features, the theory of ‘three-element enrichment’, whose cores include the conditions of hydrocarbon generation, reservoir conditions and shale gas preservation conditions, is put forward.On this basis, shale gas exploration is focused on Sichuan Basin and its peripheral regions, and the Lower Silurian of Southeast region of Sichuan Basin is chosen to be the preferred breakthrough field for shale gas exploration by China Petroleum & Chemical Corporation.Shale gas zone and the target evaluation method is set up, and Jiaoshiba Block of Fuling is as the target area.And in 2012, well Jiaoye 1 was drilled, and discovered the first large shale gas field in China, i.e.marine shale gas field of Longmaxi Formation in Jiaoshiba Block.Drilling technologies and multi-stage fracturing technologies were developed for the marine shale with shallow to moderate burial depths.The rapid and highly efficient development of the Jiaohsiba shale gas field was realized through effective management under the guidance of integrated exploration and development.

Differential characteristics of cap rocks of volcanic gas reservoirs in the Xujiaweizi fault-depression, Songliao Basin

Zhang Lei, Zhu Lunwei, Lu Shuangfang, Zhang Xuejuan, Shen Jianian, Wang Yachun

2015, 36(1):  7-16.  doi:10.11743/ogg20150102

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Through analyzing the lithology, physical properties and spatial locations of the rocks overlying volcanic gas reservoirs, this paper investigated the types of cap rock and identification marks of each type in the Yingchen Formation of Xujiaweizi fault-Depression, and then discussed the spatial distribution, sealing ability and control on the formation of gas reservoirs of each cap rock type.The results showed that there were three types cap rocks of volcanic gas reservoirs in the Yingchen Formation of Xujiaweizi fault-Depression:typeⅠis mudstone cap rock overlying just on the top of volcanic gas reservoirs;type Ⅱ is compact volcanic cap rock located at the top of volcanic reservoirs; and type Ⅲ is compact volcanic cap rock interbedded with loose volcanic rocks in the upper section of volcanic reservoirs.Type Ⅱ and type Ⅲ cap rocks are mainly consisted of volcanic lava and pyroclastic rock.Both type Ⅱ and type Ⅲ cap rocks show high gamma-ray deflections and high density.The main difference between these two types of cap rocks is spatial distribution.The type Ⅱ cap rock is located at the top of volcanic reservoirs, while the type Ⅲ cap rock is located at the upper part of volcanic reservoirs and usually covered by volcanic rocks with low density.The type Ⅱ cap rock had the widest distribution area and best spatial continuity than the others.The displacement pressures of type Ⅱ cap rock was up to 8.8 MPa and single well daily gas production in reservoirs with this type of cap rocks is the highest (up to 36.6×10⁴ m³) in comparison with the other two types of cap rocks with the same thickness.The type Ⅰ cap rock has a smaller distribution area than type Ⅱ and it is mainly distributed in the edge regions of fault-depression.Its displacement pressures is up to 6.9 MPa and the highest single well daily gas production in areas with this type of cap rocks could reach 23.2×10⁴ m³.The spatial continuity of type Ⅲ cap rock was poor and its displacement pressures was usually under 4.75 MPa, resulting in the highest daily gas production of one we Ⅱ only of 12.8×10⁴ m³ in the distribution area of type Ⅲ cap rock.Comprehensive analysis showed that type Ⅱ cap rock had the best sealing ability among all cap rock types, sealing ability of type Ⅲ cap rock was the worst, and that of type Ⅱ cap rock was moderate.This difference of sealing ability among three types of cap rocks controlled the formation and enrichment of volcanic gas reservoirs.

Dating of hydrocarbon accumulation by fluid inclusion characteristics in the Chang9 of Yanchang Formation in Jiyuan area, the Ordos Basin

Shi Baohong, Zhang Yan, Zhang lei, HuangJing, Tang Chao

2015, 36(1):  17-22.  doi:10.11743/ogg20150103

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Chang9 oil layer of the Triassic Yanchang Formation is a key horizon for reservoir development in Jiyuan area, Ordos Basin.The characteristics of fluid inclusions in Chang9 reservoir in Jiyuan area were analyzed systematically based on the measurements of Fourier transform infrared spectroscopy, fluorescence spectroscopy, and homogenization temperature to determine, in combination with the burial-thermal history, the phases and periods of hydrocarbon migration and accumulation.The results show that there are two types of hydrocarbon inclusions in the reservoir of Chang9, namely liquid hydrocarbon inclusions and gas liquid hydrocarbon inclusions with green or yellow-green fluorescence.The homogenization temperature of brine inclusions associated with the hydrocarbon inclusions has a continuous distribution with a 100-120 ℃ peak value.Salinity distribution is relatively concentrated with a peak value of 3-5 wt%NaCl.These cha-racteristics indicate that there is one major phase of oil migration and accumulation in the study area.Consistently, fluorescence spectroscopy and Fourier transform infrared spectroscopy data demonstrate that the Chang9 reservoir has undergone one phase of hydrocarbon charging with high organic matter maturity, with yellow-green and green fluorescence, corresponding to the fluorescence spectrum of 495nm.The analysis of burial and thermo-evolutionary history of Chang9 oil layer show that the hydrocarbon charging occurred mainly in mid-late stage of the Early Cretaceous.

Accumulation conditions of tight sand gas in the 3^rd member of the Shahejie Formation in Nanpu Sag, Bohai Bay Basin

Guo Jigang, Dong Yuexia, Pang Xiongqi, Huang Hongxiang, Jiang Fujie, Xu Jing, Wang Pengwei, Peng Weilong

2015, 36(1):  23-34.  doi:10.11743/ogg20150104

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Based on analyses of the source rocks and reservoirs in the Es³ (the 3^rd member of Shahejie Fm), the hydrocarbon expulsion history was restored with the hydrocarbon generation potential method, and evolution history of reservoir porosity was established through numerical modeling.The results show that accumulation conditions of tight sand gas in the Es³ in the Nanpu Sag of the Bohai Bay Basin are pretty good: fair-good source rocks and widespread reservoirs were closely connected with each other, and the timing of gas accumulation and reservoir tightening was favorable.The peak gas expulsion occurred from the Guantao to early Minghuazhen, while the reservoir tightening was from the late Guantao to early Minghuazhen.These gases might accumulate in the lenticular sand body near the source rocks under the force of gas expansion, forming continuous tight sand gas reservoirs.

Reconstruction of geothermal history in Hulunhu Depression, Hailaer Basin

Cui Junping, Ren Zhanli, Li Jinxiang, Yin Lingling, Wang Wenqing

2015, 36(1):  35-42.  doi:10.11743/ogg20150105

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The Hulunhu Depression with thick deposits and well-developed strata is an important replacement exploration area in the Hailaer Basin.The Nantun Formation is its primary hydrocarbon source rock and the Tongbomiao and Damoguaihe Fms are the secondary source rocks.These source rocks have supreme oil-generating conditions, but no systematic study has been performed on its geothermal evolutionary history so far.The present geothermal gradient is 30.7 ℃/km in the Hulunhu Depression, belonging to the moderate temperature field.The average paleogeothermal gradient recovered by the vitrinite reflectance, homogenization temperature of fluid inclusions and apatite fission track method is about 42-56 ℃/km, obviously higher than the present geothermal gradient.That is to say, the paleogeotemperature is higher than the present geotemperature.The paleogeotemperature reconstruction and geothermal history simulation showed that the Hulunhu Depression reached the maximum paleogeotemperature in the Late Yimin period(90Ma), and entered a cooling process since the Paleogene and Neogene.The maturity of the Lower Cretaceous hydrocarbon source rocks was mainly controlled by the paleogeothermal field.The results from the studies of the paleogeothermal evolutionary history and the authigenic illite dating of reservoirs showed that the Late Yimin period was a very important stage for hydrocarbon accumulation in the Hulunhu Depression.In this period, the depression uplifted and got denudated, the temperature of strata reduced, the burial depth of source rocks decreased, and the intensity of hydrocarbon generation weakened.

Control of faults on hydrocarbon accumulation of buried hill reservoirs in the Nanpu Sag, Bohai Bay Basin

Liu Chang, Chen Dongxia, Dong Yuexia, Liu Guoyong, Zhang Hongchen, Ren Miaosong, Bao Yingjun

2015, 36(1):  43-50.  doi:10.11743/ogg20150106

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Buried hill reservoir of fault-block type is one of the important reservoirs in Bohai Bay Basin and its formation is significantly controlled by faults.In order to study the control of faults on hydrocarbon accumulation and preservation in buried hills of fault-block type, various data including 3D seismic, drilling and logging data were integrated to describe the geometry of fault planes, calculate the sealing capacity of faults, and analyze the control of fault on reservoir modification.The focus of analysis was put on the control of five major faults on the dominant pathways of hydrocarbon migration, preservation of accumulated hydrocarbons and the reservoir space for hydrocarbons.The following understandings were obtained:(1)The migration of hydrocarbons was controlled by the geometry of fault plane, carrier systems of convergence type were favorable for migration of hydrocarbons, and the section with heavy curvature could obtain high yield;(2)The sealing properties of faults after the hydrocarbons accumulation controlled the preservation of accumulated hydrocarbons and current oil-gas potentials.When the fault opening index (FOI) of faults on top of buried hills is less than 1, the vertical sealing capacity of the faults is good, the sealing conditions are good and the oil potential is high in later stage.When it is over 3, the vertical sealing capacity is poor and hydrocarbons migrate upwards to the shallow parts.(3)The modification of buried hill reservoirs by faults is reflected by the differential distribution of fractures.There is a negative correlation between the fractures density and the distance to the second-grade faults.To some extent, there is a positive correlation between production capacity and the fracture density.

Characteristics and origins of structural deformation in the Paleogene in the Western Sag of Liaohe Depression, Bohai Bay Basin

Yu Fusheng, Dong Yuexia, Tong Hengmao, Xiong Lianqiao, Long Xian

2015, 36(1):  51-60.  doi:10.11743/ogg20150107

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Research on structural evolution and dynamic processes in the Western Sag of Liaohe Depression is significant to not only oil and gas exploration, but also analysis of the evolution of Bohai Bay Basin and Tanlu Fault.According to seismic interpretation, analysis of the relationship between fault system, deposition thickness and the characteristics of fault intensity, it was concluded that the Western Sag of Liaohe Depression underwent two-phase deformation superimposition in the Paleogene.The early Eocene extensional phase including an initial fault depression stage (Es⁴) and a strong fault depression stage (Es³) resulted in the NE-SW-trending major normal faults and half-graben filled by the fourth and the third member of Shahejie Formation.The later Oligocene strike-slip phase during Dongying Formation caused the right-lateral strike-slip of the pre-existed basement faults and the formation of new normal fault arrays in NEE-SWW orientation.A structure style with transtension subsidence in the south part and transpression erosion in the north part formed during this stages owing to strike-slip displacement.The transition from extensional deformation to strike-slip deformation occurred during Es^1-2.Regional field analyses and sand box simulation results show that the Eocene extensional fault system was controlled by back-arc extension stress, which was triggered by subduction roll-back of the oceanic Pacific Plate from the Asian Continent.And the Oligocene strike-slip fault system was controlled by dextral displacement of Tanlu Fault, caused by the collision of Indian-Australian Plate with the Eurasian Plate.

Sedimentary record and origin of high frequency cycles in the Paleogene Kongdian Formation in the Jiyang Depression

Tan Xianfeng, Jiang Yanxia, Li Jie, Xue Weiwei, Li Zemin

2015, 36(1):  61-72.  doi:10.11743/ogg20150108

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There is a set of high frequency cycles with lithological combination of purple red mudstone, grey siltstone and gypsiferous mudstone developing in the Kongdian Formation of Jiyang Depression.By using logging data, well logging, core observation and elemental geochemistry methods, this paper researched the deposition mechanism of high frequency cycles of the Kongdian Formation in Jiyang Depression.The research results show that the cyclic sedimentation record of Kongdian Formation in Jiyang Depression consist of color meter scale cycle, graded meter scale cycle, non-graded meter scale cycle and consist of 6 types of lithofacies assemblages which include 23 kinds of lithology combinations.The cyclic sedimentation record can be divided into 276 cycles, with the maximum thickness being 29.6m, the minimum thickness being 1.48m, and average thickness being 6.28m.Fisher diagrams and the spectrum analysis of logging curves reveal that the precession cycle is 19.2-23.4 ka, slope cycle is 39.1-51.4 ka, and eccentricity cycles is 95.3-403.1 ka.They are consistent with the period of ultra short term cycles, short-term cycle and medium-term cycles, respectively.So it is confirmed that the cyclic sedimentation record was controlled by the Milankovich cycle.In addition, it was also influenced by paleo-climate, sedimentary medium conjugate concussion and material supply.Finally, the cyclic-sedimentation dynamic model during low/high-stand period of Kongdian Formation in Jiyang Depression is established, and the original sedimentary dynamics and ancient environment of the cyclic sedimentation record under the control of Milankovich cycle are discussed.

Development characteristics and genetic mechanism of authigenic kaolinite in sandstone reservoirs of the Dongying Sag, Bohai Bay Basin

Zhang Yongwang, Zeng Jianhui, Qu Zhengyang, Chen Junbing

2015, 36(1):  73-79.  doi:10.11743/ogg20150109

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Arthroscopic characteristics, distribution and occurrence of kaolinite are analyzed through quantity thin section analysis, core observation, scanning electron microscope and X-ray powder diffraction.The results show that the kaolinite of sandstone reservoirs in Dongying Sag has two genetic types including authigenic kaolinite and terrigenous kaolinite.The authigenic kaolinites are common in the reservoirs.Microscopically, they show complete crystal form, and fill intergranular pores and dissolution pores of feldspar in typical sheet or vermicular shapes.The "spotted" filling feature of the authitgenic kaolinite aggregates are clear on cast thin sections.The terrigenous kaolinites are rare and often occur in shallow layers.They are formed in association with the non-clay minerals like clastic particles in deposition process.Based on the study mentioned above, the genetic mechanism of authigenic kaolinite is discussed.It is supposed that feldspar dissolution is the main material source for the formation of authigenic kaolinite.Sandstones with large grain size and well sorting have high content of kaolinite, indicating that, in addition to acid fluid environment and sufficient material supply, strong fluid dynamic is also an important controlling factor of authigenic kaolinite formation.

Fracture characteristics of sandstone in the 2^nd member of Upper Triassic Xujiahe Formation in Xinchang gas field, Western Sichuan Depression

Wang Zhengrong, Deng Hui, Huang Runqiu

2015, 36(1):  80-86.  doi:10.11743/ogg20150110

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Characteristics of fracture development in the 2nd member of the Upper Triassic Xujiahe Fm in Xinchang gas field were analyzed through outcrop observation, logging curve, image logging and analysis of borehole cores.The fractures in the studied interval are dominated by low angle fractures, followed by oblique fractures, high angle fractures and map cracking.And the strikes are mainly NEE, NE and SEE.The fractures can be divided into tectonic shear cracks, structural tensile fractures and bedding cleavages according to their genesis.On the basis of these studies, a three-dimensional numerical model of tectonic evolution was built according to the basic geological data and tectonic evolution features.Criteria for fracture identification were established based on theories of structural geology and taking the core observation and well logging analysis, laboratory test results into account.The calculation result shows that the T²⁽²⁾x, T²⁽⁴⁾x and T²⁽⁷⁾x sandstone roof fractures mainly developed near the fault zone.In the wing steep turn and structure peak area are main low angle shear fractures.And many tensile fractures are developed in the structure highs.Research results are basically consistent with exploration results, so the conclusion has a certain practical application and reference value.

Sedimentary system of the Late Permian Wujiaping Formation in the western Sichuan Basin

He Jiang, Zheng Rongcai, Hu Xin, Zhang Benjian, Yin Hong, Ma Hualing, Wang Yong, Feng Chunqiang

2015, 36(1):  87-95.  doi:10.11743/ogg20150111

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By means of detailed outcrop observation, lateral formation tracking and correlation, realistic writing of typical sedimentary section, systematic sampling and laboratory experimental analysis, detailed study was performed for the first time on sedimentary system of the Late Permian Wujiaping Formation in the western Sichuan Basin.The study found that the Dongwu movement at the end of the Early Permian was uplifting of fault block under tensional background.The Dongwu movement turned the southwest Kang-Dian ancient land into a provenance under the pushing and shoving by the ancient Tethys oceanic crust.Meanwhile, a trough graben area was formed in the northwest Guangyuan-Wangcang area due to the associated tensional subsidence.The relief in the area declines at low angle from southwest to northeast and indirectly controls the formation and lithofacies distribution of Wujiaping Formation.The sedimentary facies zones feature in wide and gradual variation.The Late Permian Wujiaping Formation was resulted from an high sea level transgression from northwest to southwest above the early weathering erosion interface.A denudation area and alluvial plain-coastal plain-coastal swamps-carbonate ramp sedimentary systems are successively developed from the southwest to northwest.Among these sedimentary systems, the moderate-shallow ramp bioclast beach was the most favorable reservoir facies belt with large thickness, wide distribution and near distance to the Guangyuan-Wangcang hydrocarbon kitchen, and it is capable of trapping hydrocarbons generated nearby.Several rounds of detailed digital seismic investigation have revealed many buried structures, providing new domains for enlarged exploration of carbonate gas reservoirs in the basin.

Sequence stratigraphic patterns and sand body prediction models of fault-depressed lacustrine basins:a case study from the Dongying Formation in the Nanpu Sag, Bohai Bay Basin

Dong Yuexia, Zhao Zhongxin, Wang Jianwei, Du Jingxia, Meng Lingjian, Diao Fan

2015, 36(1):  96-102.  doi:10.11743/ogg20150112

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Through analysis of sequence stratigraphic patterns in different structural belts, this paper illustrates the control of sequence stratigraphic pattern on sandbody distribution, and provides theoretical evidences for the sandbody prediction in fault-depressed lacustrine basin.Four sequence stratigraphic patterns in two different structural settings are identified based on the analysis of the sequence stratigraphic pattern and its control on reservoir sandbody in different structural settings of Dongying sedimentary period.They include the multiple faulted-slope-zone pattern, single faulted-slope zone pattern and transform zone pattern in the northern fault-break zone setting and the gentle slope-break pattern in the slope structure setting in southern beach area.On this basis, a sandbody prediction model was established to guide reservoir prediction which is of great significance for determining the distribution of favorable reservoir.

Main control factors and distribution prediction of high-quality carbonate reservoirs in the Nanpu Sag, Bohai Bay Basin

Cao Zhonghong, Zhang Hongchen, Liu Guoyong, Ren Miaosong, Fu Jiang, Wang Enze

2015, 36(1):  103-110.  doi:10.11743/ogg20150113

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Hydrocarbon accumulation conditions of carbonate buried-hill are favorable in Nanpu Sag, and hydrocarbon enrichment is controlled by multiple factors like stratigraphy, structure and reservoir.Development and distribution of quality reservoir are the focus of the research.In-depth analysis of drilling, logging, core and other data reveals that the main reservoir type is fractured-vuggy carbonate reservoirs in Nanpu Sag, with dissolution pores and vugs as the dominant reservoir space and fractures as the main channels connecting the pores and vugs.Carbonate sedimentary facies zones, diagenesis (including karstification), and tectonic process are the main factors controlling on the development of high-quality carbonate buried-hill reservoirs.The favorable sedimentary facies are the basis of reservoir development, the favorable diagenetic epigenesis is the guarantee of reservoir development and the favorable tectonic process is the key to reservoir development.The precision of reservoir prediction is significantly improved through comprehensive seismic and geological reservoir prediction based on layer subdivision.

Lithofacies and architectural characteristics of sandy braided river deposits:a case from outcrops of the Middle Jurassic Yungang Formation in the Datong Basin, Shanxi Province

Chen Bintao, Yu Xinghe, Wang Tianqi, Ma Fengliang, Li Shunli, Yang Lisha

2015, 36(1):  111-117.  doi:10.11743/ogg20150114

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Sandy braided river deposits have excellent physical properties, thus are important oil/gas reservoirs.In order to demonstrate the lithofacies and architectural characteristics of the sandy braided river reservoirs, and quantify the geometric properties and physical properties of architectural units, a systematic study for outcrops of sandy braided river deposits in the Middle Jurassic Yungang Formation in the Datong Basin has been conducted on the basis of outcrop observation, detailed interpretation of architectures, and laboratory analysis.Seven types of lithofacies in five associations have been identified.Five typical architectural units were identified in the sandy braided river deposits, including channel (CH), channel bar (CB), point bar (PB), abandoned channel (ACH), and overflowing sediments (OF).Among these architectural units, the channel and channel bar are the main architectural units with accumulative distribution frequency up to 78%.The thickness of channels ranges from 2.5 m to 6.5 m, width/thickness ratio is about 25-30, and the average porosity is 7.1%.The thickness of channel bars ranges from 2.5 m to 7.0 m, width/thickness ratio is about 30-35, and the average porosity is 7.8%.During the same depositional period, four basic combination types of the architectural units developed in the sandy braided river, namely CH-OF, CH/ACH-PB, CH-CB-CH, and CH/ACH-PB-OF.The spatial distribution of the architectural units in the different depositional periods is characterized by superposition or repetition of these four basic combination types in vertical and lateral.Channel and channel bar are the major reservoir types in the sandy braided river deposits, but the scale and physical properties of the later are better than the former.

Sedimentary characteristics of shallow-water delta distributary channel sand bodies: a case from Ⅱ-Ⅰ Formation of Fuyu oil layer in the Sanzhao Depression, Songliao Basin

Deng Qingjie, Hu Mingyi, Hu Zhonggui, Wu Yukun

2015, 36(1):  118-127.  doi:10.11743/ogg20150115

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Subtle lithologic reservoirs with shallow burial depth in the Ⅱ-Ⅰ Fms of Fuyu oil layers (FⅡ-FⅠ) are widely distributed in Sanzhao Depression, Songliao Basin, and are the major targets of tight oil exploration for reserve growth.The FⅡ-FⅠ in Sanzhao Depression are dominated by shallow water delta depositional systems featuring in complex change of sedimentary facies belt, and their main reservoir frameworks consist of distributary channel sandbodies.Based on detailed core observation of 53 wells and combining with logging data of more than 1 000 wells, 11 types of lithofacies were recognized in the distributary channel sandbodies of FⅡ-FⅠ in study area, and they were grouped into 3 lithofacies associations according to different datum level cycles.There are three types of interlayers in single distributary channel, including muddy interlayer, calcareous interlayer and conglomeratic siltstone, by which the internal architecture configuration of single distributary channel sand body was further analyzed.Comparison models for cotemporaneous channel sandbodies and interlayers were built through flattening of the tops of distributary channel sandbodies and were used to compare the sandbodies in respects of lithology, types of interlayer and shapes of logging curve.Methods were proposed for identifying the interwell cotemporaneous channel sandbodies between wells with small spacing within the sequence stratigraphic framework and the distribution of sandbodies was also discussed.Based on the comparative method above, combining with comparison of sandbodies by fence diagram and seismic attribute analysis, the distribution characteristics of single distributary channel sandbody were described, providing a geologic foundation for tight oil exploration and development.

Superimposition patterns of underwater distributary channel sands in deltaic front and its control on remaining oil distribution:a case study from K₁q⁴ in J19 block, Fuyu oilfield

Feng Congjun, Bao Zhidong, Dai Chunming, Zhang Zhaoqian

2015, 36(1):  128-135.  doi:10.11743/ogg20150116

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Taking the fourth member of the Quantou Formation in J19 block of Fuyu oilfield as an example, single sandbodies identification was performed within composite underwater distributary channels in delta front by integrating various data including cores, logging and production performance on the basis of sedimentary micro-facies.The results show that there are four main vertical superimposition patterns of single sandbodies, including separated type, overlap-type, overlay type and substitution type, and five lateral contact patterns, including interdistributary contact, embankment contact, butt-joint, side shear and substitution type.The corresponding identification marks are also summarized.The width of single sandbody is in the range from 200-800m and their thickness range from 4-8m.The tops of the separated type sandbodies are rich in remaining oil.In overlap-type, overlay type and substitutional type sandbodies are different in thickness and water injection direction, thus strongly influencing remaining oil distribution.Sandbodies of interdistributary contact, embankment contact and butt-joint kinds are not interconnected laterally, thus remaining oil possibly occurring in the flanks of the sandbodies.In contrast, sandbodies of side shear and substitutional type are well connected laterally, unfavorable for enrichment of remaining oil.

Sequence stratigraphy of the Upper Miocene-Pliocene deepwater deposits and its controlling factors in Rakhine Basin, Myanmar

Ma Hongxia, Sun hui, Shao Dali, Liu Yanhong, Ding Liangbo, Zou Chen, Yu Xinpei

2015, 36(1):  136-141.  doi:10.11743/ogg20150117

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High resolution 3D seismic data were used for the sequence stratigraphy division of the Upper Miocene-Pliocene deepwater gravity flow deposits in Rakhine Basin, Myanmar.Taking the continuous weak reflections of the TST-HST mudstones and the base of the thick channel incision and lobe sandstones as the third-order sequence boundaries, the upper Miocene-seabed deposits were divided into three third-order sequences, corresponding to the Upper Miocene, Pliocene and Pleistocene-seabed respectively.The Upper Miocene and Pliocene were selected as the focus of this study and were subdivided into three and two fourth-order sequences respectively according to the vertical evolution characteristics of the deepwater architectural elements.Each fourth-order sequence shows similar positive rhythm features of upward decreasing grain size, weakening denudation and lowering sand-to-gross ratio.The third-order sequence boundaries were caused by the regional large marine regressions, while the fourth-order sequence boundaries were resulted from the small-scale marine regressions.The development of sequence stratigraphies was mainly controlled by the sea level change, tectonic uplifting and climate.The sea level change influenced the deposition variation.And the tectonic uplifting and the climate controlled the sediment supply volume which affected the stacking styles of the fourth-order sequence.Especially during 7-8 Ma, the rapid uplifting of the Tibetan strengthened the south Asian monsoon, intensified erosion, and thus increased sediment supply.Consequently, the lobe sandstones increased and the channel incision strengthened during 7-8 Ma.

Rational injection-production pressure system in water-drive oilfields

Tian Xuanhua, Lu Zhengyuan, Hu Gang, Liu Weixia

2015, 36(1):  142-147,153.  doi:10.11743/ogg20150118

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Optimization of rational injection-production pressure system is a key part of developing water flooding oilfield.However, the methods widely used previously have certain disadvantages.The water-absorption and fluid productivity index method does not take into consideration factors such as the imbalance between injection and production fluids, density difference between oil and water, and their volume factors.The method of ‘water absorption and fluid productivity index and injection-production ratio’ignores density difference between oil and water and volume factor.The method of ‘index ratio of water-absorption to fluid-productivity and pressure difference between injection and production well’has no theoretical and practical significances.The method of‘considering single well and reservoir pressure variations pays no attention to the influences of start-up pressure of water injection well and start-up pressure of production well on oilfield development effects.To solve the above-mentioned problems, a new approach to optimize the injection-production pressure system in water flooding oilfield was proposed based on the pressure profile of injection-production.Compared with the previous ones, the new method is comprehensive, taking into account such factors as injection-production imbalance, density difference between oil and water, volume factor, start-up pressure gradient of injection wells and start-up pressure gradient of production wells.Experiments show that it can be applied to parameter calculation of all reservoir types and all reservoir pressure distributions in a water flooding oilfield.For example, it has been used to calculate the rational pressure system of injection-production of the No.1-3 sandstone reservoirs in the 2^nd Member of Shahejie Formation of Shengyi block, Shengtuo oilfield.And the result shows that the ratiional ratio of oil to water wells is 1.42, the rational formation pressure-keeping level is 17.29 MPa while the rational fluid-production volume and water-injection are 14 572.41 m³/d and 15 906.88 m³/d respectively, with 12 452.41 m³/d and 13566.88 m³/d more than before, and with a remarkable increase of fluid production and water injection.

Calculation of the minimum commercial reserves of petroleum reservoirs

Zhang Zhonghua, Zhou Jitao

2015, 36(1):  148-153.  doi:10.11743/ogg20150119

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Based on reservoir exploration and development practices, this paper defines the minimum commercial reserves of petroleum reservoirs and explains the specific connotations of the minimum commercial recoverable reserves, the minimum business proved reserves and the minimum business resources of reservoirs.By studying the development regularities and production change patterns of reservoirs in different regions and in combination with the principles of input-output analysis, a universal method was presented for calculating the minimum commercial reserves based on the reservoir development conceptual design.The relationship among reservoir development concept design parameters and cash inflow and outflow parameter models was established first and then used to build a linear correlation model of reservoir reserves to net present value.For a given reservoir, this model theoretically revealed the characteristics of variation of the minimum commercial reserves under different economic conditions.The method can rapidly evaluate the minimum commercial reserves under different boundary conditions by directly using the economic parameters of reservoir exploration and development, the parameters of reserves grade and the parameters of the development concept plan.Therefore, it can provide efficient technical supports to the economic benefits ranking of exploration projects in different oil fields, the ranking of potential targets of producing proven reserves, and the demonstration of reservoir evaluation projects during oilfield development and production capacity building goals in new blocks.

Concept, method and application of geological risk dependency indicating petroleum discovery

Sheng Xiujie, Jin Zhijun, Xiao Ye, Wang Yigang, Jiang Han

2015, 36(1):  154-161.  doi:10.11743/ogg20150120

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The combination probability, the possibility that at least one segment contains hydrocarbons, can be used to assess the discovery probability of a trap.Obviously,‘at least one segment containing oil/gas’ reflects all possibilities of trap combinations.However, some traps should not be treated as one combination due to the constraint of special geological conditions.The trap combinations have direct influences on the estimation of geological resource.In order to calculate trap combination probability under the constraint of geologic models, this paper first cleared geological meaning of current evaluation model for segment and demystified its mysterious hype.It is in fact a classical Bayes mathematical model consisting of marginal and conditional probability, which quantifies separately the overall accumulation conditions or play-level and local accumulation conditions.Geological correlations do exist among different traps when hydrocarbons accumulate in them, thus the evaluation of single trap should be based on the prerequisite of possibility of overall hydrocarbon accumulation.Secondly, corresponding to the value range of marginal probability, this paper recognizes three geological risk dependence types including full independence, partial dependence and full dependence.These dependence types can directly determine which traps are concordant with current geologic knowledge.Finally, an improved probability tree technique was designed for the petroleum integrated assessment software (PetroV).When integrated with the non-deterministic volumetric method, it can realize resource volume estimation through‘summation of probability combinations based on geological risk dependency’.Case study shows that geological risk dependence types play a key role in quantitative evaluation of traps and mapping of uncertain petroleum resource distribution corresponding to reasonable geologic model interpretations.

SLD-PR simulation method for shale adsorption isotherm and its application

Hu Zhiming, Guo Wei, Xiong Wei, Zuo Luo, Shen Rui, Gao Shusheng, Yang Farong, Miao Xue

2015, 36(1):  162-167.  doi:10.11743/ogg20150121

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Shale gas is mainly composed of adsorption gas and free gas.Adsorption gas content directly affects the geolo-gical reserves and well production for a shale gas reservoir.In order to accurately measure adsorption gas content, isothermal adsorption experiments were performed within temperature range of 25-45 ℃ and pressure range of 0-8 MPa on the Longmaxi Fm shale in South Sichuan Basin.Results indicate that shale adsorption capacity decreases as temperature increases.In addition, shale adsorption isotherms at different temperatures were calculated by using the simplified local density (SLD-PR) method and compared with the experimental results.The comparison shows that this method can be used to calculate shale adsorption isotherm.The SLD-PR method can be used to predict shale adsorption isotherm under reservoir pressure and temperature conditions, thus overcoming the disadvantage that the errors of isotherm experimental measurements under high temperature and pressure are large.Comparison between the calculated adsorption gas content by the SLD-PR method and that by the Langmuir method indicates that the former is more accurate and reliable than the latter.

Application of joint PP and PS inversion to the exploration of shale-gas reservoirs

Yuan Shukun, Chen Kaiyuan, Bob A Hardage, Feng Zhiqiang, Wei Shuijian

2015, 36(1):  168-174.  doi:10.11743/ogg20150122

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In recent years, the development of shale oil and gas shows that shale heterogeneity and lateral orientation have relatively great impacts on single well shale gas production, recovery factor and the economy of shale gas exploitation, and natural micro-fracture is the main factor resulting in shale heterogeneity.Accordingly, to carry out research on the natural micro-fractures and prediction of sweet spots within shale has become an inevitable choice for successful emplacement of high-yielding wells and improving economic benefits of shale gas exploitation.Based on the high resolution 3C/3D seismic data in Marcellus shale play within Appalachian Basin, North America, natural micro-fracture zone of Marcellus shale was predicted by means of fast and slow converted shear wave(PSV-1/PSV-2)integrated interpretation, then the open/closed fractures and gas-bearing property of extensional micro-fractures were separately identified and detected by utilizing combined attribute parameters like joint inversion density, velocity ratio of compressional and converted wave(v_P/v_S)extracted from joint inversion of compressional wave and converted shear wave(PP-PS).In addition, drilling data were used to verify the sweet spots predicted by geophysical method in Marcellus shale.Joint inversion technique(PP-PS) has outstanding advantages in natural extensional micro-fractures identification and gas-bearing detection, which can effectively reduce the drilling risk.