Petroleum Exploration and Development

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Shale gas in China: Characteristics, challenges and prospects (Ⅰ)

Zou Caineng; Dong Dazhong; Wang Yuman; Li Xinjing; Huang Jinliang; Wang Shufang; Guan Quanzhong; Zhang Chenchen; Wang Hongyan; Liu Honglin; Bai Wenhua; Liang Feng; Lin Wen; Zhao Qun; Liu Dexun; Yang Zhi; Liang Pingping; Sun Shasha and Qiu Zhen

. 2015, 42(6): 689-701.

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The main factors controlling the enrichment and high yield of shale gas were analyzed based on the recent research progress of depositional model and reservoir characterization of organic-rich shale in China. The study determines the space-time comparison basis of graptolite sequence in the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation and proposes the important depositional pattern of marine organic-rich shale: stable ocean basin with low subsidence rate, high sea level, semi-enclosed water body, and low sedimentation rate. Deposited in the stage of Late Ordovician-Early Silurian, the superior shale with thickness of 20?80 m and total organic carbon (TOC) content of 2.0%?8.4% was developed in large deep-water shelf environment which is favorable for black shale development. Based on the comparison among the Jiaoshiba, Changning and Weiyuan shale gas fields, it is believed that reservoirs of scale are mainly controlled by shale rich in biogenic silica and calcium, moderate thermal maturity, high matrix porosity, and abundant fracture. The shales in the Wufeng and Longmaxi formations are characterized by porosity of 3.0%?8.4%, permeability of 0.000 2×10?3?0.500 0×10?3 μm2, stable areal distribution of matrix pore volume and their constituents, great variation in fracture and pore characteristics among different tectonic regions as well as different well fields and different intervals in the same tectonic. The Cambrian Qiongzhusi shale features poor physical properties with the porosity of 1.5%?2.9% and the permeability of 0.001×10?3?0.010×10?3 μm2, resulted from the carbonization of organic matter, high crystallinity of clay minerals and later filling in bioclastic intragranular pores. Four factors controlling the accumulation and high production of shale gas were confirmed: depositional environment, thermal evolution, pore and fracture development, and tectonic preservation condition; two special features were found: high thermal maturity (Ro of 2.0%?3.5%) and overpressure of reservoir (pressure coefficient of 1.3?2.1); and two enrichment modes were summarized: “structural sweet spots” and “continuous sweet area”.

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Features and origin of natural gas in the Sinian–Cambrian of central Sichuan paleo-uplift, Sichuan Basin, SW China

Wei Guoqi; Xie Zengye; Song Jiarong; Yang Wei; Wang Zhihong; Li Jian; Wang Dongliang; Li Zhisheng and Xie Wuren

. 2015, 42(6): 702-711.

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Based on the new drilling data and field outcrop data of the Gaoshiti–Moxi area, the geochemical characteristics of the Sinian-Cambrian natural gas are studied and analyzed, including gas composition, isotope, light hydrocarbon, kerogen carbon isotope and reservoir bitumen biomarkers etc. The results show that: (1) The natural gases of the Sinian Dengying Formation and Cambrian Longwangmiao Formation, mainly composed of hydrocarbon gas, are typical dry gas. However, the natural gas of the Dengying Formation is characterized by higer dry coefficient, lower content of hydrocarbon gas and higher content of non-hydrocarbon gas. The main difference in non-hydrocarbon gases are the contents of N2, CO2, H2S and He, the small composition differences between the natural gas of Dengying Formation and that of Longwangmiao Formation are mainly caused by maturity differences of source rocks and H2S generated by reaction between sulfide mineral and hydrocarbons. (2) There are obvious differences in δ13C2 between the natural gases in Dengying Formation and Longwangmiao Formation, showing different parent materials of them. (3) There are large differences in δ2H between the natural gases of Dengying Formation and Longwangmiao Formation, showing the different water salinities of their source rock depositional environment. (4) The average kerogen carbon isotope values of the Lower Cambrian shale, Dengying Formation mudstone, Doushantuo Formation mudstone and Dengying Formation carbonates are ?32.8‰, ?31.9‰, ?30.7‰ and ?27.8‰ respectively. (5) The ratio of 4-methyl dibenzothiophene to 1-methyl dibenzothiophene of Dengying Formation bitumen is between that of Qiongzhusi Formation and Dengying Formation source rocks. It is believed that the Sinian-Cambrian natural gas in the Gaoshiti-Moxi area is mainly oil cracking gas, the Sinian natural gases come from the Sinian and Cambrian source rocks, and the Cambrian natural gases mainly come from Cambrian source rock.

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Strike-slip superimposed Qaidam basin and its control on oil and gas accumulation

Fu Suotang; Ma Dade; Guo Zhaojie and Cheng Feng

. 2015, 42(6): 712-722.

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Based on detailed field survey in the western Qaidam Basin, combined with petroleum exploration practices in recent years, this study suggests that the Qaidam Basin is a strike-slip superimposed basin jointly controlled by the left-lateral strike-slip Altyn Tagh and East Kunlun faults. The Altyn Tagh fault acts as the major controlling boundary, while the East Kunlun fault only controls the local evolution of the southern edge of the basin. To the east, the northern Qaidam-Qilian Shan thrust-fold belt passively accommodates the northeastward displacement along the Altyn Tagh fault through NE-SW directed shortening. In the India-Asia collision background, the left-lateral strike-slip faulting along the Altyn Tagh fault initiated from the early Eocene, forcing the Qaidam Basin to move northeastward, causing the thrust and slip deformation of the NW-SE faults in northern Qaidam margin-Qilian Mountain area, and the deposition of the Cenozoic since the Paleogene Lulehe Formation. During the Paleogene, the northern Qaidam Basin developed coarse-grained sediments like that in a foreland basin, forming poor quality source rocks; while the southwestern Qaidam Basin was an extensional sag basin where good quality source rocks deposited. By the early Miocene, left-lateral faulting along the Kunlun fault became active, leading to the formation of a series of en-echelon faults (e.g. the Kunbei fault, the Arlar fault and the Hongliuquan fault). These faults gradually migrated northward, their kinematics changing from left-lateral strike-slip motion to NE-SW transpression. Strike-slip-related structures controlled by those faults (e.g. the Yingxiongling structure) are ideal places for oil and gas accumulation from Paleogene source rocks. To sum up, the Qaidam Basin is a strike-slip superimposed basin jointly controlled by the left-lateral strike-slip Altyn Tagh and East Kunlun faults. The temporal and spatial superimposition of these two strike-slip faults during the Cenozoic controlled the evolution of the basin as well as the oil and gas accumulation.

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Re-exploration program for petroleum-rich sags and its significance in Bohai Bay Basin, East China

Zhao Xianzheng; Wang Quan; Jin Fengming; Luo Ning; Fan Bingda; Li Xin; Qin Fengqi and LI Xu

. 2015, 42(6): 723-733.

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A comprehensive analysis is done to investigate the exploration maturity and exploration potential in the petroleum-rich sags in the Bohai Bay Basin, indicating that the re-exploration program is of great significance. The advances in geological theories, key engineering technologies and exploration methods involved in the re-exploration program are described. Taking the Raoyang sag as an example, the study documents how the program was conducted and discusses its promising future of application. Petroleum-rich sags, which with an oil resource abundance of greater than 20×104 t/km2 and a total oil resource of over 3×108 t, are the main domains for petroleum exploration and production in the Bohai Bay Basin. With a proven rate of more than 50%, these petroleum-rich sags have entered the high maturity exploration stage and discovery of new oil and gas reserves has become more and more difficult. However, the undiscovered oil resources in these sags are abundant and amount to 105×108 t, so that they are still the main exploration domains in the Bohai Bay Basin. With the petroleum-rich sags in the Jizhong depression of the Bohai Bay Basin as an example of the re-exploration program, the study presents a detailed documentation of oil accumulation in subsags, reservoir-forming in the subtle buried hills, and oil migration and accumulation in the weakly deformed structural slopes. It deals with the advances in the merged 3-D seismic prospecting over an entire sag, facies-based reservoir prediction, stimulation techniques for complex reservoirs and fast efficient drilling techniques. Furthermore, it proposes the re-exploration program, which comprises a new round of overall exploration philosophy, new evaluation and planning. It discusses the important roles played by the re-exploration program in sustaining the reserve additions in the highly explored petroleum-rich sags.

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Re-determining source faults of the Upper Cretaceous Putaohua oil layer in Sanzhao sag of Songliao Basin, NE China

Wang Yougong; Yan Meng; Lang Yue; Fu Guang and Li Xin

. 2015, 42(6): 734-740.

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From the deformation characteristics of two walls of a fault caused by fault activities, the activation of faults in the critical moment of oil and gas accumulation (structural inversion period) was analyzed to determine the source faults in the Upper Cretaceous Putaohua oil layer of the Sanzhao sag in Songliao Basin. Based on the previous classification and research results of activity patterns of the faults in the Sanzhao sag, the analysis of the structural deformation characteristics during the deposition of the 2nd and 3rd members of the Upper Cretaceous Nenjiang Formation and the inversion reveals that the feature of cutting to T06 reflection layer (bottom interface of the third member of the Nenjiang Formation) can not be taken as the basis to judge whether the faults were activated during the inversion or not. But during the structural inversion period, the structural deformation caused by faults would lead to fault-propagation inverted folds and fault-bend inverted folds, which would further lead to obvious deformation differences between hanging walls and foot walls of faults, this can be taken as the basis to determine if the faults were activated or not in the inversion period, and then the source faults of the Putaohua oil layer can be determined. Furthermore the source faults can be divided into two kinds, hidden faults and penetrating faults, according to if the source faults cut through layers of inversion period or not. These two kinds of source faults show more obvious control over the planar oil distribution in the Putaohua layer than the previous study results.

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Characteristics and origin of tuff-type tight oil in Jimusar Depression, Junggar Basin, NW China

Jiang Yiqin; Liu Yiqun; Yang Zhao; Nan Yun; Wang Rui; Zhou Peng; Yang Yanjun; Kou Junyi and Zhou Ningchao

. 2015, 42(6): 741-749.

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Based on core and thin section observation, and combined with X-ray diffraction, electron probe and geochemical analysis, the characteristics and origin of tuff tight oil of the Permian Lucaogou Formation in the Jimusar depression, Junggar Basin were examined. There are tuff, tuffite and tuffaceous dolomite interlaid in the sedimentary rocks of the Lucaogou Formation. The alkali feldspar and quartz in the tuff are rich in strontium, which, according to mineral geochemical analysis, are originated from alkaline-peralkaline magmatic rocks. The Sr isotope ratio (87Sr/86Sr) of dolomite is similar to that of mantle, which shows minerals of tuff were formed in volcanism-related hydrothermal environments. High Sr/Ba and δ13C of dolomite, and occurrence of halite under microscope suggest that the Lucaogou Formation was deposited in high salinity environment. High content of magnesium and iron ions related to volcanism and hydrotherm, and high salinity environment contributed to the precipitation of dolomite. The distribution of tight oil, organic matter abundance of source rock and reservoir physical properties show that it is the rich nutrients provided by volcanic activity that controlled the formation of high abundance source rock; tuff, tuffaceous dolomite with plenty of residual inter-granular pores and dissolved pores are favorable reservoir sections; and tuff controls the formation and distribution of tight oil.

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Division and resources evaluation of hydrocarbon plays in the Amu Darya Basin, Central Asia

Yu Yixin; Yin Jinyin; Zheng Junzhang; Li Feng; Tao Chongzhi; Xu Xiaolong and Wu Hang

. 2015, 42(6): 750-756.

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Based on the newest geological data and exploration achievements and the analysis of hydrocarbon accumulation elements and distribution rules of oil and gas, the hydrocarbon plays are divided according to the reservoirs in the Amu Darya basin, central Asia. The hydrocarbon plays are evaluated in terms of resources potential and geologic risk, and the favorable hydrocarbon plays are selected using the double factors method of resources-geological risks. Ten hydrocarbon plays have been divided into in the major reservoirs, including the Cenomanian to Turonian sandstones of the Upper Cretaceous, the Hauterivian to Albian sandstones of the Lower Cretaceous, the Callovian to Oxfordian carbonates of the Upper Jurassic, and the Middle-Lower Jurassic sandstones. The undiscovered petroleum resources of the plays, evaluated by the Monte Carlo method, are about 3 308 million tons, in which gas accounts for more than 98%. Considering the geological risks evaluation of the key hydrocarbon elements of reservoir, trap, migration and preservation, the favorable plays are evaluated and selected using the double factors method of resources-geological risks: two plays of class I, one play of class IIa, two plays of class IIb, three plays of class III, one play of class IVa, and one play of class IVc. The most favorable exploration objectives are the carbonate reservoirs of the Upper Jurassic Callovian-Oxfordian in the Murgab depression.

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Quantitative research on tight oil microscopic state of Chang 7 Member of Triassic Yanchang Formation in Ordos Basin, NW China

Wang Minglei; Zhang Sui’an; Zhang Fudong; Liu Yuting; Guan Hui; Li Jun; Shao Liyan; Yang Shen and She Yuanqi

. 2015, 42(6): 757-762.

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With nuclear magnetic resonance (NMR) and micrometer-nanometer CT Scanning technology, quantitative research was carried out of the micro-existing state of tight oil in the Chang7 Member of the Triassic Yanchang Formation in the Ordos Basin. The total reserves of the tight oil in the reservoirs were determined using NMR technology. The initial oil saturation was measured as 63.99%. The 2-D slice images of the tight oil reservoirs were obtained using CT Scanning technology, and the 3-D images were acquired after digital synthesis processing. Accordingly, the existence states of the tight oil in the reservoirs are divided into six types, namely thin film form, cluster form, throat form, emulsion form, particle form and isolation form. It is found by quantitative calculation of the contents of tight oil in different existence states of tight oil that the emulsion form and thin film form are the main existence states, which account for 70% of the total amount of the tight oil in the reservoirs, followed by the cluster and particle forms. The contents of isolation form and throat form tight oil are low. The contents of tight oil in various existence states are related to initial water saturation, clay mineral content and pores structure of the reservoirs.

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Geological characteristics and exploration potential of diamictite tight oil in the second Member of the Permian Lucaogou Formation, Santanghu Basin, NW China

Li Xinning; Ma Qiang; Liang Hui; Zhang Pin; Zhang Qi; Jia Xueli; Pu Zhenshan; Yan Ligang and Meng Yuanlin

. 2015, 42(6): 763-771.

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Based on the latest exploration data of tight oil, the evaluation of the “seven properties” relation of diamictite tight oil in the second Member of the Permian Lucaogou Formation in Santanghu Basin was carried out. The second Member of the Lucaogou Formation developed a new suit of high-quality hydrocarbon source rocks, which are characterized by wedging distribution, big thickness, high organic content and good organic type, and the overall being in the oil-generating window. Complex in lithology, the second Member of the Lucaogou Formation is a set of laminated structure diamictite combination composed of detrital material of terrigenous origin, dust fall, carbonate rock in variable proportions. With low natural gamma and high electrical resistivity, strong heterogeneity, micropores as main matrix porosity, it has features of ultra-low porosity and extra-low permeability; the fractures in it provide some reservoir space, and make great contribution to permeability. The Member has good oiliness (oil saturation from conventional core analysis is 15%-80%), high content of brittle minerals (80%?90%), clay mineral content of less than 10% in general; core sensitivity test shows that it varies widely in water sensitivity and velocity sensitivity, and is weak in acid sensitivity. Through evaluating the “seven properties” relation, it is concluded that the main control factors of the tight oil layer are the maturity of hydrocarbon source rock and reservoir physical property. The “sweet spots” of diamictite tight oil in the second Member of the Lucaogou Formation were selected, that is, the areas with favorable reservoir physical properties in the mature hydrocarbon source rock of the sag.

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Molecular dynamics simulation of liquid alkane occurrence state in pores and fractures of shale organic matter

Wang Sen; Feng Qihong; Zha Ming; Lu Shuangfang; Qin Yong; Xia Tian and Zhang Chi

. 2015, 42(6): 772-778.

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Molecular dynamics simulation was used to study the occurrence state of liquid alkane in pores and fractures of shale organic matter. On the basis of OPLS (Optimized Potentials for Liquid Simulation) force field, the alkane densities under different pressures and temperatures were calculated; the comparison with experimental results validated the efficiency of this approach. With n-heptane as an example, the basic occurrence behaviors of alkanes in the pores and fractures of organic matter were analyzed under formation conditions, and the effects of fracture width, thermal maturity of organic matter, carbon chain length and isomers were also discussed. Results show that: (1) The density distribution of the alkanes across the pores and fractures is not uniform, but presents a periodic fluctuation; (2) A “solid-like” alkane layer will form in the vicinity of the solid surface, and its density approximates to 1.9?2.7 times greater than that of the bulk-fluid; (3) Multiple adsorption layers are always shown for liquid alkanes and the thickness of each layer is 0.48 nm; the total number of adsorbed layers is influenced by the fracture width and fluid composition. Finally, using this approach, the proportion of adsorbed-phase (18.2%) is determined for oil in an organic matter slit.

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Buried hill karst reservoirs and their controls on productivity

Wang Jincai; Zhao Lun; Zhang Xiangzhong; Yang Zhigang; Cao Haili; Chen Li; Shan Fachao and Liu Minghui

. 2015, 42(6): 779-786.

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The concept model of ancient buried hill karst reservoirs was built taking the NWKK carbonate rock oilfield in the South Turgay Basin in Kazakhstan as an example, and the characteristics of karst reservoirs and their controls on productivity were analyzed in vertical and horizontal directions. Vertically, the karst reservoirs can be subdivided into, from top to bottom, weathering crust zone, epikarst zone, caves zone, vadose zone and phreatic zone, in which the development of fractures is strengthened gradually; Six reservoir types, breccia pore, cave, vug, fracture-vug, fracture-pore and pore, were developed; Each karst zone has high oil production and low water cut in the initial stage because of the developed fractures and karst caves, but the production declines rapidly and the water cut rises fast. Horizontally, the karst reservoir characteristics are controlled by structure altitude and ancient lithofacies: the ancient buried hill with high structure altitude and loose lithology suffers from stronger weathering and leaching, has much more solution caves and holes, the main reservoir types are breccia pore, cave, and vug, while the ancient buried hill with low structure altitude and compacted lithology has highly developed fractures and stronger communication with bottom water, the main reservoir types are fracture-vug and fracture-pore, and the reservoirs have better productivity effect but rapid production declines and water cut rising. Different areas in plane should adopt different development techniques and policies.

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Application of Lorenz-curve model to stratified water injection evaluation

Gao Dapeng; Ye Jigen; Hu Yunpeng; Dong Yifu; Zhu Zhenkun; Yuan He; Huang Lei and Wang Shuyi

. 2015, 42(6): 787-793.

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To evaluate the effect of stratified water injection accurately during different development stages, a Lorenz-curve model was constructed upon a modified four-parameter Sarabia-Lorenz-curve model with water injectivity test data over years, and the relationship between accumulative perforated sandstone thickness and injected water volume of single wells was described by the model. Three evaluation indexes, dimensionless water injectivity intensity, vertical sweep efficiency and water-injection non-balanced degree, and their calculation were presented. Dimensionless water injectivity intensity is used to evaluate the distribution and balanced degree of water injectivity intensity, vertical sweep efficiency is the proportion of oil layers that produce oil, and water-injection non-balanced degree illustrates the overall water-injection balanced condition, then the model is solved by particle swarm optimization algorithm. Thirty-eight stratified water injection wells were evaluated in the Daqing Xingshugang oilfield. And the factors influencing the effect of water injection in single wells were studied considering segments construction, water allocation projects and reservoir physical properties. Finally, technological limits of stratified water injection were proposed under extreme high water-cut and recovery.

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Hydraulic fracture initiation mechanism in the definite plane perforating technology of horizontal well

Liu He; Wang Suling; Xu Jianguo and Zhao Chenxu

. 2015, 42(6): 794-800.

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The local stress calculation model of the definite plane perforation for the horizontal wells was built, and the mechanism of fracture initiation and the influence rules of the wellbore location and perforating parameters on the fracture initiation pressure were analyzed. The in-situ stress model of three-dimensional fluid-solid coupling was established according to the theory of percolation mechanics, and the method for determining the initiation pressure of the definite plane perforation was presented according to the maximum tensile stress theory and was verified by application example. The calculation and analysis reveal: for the in-situ stress fields of normal faults and reverse faults, the initiation of hydraulic fractures happens on the perforated plane during the definite plane perforation, a wide, short, vertical fracture forms in the in-situ stress field of a normal fault, and a narrow, long, diverted fracture forms in the in-situ stress field of a reverse fault; for the in-situ stress field of a normal fault, the greater the wellbore azimuth and inclination angle are, the lower the initiation pressure is; for the in-situ stress field of a reverse fault, the larger the wellbore azimuth angle or the smaller the wellbore inclination angle is, the lower the initiation pressure is; the smaller the perforation angle, the greater the perforating depth, or the larger the perforation diameter is, the lower the initiation pressure of definite plane perforation is.

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Environmental impacts of hydraulic fracturing in shale gas development in the United States

Zhang Dongxiao and Yang Tingyun

. 2015, 42(6): 801-807.

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Through comprehensive investigation of the environmental issues in shale gas development in the US, the environmental impacts of hydraulic fracturing in shale gas development are summarized to provide reference for the shale gas development and management in China. The environmental risks of large-scale commercial shale gas development in the United States include water consumption, water contamination, seismic inducement and air pollution. Compared to conventional oil and gas production and other energy producing industries, shale gas development is not exactly “high-water-consuming” in terms of water consuming intensity. Its water consumption, accounting for a small proportion of the total regional water consumption, will not add much more stress on water supply. In terms of water pollution, hydraulic fracturing is unlikely to cause fractures to directly connect reservoir to the shallow aquifer, the known contamination cases are most likely related to faulty well completion, therefore well integrity is the key to the prevention of contamination; the flow-back fluids in large scale shale gas development have the characteristics of large quantity, many kinds of pollutants and complex composition, thus improper treatment would lead to serious contamination, and continuous monitoring and assessment of the pollutants are necessary. Existing evidence shows that hydraulic fracturing is unlikely to trigger destructive earthquakes. Greenhouse gas emissions in the life cycle of shale gas wells were estimated differently, but no doubt more effective measures should be taken to minimize leakage. The research priorities include contamination monitoring program design, detection indicators, moving pattern of hydraulic fracturing fluid and formation fluid, the effects of shale gas development on high salinity formation water and methane migration, and treatment and re-use of flow-back fluid.

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Multi axial high cycle fatigue life model optimization for drilling tools

Narayanan Govindarajan

. 2015, 42(6): 808-811.

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The fatigue life model was optimized in terms of the multi axial high cycle fatigue failures of drilling tools. Based on the multi axial fatigue theory, the stress state under the non-proportional loading and the cracking behaviour of the material under multi axial fatigue were analyzed, the multi axial fatigue models were summarized, and the Dang Van model was recommended for judging whether or not the drilling tool will be subjected to fatigue failure under the certain stress state. The fundamental criterion, derivation principle, application scope and fatigue limit calculation method were introduced. The Dang Van model was validated with field failures of the drive shaft of stabilizer steering stator which was used in the drilling process of oil and gas fields, and compared with the conventional mean stress model. The results show that the mean stress model predicts in a over conservative way, and the Dang Van model is more applicable for predicting multi axial high cycle fatigue life of drilling tools.

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Finite element modelling of rock mass cutting by cutters for PDC drill bits

Pryhorovska T O; Chaplinskiy S S and Kudriavtsev I O

. 2015, 42(6): 812-816.

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A finite element model of the process of polycrystalline diamond compact (PDC) drill bit cutters cutting rocks was built, and the rock linear and circular cutting processes for different shapes of PDC drill bit cutters were simulated. The following initial data was stated before modelling: spatial form of cutter, cutting speed, cutting depth, rheological model of the processed material, and frictional model. Simulation results show that: there is no essential difference between curricular cutting and linear cutting; all the obtained relations of cutting forces were oscillatory and unevenly for all types of cutters; cutting depth increasing causes oscillation amplitude increasing, although no clear relationship between the fluctuations amplitude and the cutting depth is observed for the same cutter; for cutting depth in 0.5 mm and 1.0 mm, the average cutting force decreases when the cutting parameters are stable, while for cutting depth in 2.0 mm, the stable cutting regime is not accompanied by average cutting force decreasing; the cutting forces are smaller for spherical shape cutter and pick-shaped cutter, and bigger for tapered shape cutter and cutters with bevel and flat; the number of peaks per unit time on fluctuation diagram: the minimum value for flat cutter, maximum value for spherical shape cutter.

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Three-dimentional hydrocarbon migration and accumulation modeling technique based on finite volume method

Guo Qiulin; Chen Ningsheng; Xie Hongbing; Wu Xiaozhi; Liu Jifeng; Zhao Xiran; Gao Rili and Hu Junwen

. 2015, 42(6): 817-825.

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Aiming at the issue that the application effect of current 3-D hydrocarbon migration and accumulation modeling technique cannot meet the actual requirement because of over-simplified geologic model, a 3-D dynamic geologic model using PEBI grid in bedding and columnar shape was established, which can be used to solve the heterogeneity in reservoirs of various sedimentary facies, and to reduce the effect of mixed lithologies on modeling accuracy. A 3-D numerical modeling technique based on finite volume method was established, including the construction of variable grid flow equation, decomposition and calculation of full-tensor permeability, and calculation of conductivity etc. Some related processing techniques, such as smoothing of key parameter curves, stability processing of upstream and downstream of grid flow, etc. were used to improve the convergence of Newton’s iteration. Automatic adjustment of time step and multi-core parallel computation were taken to enhance the running efficiency of the software. In a case study of Nanpu sag in the Bohai Bay Basin, the hydrocarbon migration and accumulation process, oil saturation and hydrocarbon resources abundance in various periods were simulated, the modeled oil saturation, accumulation quantity and hydrocarbon distribution locations coincide with current exploration results. The results also showed that the proved ratio of hydrocarbon resources in target layers is 84.4%, the majority of the resources are distributed in Block B and Block C, and it is predicted that undiscovered resources are mainly near Well NP2-16 in Block C and in the structure north of Well NP5-4 in Block A.

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Development techniques of multi-layer tight gas reservoirs in mining rights overlapping blocks: A case study of the Shenmu gas field, Ordos Basin, NW China

Wu Lichao; Zhu Yushuang; Liu Yanxia; Zhou Zhaohua and He Dongbo

. 2015, 42(6): 826-832.

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The difficulties of making joint development of coal and natural gas were examined and the technical countermeasures were given through studying the case of the Shenmu gas field of the Ordos Basin, where the mining rights of coal and natural gas overlap completely. Based on the study of the main controlling factors of the distribution of favorable areas in the Upper and Lower Paleozoic formations, technical measures for different areas were determined considering well type, well pattern, efficient drilling and production, and ground gathering technology. The results show: The mining rights overlapping area of coal and natural gas can be developed jointly. The effective reservoirs of the multi-layer tight gas reservoirs can be divided horizontally into the superposition area for multi-boundaries sand body, multi-layers sand body and isolation sand body in the Upper Paleozoic formations, and the superposition area for effective reservoirs in the Upper and Lower Paleozoic formations. A cluster well group which includes nine wells is the optimal well pattern. Different reservoir area should be developed by different well type and patterns. The construction and development period of gas reservoirs will be shortened by the application of cluster well group, optimized technologies of drilling and production, and ground supporting facilities. Practice shows that the three dimensional development of the multi-layer tight gas reservoirs is also realized in the Upper and Lower Paleozoic when the joint development of coal and natural gas is done in the mining rights overlapping areas.

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23 December 2015, Volume 42 Issue 6