Petroleum Exploration and Development

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Formation and distribution of large low-permeability lithologic oil regions in Huaqing, Ordos Basin

Yang Hua; Fu Jinhua; He Haiqing; Liu Xianyang; Zhang Zhongyi and Deng Xiuqin

, 2012, 39(6): 2085-0.

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Through in-depth analysis of sedimentary source, lake basin shape and tectonic events as well as careful study of high quality source rocks, reservoir-forming force and history in the Huaqing area, Ordos Basin, the accumulation mode of large low-permeability lithologic oil regions in the middle of the lake basin was established. The Ordos Basin is a typical inland depressed basin during the depositional period of the Upper Triassic Yanchang Formation. Rich-nutrient lake-basin sediments are developed in the Chang-7 Member during the maximum flooding period. High-quality source rocks of the Chang-7 Member have the characteristics of high abundance of organic matter, strong ability of hydrocarbon generation and expulsion, and wide distribution in Huaqing in the central basin. Delta is developed extensively in the depositional period of Chang-6 Member. Influenced by rich provenance and the bottom shape of slope break belts, thick layers of reservoir sands originated from the delta front and gravity flow are developed in the Chang-6 Member in Huaqing, and the favorable sedimentary facies and diagenetic facies control the extensive low-permeability reservoirs. The Chang-6 low-permeability reservoirs and the Chang-7 high-quality source rocks have a good association and form an accumulation mode characterized by “hydrocarbon-generating pressurization, proximal migration and accumulation, large-area charging, and continuous oil layers”.

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Research advances and direction of hydrocarbon accumulation in the superimposed basins, China: Take the Tarim Basin as an example

Pang Xiongqi; Zhou Xinyuan; Yan Shenghua; Wang Zhaoming; Yang Haijun; Jiang Fujie; Shen Weibing and Gao Shuai

, 2012, 39(6): 2086-0.

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The superimposed basins in the Tarim Basin are characterized by multiple source-reservoir-caprock combinations, multiple stages of hydrocarbon generation and expulsion, and multicycle hydrocarbon accumulation. To develop and improve the reservoir forming theory of superimposed basins, this paper summarizes the progress in the study of superimposed basins and predicts its development direction. Four major progresses were made in the superimposed basin study: (1) widely-distributed of complex hydrocarbon reservoirs in superimposed basins were discovered; (2) the genesis models of complex hydrocarbon reservoirs were built; (3) the transformation mechanisms of complex hydrocarbon reservoirs were revealed; (4) the evaluation models for superimposed and transformed complex hydrocarbon reservoirs by tectonic events were proposed. Function elements jointly control the formation and distribution of hydrocarbon reservoirs, and the superimposition and overlapping of structures at later stage lead to the adjustment, transformation and destruction of hydrocarbon reservoirs formed at early stage. The study direction of hydrocarbon accumulation in superimposed basins mainly includes three aspects: (1) the study on modes of controlling reservoir by multiple elements; (2) the study on composite hydrocarbon-accumulation mechanism; (3) the study on hydrocarbon reservoir adjustment and reconstruction mechanism and prediction models, which has more theoretical and practical significance for deep intervals in superimposed basins.

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Formation conditions and exploration potential of tight oil in the Permian saline lacustrine dolomitic rock, Junggar Basin, NW China

Kuang Lichun; Tang Yong; Lei Dewen; Chang Qiusheng; Ouyang Min; Hou Lianhua and Liu Deguang

, 2012, 39(6): 2087-0.

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The features and exploration potential of the Permian tight oil in the Junggar Basin were analyzed and evaluated using outcrop, core and geochemical data etc. The Junggar Basin in the Early-Mid Permian is a saline lacustrine basin after the residual sea is closed, a set of hybrid sedimentation of deep-lake dark mudstone and dolomitic rock is developed, and the high-quality mudstone source rocks and the dolomite mudstone are alternated. High quality source rocks in mature stage are next to tight dolomitic rock reservoirs closely and provide good conditions for tight oil accumulation of proximal source type. Tight oil reservoirs are mainly distributed in the centre and slope region of the lake basin, and two types sweetspots of “dissolved pore” and “fracture-pore” exist locally. The enrichment of tight oil is controlled by the distribution of effective source rocks and dolomitic rocks, and the tight oil occurs in the entire strata vertically and spreads across large continuous areas horizontally. The Junggar Basin has four Permian tight oil distribution areas, Fencheng Formation in the Mahu sag, Lucaogou Formation in the Jimusaer sag, Pidiquan Formation in the Shazhang-Shishugou sag, and Lucaogou Formation in the Bogeda piedmont. A number of wells obtained oil flow in these areas, suggesting great resource potential and favorable targets for future exploration.

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Adjustment and alteration of hydrocarbon reservoirs during the late Himalayan period, Tarim Basin, NW China

Zhang Shuichang; Zhang Bin; Yang Haijun; Zhu Guangyou; Su Jin and Wang Xiaomei

, 2012, 39(6): 2088-0.

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To figure out the oil and gas distribution pattern in the Tarim Basin, the adjustment and reformation of oil and gas reservoirs under the background of late Himalayan Orogeny are analyzed. Strongly affected by the tectonic movement, the oil and gas reservoirs in the Tarim Basin experienced secondary actions in physical adjustment and chemical alteration: on the one hand, during the course of physical adjustment, reversed strata caused the early-formed oil to seep vertically and to migrate laterally along the sandstone in large scale with long distance; on the other hand, in the process of chemical alteration, the deposition of massive strata accelerated the thermal evolution of organic matter, generating large amounts of cracking gas, which went into the pre-existing reservoirs and led to big change in oil and gas properties and the coexistence of heavy oil, light oil, waxy oil and condensate gas in the same area. The physical adjustment and chemical reformation of oil and gas reservoirs in late Himalayan period resulted in the lateral differential distribution of oil and gas in large area and multiple vertical oil-bearing layers with complex and diverse oil and gas properties.

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Stratigraphic division and correlation and sedimentary characteristics of the Cambrian in central-southern Sichuan Basin

Li Wei; Yu Huaqi and Deng Hongbin

, 2012, 39(6): 2089-0.

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Under the guidance of sequence stratigraphy and through analyses of large amounts of well and outcrop data, the correspondence of all formations in the Cambrian of southern and central Sichuan Basin is defined and a new scheme of stratigraphic division and correlation for the Cambrian in central-southern Sichuan Basin is proposed based on the characteristics of lithology, logging curves and fossils. The Jiulaodong Formation in southern Sichuan Basin is corresponding roughly to the Qiongzhusi Formation in central Sichuan Basin, the Yuxiansi Formation in southern Sichuan roughly to the Canglangpu, Longwangmiao and Gaotai formations in central Sichuan Basin, the Xixiangchi Group in southern Sichuan roughly to the same group in central Sichuan. The Cambrian in central-southern Sichuan Basin is divided into the Qiongzhusi Formation, Canglangpu Formation, Longwangmiao Formation, Douposi Formation and Xixiangchi Group from bottom to top. On the basis of that, sedimentary facies of the Cambrian was studied. Controlled and impacted by the paleo-uplifts formed by Caledonian Orogeny, the deposition of the Cambrian experienced three evolutionary stages: shore–continental shelf, restricted platform–evaporation flat–shelf lagoon, restricted platform. The sandy, oolitic and carst dolomites in the Longwangmiao Formation and the Xixiangchi Group are the targets of oil and gas exploration.

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Characteristics of shale lithofacies and reservoir space of the Wufeng–Longmaxi Formation, Sichuan Basin

Liang Chao; Jiang Zaixing; Yang Yiting and Wei Xiaojie

, 2012, 39(6): 2090-0.

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Based on observation of the outcrops and cores of the Late Ordovician to the Early Silurian Wufeng-Longmaxi shale, developed in the deep water shelf environment, in the southeast of the Sichuan Basin, the mineralogical features, lithofacies characteristics and reservoir space types were studied and the factors affecting reservoir capacity were analyzed by observation through eletron microscope and analysis of mineral contant. The mineral composition is dominantly clastic quartz and clay minerals, with feldspar, calcite, dolomite, pyrite and so on. Five lithofacies, i.e. carbonaceous shale, siliceous shale, silty shale, calcareous shale and ordinary shale, were identified in the Wufeng–Longmaxi shale. Seven types of reservoir space, including structural tension fracture, structural shear fracture, interlayer lamellation fracture, pyrite pore, the inter-crystal micro-pore and micro-crack in clay mineral, the edge micro-crack around quartz grains and organic matter pore, were found in the Wufeng–Longmaxi shale. The development of reservoir space is strongly controlled by the mineral composition, lithofacies, organic carbon content, organic matter maturity and diagenesis.

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Formation overpressure and shale oil enrichment in the shale system of Lucaogou Formation, Malang Sag, Santanghu Basin, NW China

Liu Bo; Lü Yanfang; Zhao Rong; Tu Xiaoxian; Guo Xiaobo and Shen Ying

, 2012, 39(6): 2091-0.

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According to observation of cores and thin sections, as well as analyses of fluid pressure features and geochemical indexes, the cause of fluid overpressure and the mechanism of shale oil enrichment in the Lucaogou Formation, Malang Sag, Santanghu Basin, were discussed. The results show that the shale oil of the Lucaogou Formation is generated in the low mature–premature stage of the source rocks and has the features of high density and high viscosity. The low-permeability and thick source rocks lead to high start-up resistance of fluid, which made it difficult for oil and gas to expel, so the retainment of oil and gas in source rocks is the major cause of formation overpressure. Excellent generation potential and well developed reservoir space are the basis for the oil retention; the pressure produced by hydrocarbon generation is not high enough to overcome the resistance of oil migration, which leads to the enrichment of shale oil. The enrichment degree of shale oil is controlled by hydrocarbon generation and storage capacity of lithofacies at various evolution stages.

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Numerical simulation of the dual laterolog response to fractures and caves in fractured-cavernous formation

Deng Shaogui; Mo Xuanxue; Lu Chunli; Zhang Yang and Liu Lailei

, 2012, 39(6): 2092-0.

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To study the response characteristics of dual laterolog in fractured-cavernous reservoirs, a model of fractures and caves was built, and the 3-D finite element method was utilized to simulate its logging responses. Caves of certain size have influence on the response of dual laterolog within certain space. With the cave size increasing, the logging apparent resistivity becomes lower, and the apparent resistivity ratio of deep laterolog to shallow laterolog decreases. Within less than the one-cave radius scope, the dual laterolog is more sensitive to the cave to borehole wall. The logging response of fractured-cavernous formation is mainly affected by fractures, and low angle fractures result in a negative difference of dual laterolog which is contrary to high angle fractures, but the existing caves do not change the matching relationship between the shallow and deep resistivity and fracture dip. The apparent conductivity of dual laterolog in fracture-cave formation presents a linear relationship with fracture aperture.

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Measurement of three-phase relative permeabilities

Lü Weifeng; Liu Qingjie; Zhang Zubo; Ma Desheng; Wu Kangyun and Leng Zhenpeng

, 2012, 39(6): 2093-0.

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Three-phase relative permeabilities of water-wet and oil-wet outcrops with two saturating histories (DDI and IID) are investigated by steady physical simulation experiments. CT Dual Energy Simultaneous Scanning (DESS) method was introduced to measure three-phase saturations accurately, which can eliminate the end effect. The relative permeability of each phase at a given saturation is calculated by Darcy law. The experiment results clearly show that for water-wet cores, the isoperms of water are straight lines, which means that the relative permeability of water depends on water saturation only. The isoperms of oil are curves concave towards 100% oil saturation point, and the isoperms of gas are curves convex towards 100% gas saturation point, which means that the relative permeabilities of oil and gas depend on all the three phase saturations. For oil-wet cores, all the isoperms of water, oil and gas are curves convex towards their 100% saturation points, which means that the relative permeabilities of water, oil and gas depend on all the three phase saturations. In addition, the isoperms of wetting phase are similar for the two saturation histories, while those of non-wetting phases are quite different. Though the isoperms are the same in shape, they are different in values and positions.

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Propagation and control of fire front in the combustion assisted gravity drainage process using horizontal wells

Liang Jinzhong; Guan Wenlong; Jiang Youwei; Xi Changfeng; Wang Bojun and Li Xiaoling

, 2012, 39(6): 2094-0.

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The propagating characteristics of combustion fronts and coke zones in the combustion assisted gravity drainage process were studied using 3D physical simulation experiments. The main mechanisms and factors affecting stable propagation of the combustion fronts were discussed. The experimental results show that the propagation of combustion front can be divided into startup stage, radial expands stage and moving forward stage. The top oil layer is ignited first at the startup stage. Ignition temperature, ignition time and air injection rate are the key parameters for successful ignition. At the radial expanding stage the combustion front grows in size and expands radically and downwards like a funnel, and the air injection rate should match the area of combustion front. After the combustion front propagates beyond the “toe” position, the burning zone would advance along the horizontal well at a certain angle. The controlled gas override and gas seal of the coke in the horizontal well contributes significantly to the overall stability of the process. In field pilot testing, well pattern, ignition parameters and regime of injection and production should be optimized to ensure the stable propagation of the combustion front.

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Production characteristics and affecting factors of high-mid rank coalbed methane wells: Taking Fanzhuang and Hancheng mining areas as examples

Kang Yuanyuan; Shao Xianjie and Wang Caifeng

, 2012, 39(6): 2095-0.

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Production characteristics of coalbed methane wells in Fanzhuang and Hancheng mining areas, which are typical high and mid rank coal fields, are analyzed, compared, and summarized. And the effects of perforating thickness, number of perforated layers, unloading technology and stimulation treatment on gas production are analyzed. Coalbed methane wells in Fanzhuang and Hancheng mining areas are divided into four categories: high gas-production wells, middle gas-production wells, low gas-production wells and little gas-production wells. High gas-production wells have gas production of more than 3 000 m3/d, long stable production period, slow and smooth declining rate, high peak production and short unloading period. Middle gas-production wells have gas production between 1 000 m3/d and 3 000 m3/d, shorter stable production period, longer unloading period and quick declining rate at the early stage. Low gas-production wells have gas production of less than 1 000 m3/d, short stable production period, high water output, long unloading period and discontinuous production. Little gas-production wells have large water output, slow reducing rate of liquid level and a low or zero surface casing pressure. Based on the production characteristics, three types of production modes of coalbed methane wells are summed up. In view of specific examples, it is discussed quantitatively and qualitatively how different factors affect the gas production of coalbed methane wells. It turns out that, generally, the perforating thickness of coalbed methane wells should be larger than 5 m and the layers of perforation should not exceed 3 layers. A proper unloading system is needed to maintain stable and persistent high gas production, and secondary stimulation treatments can bring about significant production increase.

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Classification of the average capillary pressure function and its application in calculating fluid saturation

Hu Yong; Yu Xinghe; Chen Gongyang and Li Shengli

, 2012, 39(6): 2096-0.

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When reservoir heterogeneity is strong, there is a great error between the calculated oil saturation based on the J-function and the actual oil saturation interpreted by logging. Aimed at this problem, a reservoir quality index is proposed to classify the average mercury curves, and the reservoir quality index model and original oil saturation model are established, by experimental measurement and numerical simulation with an illustration of an oilfield in the Pearl River Mouth Basin. The oil saturation calculated with this method accords closely with that interpreted by logging, it is a reliable method to show the properties of strongly heterogeneous reservoirs. In addition, this paper proposes a comprehensive utilization of mercury curve and mercury-ejection curve fitting J-function in establishing the saturation model of bound water, movable water, residual oil, movable oil. Considering the influences of such factors as reservoir quality index and clay content on mercury-ejection efficiency, “mercury-ejection index” is used to classify the average mercury-ejection curves and a movable oil saturation model is established, which provides basis for the calculation of recoverable reserves and the research of residual oil distribution.

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Steam channeling control in the steam flooding of super heavy oil reservoirs, Shengli Oilfield

Cao Yanbin; Liu Dongqing; Zhang Zhongping; Wang Shantang; Wang Quan and Xia Daohong

, 2012, 39(6): 2097-0.

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In view of the severe steam channeling in the steam flooding of super heavy reservoir, lab experiment on steam channeling control were carried out. The combination of nitrogen foam and thermoset blocking agent was tested to seal steam channeling, in which thermoset blocking agent plugs big pore throats, while nitrogen foam adjusts steam absorption profile. The optimized foam formulation has a resistance factor of over 30 at 300 ℃, can plug low oil saturation areas selectively, and applies to the plugging of high permeability zones in super-heavy oil reservoirs. Thermoset blocking agent, which would consolidate at 120 ℃ in 4 h and consolidate at 150 ℃ in 2 h, can provide effective plugging during dynamic steam flooding. The best steam channeling control mode was determined using parallel tube model. By the combination of nitrogen foam and thermoset blocking agent, the recovery rate is 5.7% higher than the application of nitrogen foam only, with the overall sweeping efficiency reaching up to 60.8%. In 2011, the mode was used in the steam flooding in Shan-56 reservoir. The water cut drops 10.2%, the wellhead temperature of producer drops more than 15 ℃, the oil production of the well group increases over 28 tons per day, the valid period of a single cycle is up to 198 days, and the oil production increases 2 562 t, showing significant improvement in steam flooding.

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Physical simulation and fine digital study of thermal foam compound flooding

Pang Zhanxi; Liu Huiqing; Ge Pingyuan and Han Li

, 2012, 39(6): 2098-0.

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According to the similarity criterion of 3D physical simulation of thermal recovery, experimental parameters of 3D physical simulation of steam flooding and thermal foam compound flooding in extra-heavy oil reservoirs of the Gudao Oilfield were calculated, and relevant experiments were carried out. Based on the experimental results, 3D fine numerical simulation was carried out to analyze the steam flooding and thermal foam compound flooding in heavy oil reservoirs. The results show that thermal foam compound flooding could effectively inhibit steam channeling and improve sweep efficiency, and thus enhance the oil recovery in heavy oil reservoirs after steam flooding. Technological parameters of thermal foam compound flooding were optimized according to the results of fine numerical simulation. The optimum injection method is foam-slug injection, the optimal steam injection rate is 25 mL/min, nitrogen injection rate is 1 000 mL/min (standard conditions), the time of foam-slug injection is 1.0 min and the interval between foam-slugs is about 10-20 min during thermal foam-slug injection. At last, the similarity criterion was employed for inversion calculation of the optimization results. Based on the results, optimal field injection and production parameters can be confirmed. The ultimate recovery ratio of thermal foam compound flooding in super-heavy oil reservoirs could reach 42.15%, which is 12.50% higher than steam flooding.

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Extracting pulse signals in measurement while drilling using optimum denoising methods based on the ensemble empirical mode decomposition

Zheng Yi; Sun Xiaofeng; Chen Jian and Yue Jun

, 2012, 39(6): 2099-0.

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To extract original pulse signals in measurement while drilling (MWD), different low-pass filtering methods were designed based on intrinsic mode functions through the ensemble empirical mode decomposition (EEMD). After shaping square waves, a filtering and shaping algorithm on pulse signals was designed. An indgement criterion of filtering algorithms was established according to the degree of approximation and relevance of the algorithm. To simulate pulse signals in measurement while drilling, unit impulse signal, periodic noise signal and Gaussian white noise signal were combined, the denoising effect on the simulating signals was analyzed. The optimum denoising algorithm is composed of the intrinstic mode functions (without the front 4 intrinsic mode functions) and the remainders in EEMD. The degree of approximation of denoising algorithm is 0.771 9 and relevance is as high as 0.892 9. The real-time mud signals of MWD was analyzed and discussed with the help of the algorithm, the results obtained were reasonable and effective.

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Performance evaluation for littoral-facies clastic reservoir architecture

Long Ming; Xu Huaimin; Jiang Tongwen; Niu Yujie; Xu Zhaohui and Chen Yukun

, 2012, 39(6): 2100-0.

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Taking the littoral-facies clastic reservoir of Donghe sandstone in HD4 oil field, Tarim Basin, NW China as an example, this paper analyzes the effect of different reservoir architecture pattern on oil well production performance. There are three types of reservoir architecture patterns in the target layers of the study area, parallel, groove and oblique. The dynamic response characteristics of different reservoir architecture patterns were discussed by establishing the conceptual model of different reservoir architecture patterns, in conjunction with numerical reservoir simulation results and actual production performance of the study area. Based on the numerical simulation, together with analysis of geologic factors and performance evaluation, a performance evaluation method for clastic reservoir architecture of littoral facies was put forward, in turn, the distribution scopes of different reservoir architecture patterns in the study area were identified by this method. The research results show that the parallel reservoir architecture only affects oil well production in vertical direction, the oblique reservoir architecture has the strongest effect on oil well production performance, reflected in both vertical and lateral direction, the effect of groove reservoir architecture on oil well production is mainly in vertical direction, relatively weak in lateral direction. Different adjustment measures should be adopted for the distribution areas of different reservoir architecture patterns.

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Experiments on the gas production of brown coal degraded by exogenous methanogens

Wang Han; Lin Hai; Dong Yingbo; Sui Mengqi and Li Yangzi

, 2012, 39(6): 2101-0.

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To investigate the ability of exogenous bacteria to degrade brown coal, methanogens were enriched from anaerobic sludge and domesticated using brown coal as the single carbon source. After domestication, the lag time of initial gas production is shortened from 12 to 6 days and the CH4 production increases by 29.2% in 30 days. The generated biogas is composed of CH4 and a little CO2, no heavy hydrocarbons are detected. Experiments on gas production influencing factors demonstrate that the best initial pH for the culture medium is 7.0 and the maximum gas production is 1.9 times and 2.4 times higher than that at pH 6.4 and pH 7.4, respectively. The particle size of coal is one of factors influencing the gas production: the general trend is the smaller the particle size, the bigger the gas production, but the variation of gas production is not significant with decreasing particle size. Gas produced by the culture medium accounts for around 50% of the total gas production and it is likely caused by the addition of L-cysteine (0.5 g/L) and yeast extract (1 g/L) to the medium.

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, Volume 39 Issue 6