, Volume 38 Issue 4

    

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油气勘探
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  Assessment on gas accumulation potential and favorable plays within the Xu-1, 3 and 5 Members of Xujiahe Formation in Sichuan Basin

  Zhao Wenzhi; Bian Congsheng; Xu Chunchun; Wang Hongjun; Wang Tongshan and Shi Zhensheng

  . 2011, 38(4): 2-0.

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  Natural gas exploration and discovery in the Sichuan Basin are mainly concentrated in the Xu-2, 4 and 6 Members of the Xujiahe Formation. The discovered gas reservoirs are characterized by low degree of fullness, high water saturation in lower positions, low level of produced reserves, and limited gas bearing range of reservoirs. The Xu-1, 3 and 5 Members are identified as source rocks. Based on the study of natural gas accumulation conditions and several gas-productive wells in the Xu-1, 3 and 5, this paper proposes that large scale sand bodies are recognized in the Xu-1, 3 and 5 Members in the northwest, southwest and central parts of the Sichuan Basin. In each member, the favorable gas bearing area is about 5 000–11 000 km2, reservoir rocks have good continuity with single layer extension up to 15–20 km. It is believed that these sand bodies have favorable conditions for gas accumulation within source kitchens to form lithologic or structural-lithologic gas reservoirs, and have better accumulation potential and higher gas-bearing abundance than that of the Xu-2, 4 and 6 Members. The exploration practice revealed that economic gas reserves might be generated. It is suggested that more efforts be made to study the gas accumulation conditions in the Xu-1, 3 and 5 Members (especially the Xu-3 and Xu-5 Members) and more exploration work be fulfilled in these strata.
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  Fracture characteristics and genetic mechanism of overpressure carbonate reservoirs: Taking the Kenjiyak Oilfield in Kazakhstan as an example

  Bian Dezhi; Zhao Lun; Chen Yefei; Yu Lian and Fan Zifei

  . 2011, 38(4): 2-0.

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  Taking the Kenjiyak Oilfield in Kazakhstan as an example, the fracture characteristics and genetic mechanism of carbonate reservoirs with overpressure were discussed. The study showed that: carbonate reservoirs formed under overpressure developed hydraulic fractures besides tectonic fractures and karstic fractures. The Carboniferous sub-salt hydraulic fractures in Kenkiyak mainly formed in the Mesozoic and Cenozoic, on a macroscopic level they cut rocks into brecciated texture or are packed by calcite veins, on a microscopic level they are in a radiant distribution around pores. The formation and evolution of the fracture system in the region experienced three main stages, including structure transforming and uplifting, structure stretching and subsiding, and hydraulic cracking. In the stage of hydraulic cracking, salt movement and tectonic movement lead to the formation of overpressure zone, with the pressure coefficient of 1.84. Overpressure leads to the formation of hydraulic fractures in the Carboniferous low permeable carbonate reservoirs under the Permian non-permeable mudstones, and also leads to reopening, widening and prolonging of former tectonic fractures. Hydraulic fractures are mainly the extensional fracture, which has late opening time and low filling degree, thus is the main effective fractures in the study area.
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  Depositional systems and evolution of Upper Carboniferous Huanglong Formation in the eastern Sichuan Basin

  Li Wei; Zhang Zhijie and Dang Lurui

  . 2011, 38(4): 2-0.

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  Carboniferous reservoirs are the main gas producing formation in the Sichuan Basin. New research on basic geology has been done for Upper Carboniferous carbonate lithologic gas pools in the Huanglong Formation of in the eastern Sichuan Basin. Based on the development characteristics of terrigenous clastic deposit and the development location of suspending gravels with some psephicity, the transgression direction and tidal depositional system distribution are deduced. It is believed that, two transgression channels developed in southeast of Yunyang and northwest of Dazhou in the area, two tidal-flat depositional systems in Chongqing-Wanzhou and southeast of Dazhou respectively were formed, and a suit of complete type-I sequence composed of lowstand systems tract (C2h1), transgressive systems tract (C2h2) and early highstand systems tract (C2h3) was developed. Sedimentary microfacies features of each member of the Huanglong Formation were delineated finely. In the middle stage of late Carboniferous in eastern Sichuan, transgressive systems tract was developed, where shallow beach and algal dolomite-flat microfacies were developed, which are favorable for the development of carbonate lithologic traps. In contrast, in the early and late stages of late Carboniferous, lowstand systems tract and highstand systems tract were developed, respectively, where shallow beach microfacies were not developed, which limited the large scale development of carbonate lithologic traps.
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  Modeling of the tight sandstone gas accumulation for the Xujiahe Formation, Hechuan-Tongnan Area, Sichuan Basin

  Guo Qiulin; Li Jianzhong; Chen Ningsheng; Hu Junwen; Xie Hongbing and Gao Xiaohui

  . 2011, 38(4): 2-0.

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  The tight sandstone gas accumulation is mainly driven by overpressure arising from gas generation in source rocks. This paper proposes a quantitative computation model for pressurization from gas generation in source rocks, establishes a dynamic equilibrium equation and a modeling process for tight sandstone gas accumulation, and simulates the gas generation quantity and source rock overpressure history in the Hechuan-Tongnan area of the Sichuan Basin. The modeling reveals that: (1) The gas generation intensity determines the degree of pressurization from gas generation, whereas the reservoir property determines the distribution of gas reservoirs; the conventional gas reservoir is complementary with the tight sandstone gas reservoir in terms of horizontal and vertical distribution, the former is mainly distributed at the top of reservoir with porosity over 7% on local structural highs while the latter is mainly distributed at the bottom of reservoir on local structural lows near source rocks of large gas generation quantity. (2) During the uplifting process from the maximum burial depth (65 Ma) to the current burial depth (0Ma), because of the pressure drop of formation water and the increase of gas-water pressure difference, the tight sandstone gas migrates farther and increases in accumulation quantity; however, the conventional gas does not migrate basically and has no increase in accumulation quantity; (3) The quantity of the tight sandstone gas in the T3x2 Layer is 5.9 times that of the conventional gas, and the undiscovered resource is mainly tight sandstone gas distributed in northeast of Hechuan, and north and southeast of Tongnan.
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  Carbon isotopic compositions of coal-formed gas in the Xujiahe Formation and Jurassic in western Sichuan Basin

  Wu Xiaoqi; Huang Shipeng; Liao Fengrong and Li Zhensheng

  . 2011, 38(4): 2-0.

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  Coal-measure source rocks in the Sichuan Basin are important gas-source rocks, and provide sufficient natural gas for self-generation and self-storage gas reservoirs in the Xujiahe Formation and secondary gas reservoirs in the overlying Jurassic. The gas reservoirs in the Xujiahe Formation are mainly located in western and central Sichuan gas provinces, while those in the Jurassic in western Sichuan gas province. Natural gas derived from coal measures source rocks in the Xujiahe Formation are typical thermogenic gas and shares the same characteristics of humic type gas. The carbon isotopic characteristics of gas samples in the Jurassic are generally identical to those in the Xujiahe Formation. The carbon isotopic compositions of the coal-formed gas tend to become lighter from bottom to top in the Xujiahe Formation. The gases in the Jurassic have no clear rule due to their coming from different members of the Xujiahe Formation, and they tend to accumulate near the source. Horizontally, the δ13C values of alkane gas from the southern part of the western Sichuan gas province are heavier than those from the northern part, while both are obviously greater than those in the central and southern Sichuan gas provinces. Several gas samples in the Xujiahe Formation and Jurassic are characterized by partially reversed carbon isotopic series, mainly due to the influence of mixing of gas from the same source but different periods. The mixing of oil-type gas not only reduces the δ13C values of several coal-formed gas samples in the central Sichuan gas province, but also causes the partial reversal of carbon isotopic series of some gas samples.
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  General characteristics and meanings of burial dissolution of Lower-Palaeozoic dolomite reservoirs in eastern Tarim Basin

  Jin Zhenkui and Yu Kuanhong

  . 2011, 38(4): 2-0.

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  Based on the characteristics of core, thin-section, physical properties and oxygen and strontium isotope, the characteristics of Lower Paleozoic dolomite reservoirs, dissolution features and mechanism in eastern Tarim Basin were studied. Massive dissolution pore-cave dolomite is the main reservoir type in eastern Tarim Basin. The dissolution pores and caves are mainly medium to small with dense distribution. The fillings in dissolution pores and cracks commonly show negative δ18O, generally far lower than the surrounding rock; slightly negative δ13C, partially positive; slightly high 87Sr/86Sr. Proportion of CH4 and CO2 is high in fluid inclusions and some of them contain high proportion of H2S, which demonstrated that, in deep burial circumstances, evolution of organic matter was at the high evolution stage. Silicification and highly homogeneous temperature also indicate the presence of hydrothermal fluids. Dissolution includes organic acid dissolution and hydrothermal water dissolution. Acid fluid mainly includes organic acid, CO2 and H2S, which mainly generated in the process of evolution of organic matter, with little H2S from sulfate reduction, a little CO2 from volcanic activity. As carrier of acid fluid, hydrothermal fluid overcomes kinetic obstruction of dissolution and dissolves the deep dolomite. Major faults and associated faults provide channels for hydrothermal fluids, which further disperse in dolomites through numerous inter-crystal pores caused by dolomitization and micro-cracks caused by compaction to complete dissolution for dolomite reservoirs.
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  Distribution of favorable lacustrine carbonate reservoirs: A case from the Upper Es4 of Zhanhua Sag, Bohai Bay Basin

  Peng Chuansheng

  . 2011, 38(4): 2-0.

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  Based on the core thin sections，logging and seismic data, the distribution of favorable lacustrine carbonate reservoirs is predicted in the upper Es4 of Zhanhua Sag of Bohai Bay Basin. In the upper Es4 of Zhanhua Sag, four categories of carbonates are developed i.e. bioclastic limestones (dolomites), intraclastic limestones (dolomites), arenaceous limestones (dolomites) and argillaceous limestones (dolomites). With core’s scale logging, electrical characteristics interpretation criteria for various carbonates are established, and lithofacies sequences of exploratory well are reconstructed. According to overlying pattern of high-frequency cycles, short-term cycles of bioherm, carbonate bank and semi-deep lake are divided, and high resolution isochronous formation framework is built. On the basis of the facies characteristics of well tie sections and palaeo-landform background, carbonate depositional model is established. Namely, reef and bank carbonatite are deposited from the largest expansion period to secular depression period of lake basin, bank carbonates are mainly distributed on the upper side of syndepositional fault on mild slope or deposited in fault-step lowland on steep slope while reef carbonates mainly on fault-step highland on steep slope. Favorable reservoir types include reef bioclastic limestone (dolomite), bank bioclastic limestone (dolomite), intraclastic limestone (dolomite) and arenaceous limestone. It is possible to predict the distribution of favorable reservoirs according to the depositional model, palaeo-landform analysis and seismic amplitude attributes.
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  Application of electrical image logging in the study of sedimentary characteristics in sandy conglomerates

  Yan Jianping; Cai Jingong; Zhao Minghai; Li Zunzhi and Xu Guanhua

  . 2011, 38(4): 2-0.

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  The northern steep-slope region in the Dongying Sag developed sandy conglomerate reservoirs of various origins. However, it is difficult to identify lithology and sedimentary microfacies using conventional logs owing to complex provenance and sedimentary process. The selected research object is the upper Es4 sandy conglomerate reservoir of the Yanjia Oilfield. By use of core and FMI data, the FMI image features of lithology, sedimentary structure and rhythm of different sandy conglomerates are analyzed, and an image of geologic significance is obtained. Then combining with conventional logging, borehole log, and PVT data, the sedimentary cycle and sedimentary facies of single well sandy conglomerate bodies are divided, and the plane distribution of sedimentary facies of sandy conglomerate bodies is concluded, which provides a basis for mapping sedimentary facies and searching for favorable hydrocarbon zones in the study area.
油气田开发
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  Fire-flooding technologies in post-steam-injected heavy oil reservoirs

  Guan Wenlong; Xi Changfeng; Chen Yaping; Zhang Xia; Muhetar; Liang Jinzhong; Huang Jihong and Wu Jian

  . 2011, 38(4): 2-0.

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  The mechanism and problems associated with development engineering of fire-flooding in post-steam-injected heavy oil reservoirs was studied using 1D&3D physical simulation experiments and reservoir numerical simulation. The temperature of combustion zone decreased and high-temperature zone enlarged because there existed secondary water formed during steam injection which could absorb and carry heat towards producers out of combustion front during fire flooding, but high saturation of water in layer caused by secondary water had less influence on the quantity of fuel deposit and air consumption. In the process of 3D fire flooding experiment, air override was observed during combustion front moving forward and resulted in a coke zone in the bottom of layer, and the ultimate recovery factor reached 65% on fact that the remaining oil saturation within the coke zone was no more than 20%. The flooding model, well pattern, well spacing, and air injection rate were optimized according to the specific property and the existed well pattern in the post-steam-injected heavy oil reservoir, and the key techniques of ignition, lifting, and anticorrosion was also selected in the same time. The pilot of fire flooding in the H1 block in the Xinjiang Oilfield was carried out last year based on these research works, and now begins to show better performance.
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  Fire-flooding technologies in post-steam-injected heavy oil reservoirs

  Guan Wenlong; Xi Changfeng; Chen Yaping; Zhang Xia; Muhetar; Liang Jinzhong; Huang Jihong and Wu Jian

  . 2011, 38(4): 2-0.

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  The mechanism and problems associated with development engineering of fire-flooding in post-steam-injected heavy oil reservoirs was studied using 1D&3D physical simulation experiments and reservoir numerical simulation. The temperature of combustion zone decreased and high-temperature zone enlarged because there existed secondary water formed during steam injection which could absorb and carry heat towards producers out of combustion front during fire flooding, but high saturation of water in layer caused by secondary water had less influence on the quantity of fuel deposit and air consumption. In the process of 3D fire flooding experiment, air override was observed during combustion front moving forward and resulted in a coke zone in the bottom of layer, and the ultimate recovery factor reached 65% on fact that the remaining oil saturation within the coke zone was no more than 20%. The flooding model, well pattern, well spacing, and air injection rate were optimized according to the specific property and the existed well pattern in the post-steam-injected heavy oil reservoir, and the key techniques of ignition, lifting, and anticorrosion was also selected in the same time. The pilot of fire flooding in the H1 block in the Xinjiang Oilfield was carried out last year based on these research works, and now begins to show better performance.
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  Grey decision-making theory in the optimization of strata series recombination programs of high water-cut oilfields

  Li Qiaoyun; Zhang Jiqun; Deng Baorong; Chang Junhua; Li Hua; Liu Shuangshuang and Xu Xiaoming

  . 2011, 38(4): 2-0.

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  The development performance of bedded sandstone reservoirs by water drive become worse year by year after entering the high water-cut stage. Optimization and recombination of the strata series based on reservoir subdivision is an effective way to improve water injection effect and to increase producing level. This paper uses the mono-objective grey situation decision-making method, combines various indexes and the expert experiences reflecting reservoir development performance, introduces the concept of effect factors to consider various factors which reflect the contradictories of reservoir strata series, such as permeability differentials, single layer water flooding degree, producing level, remaining amount of resources, hole interval length and the amount of oil layer etc., to create measurement matrix for comprehensive effects and then to work out the optimal solution of strata recombination programs. Case analysis and comparison with the reservoir numerical simulation result showed that, the grey decision-making optimization method has reliable results, can effectively solve the contradiction between traditional method efficiency and effect, and can help to guide the development and adjustment of bedded sandstone reservoirs by water drive during the high water-cut stage.
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  DEM mathematical model of sand-carrying cold heavy oil production

  Wang Bojun; Zhang Xia; Ma Desheng; Fan Jianping; Wang Fenggang and Liang Jinzhong

  . 2011, 38(4): 2-0.

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  The sand production in unconsolidated sandstone reservoirs is essentially caused by erosion and migration of sandstone particles. Due to the complexity of conventional physical modeling and the insufficient modeling capability of current numerical simulation for discontinuous media, this paper established the mathematical model for the Cold Heavy Oil Production (CHOP) procedure considering fluid-solid couplings by using Discrete Element Method, selected the Mohr-Coulomb yield criterion as the failure criterion of particle peeling from parent rock, and described the sand production microscopic mechanism quantitatively. This 1D numerical model presented very good matches with the physical modeling lab results in the simulation of sand production rate, oil production rate and bottom-hole pressure, which verified the proposed mathematical model. Based on this model, the authors also investigated the critical condition of CHOP and wormhole extension rule. By applying the mathematical model into field cases, the calculation results indicate that the discrete element mathematical model can simulate the sand production mechanism in CHOP procedure very well, which provides a new approach to study sand-carrying cold production.
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  Architecture and remaining oil distribution of the sandy braided river reservoir in the Gaoshangpu Oilfield

  Li Shunming; Song Xinmin; Jiang Youwei; Liu Lang; Chen Nengxue; Sun Jingmin and Li Benwei

  . 2011, 38(4): 2-0.

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  With mudstone deposited in flooding period as the marker horizon and based on fine correlation for reservoir genesis, the stratigraphic framework in braided river single sand bed of the lower member of the Neogene Guantao Formation in the Gaoshangpu Oilfield of the Nanpu Sag is established. Guided by braided river geologic outcrops and sedimentary simulation results, based on identification of braided river single river channel, rules of geostatistics and production monitoring data analysis, the width of braided river single river channel in this area is determined as 140-560 m. According to the analysis on lithofacies associations and features of base and top surfaces, 5 architectural elements for braided river reservoirs are identified, i.e. channel filling, downstream accretion, sandy bed form, sand sheet and overbank fines. For channel filling architectural element, lithofacies association of Se-St-Sh-Sm in normal rhythm is developed, with large vertical permeability difference and high oil-water viscosity ratio. Dominant flow pathways emerge at high fluid production rate. Due to high fluid production rate and dominant flow pathways, water coning flooded oil zone will be generated in channel element, which leads to high abundance oil remaining between wells. The downstream accretion element is featured by small vertical permeability difference and uniform water flooding, so thin-layered remaining oil distributes between oil wells with low abundance.
石油工程
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  Application of PCP anti-scaling technology in ASP flooding in the Daqing Oilfield

  Liang Yaning; Cao Gang; Shi Guochen; Wang Guoqing; Li Jinling and Zhao Yunlong

  . 2011, 38(4): 2-0.

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  To solve the severe PCP scaling during ASP flooding in the Daqing Oilfield, PCP anti-scaling and lifting techniques are studied. This paper analyzed the reasons and principles of PCP scaling during ASP flooding were comprehensively, and the common failure mode in PCP wells by scaling. The fit accuracy between PCP’s rotor and stator dropping, frictional behavior irregular changing and severe abrading by scaling are the main reasons for the increase of the PCP’s failures. Based on these, a comprehensive anti-scaling lift technique for PCP wells was proposed including PCP rotor/stator wring optimization, instrument material surface modification, and chemical clear/anti-scaling technique. By the end of 2010, the comprehensive methodology has been applied in 216 PCP producers 425 times, the average running lives of PCP producers in ASP flooding were improved from less than 100 days to 298 days after applying the above PCP anti-scaling methodology, the most longest one is 1370 days.
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  A novel drilling fluid with less free water

  Zhang Yan; Xiang Xingjin; Yan Jienian and Wu Bin

  . 2011, 38(4): 2-0.

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  Through research on the flowing state of free water in drilling fluids, a special complexing agent has been developed. This additive can increase the capillary force for free water to invade reservoirs and thus control filtrate invasion by effectively complexing the free water in drilling fluids. The invasion quantity and invasion depth of water into reservoirs will be reduced. In addition, the complexed free water can form a kind of special micelle and low-pemeability membrane so that it can effectively plug pore throats and microfractures, increase the bearing pressure of formations and decrease the required density of drilling fluids. Based on the results of CST tests, spontaneous water imbibition test of cores and measurement of free water content, it is concluded that the newly formulated drilling fluid with less free water can effectively complex free water in drilling fluids and reduce liquid invasion to formations. Field application shows that the less free water drilling fluid has good behaviors of rheology, lubricity and inhibition. It can increase the bearing capability of the formation, decrease the required density of drilling fluid, and shortens the drilling time.
综合研究
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  Dissolution kinetics of different types of oolitic limestones in northeastern Sichuan Basin

  Wang Wei; Huang Kangjun; Bao Zhengyu and Qian Yixiong

  . 2011, 38(4): 2-0.

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  The oolitic limestone is the target oil and gas reservoir in the northeastern Sichuan Basin, China. The dissolution kinetics experiment method was applied to study the development and evolution rule of hydrocarbon accumulation spaces such as pores, caves and fractures in oolitic limestones. The experiments and micro-morphology observations under different temperatures and pCO2 show that, when pCO2 is 1-4 MPa, at constant temperature, oolitic limestone dissolution rates increase with pressure increasing, and oolitic limestone dissolution rate is greater than dolomitize oolitic limestone; when temperature increases from 25℃ to 150 ℃ and pCO2 is 3MPa, there is weak - strong - weak trends for oolitic limestone dissolution, and the maximum rate occurs at 100 ℃ or so, but dolomitize oolitic limestone’s dissolution rate increases with temperature increasing, higher than non-dolomite oolitic limestone; SEM images show, in addition to the primary structure cracks, the dolomitization oolitic limestone is easier to form micropores such as intergranular pores and intragranular pores than the non-dolomite limestone, indicating that dissolution is not the only controlling factor for oolitic reservoir formation in deep burial environment, and the combination of dolomitization and dissolution is easier to form high-quality reservoirs.
学术讨论
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  The oldest Oil accumulation in China: Neoproterozoic Xiamaling Formation bituminous sandstone reservoirs

  Liu Yan; Zhong Ningning; Tian Yongjing; Qi Wen and Mu Guoyan

  . 2011, 38(4): 2-0.

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  Based on analysis on the coexistent relationship between igneous rock intrusion and bituminous sandstone of the Xiamaling Formation, northern Hebei (qnx), the accumulation time of the Xiamaling Formation bituminous sandstone reservoirs is defined by the methods of organic petrology and isotope chronology. According to field investigation, observation of thin-section and the shallow drilling show, and based on the previous results of oil seepages and bitumen spots in the qnx base sandstone, 31 new oil seepages (bitumen spots) including 21 visible black bitumen spots were discovered in the qnx,. The distribution of paleo-reservoir in the qnx bituminous sandstone was identified, and 4 paleo-reservoirs i.e. Shuangdong paleo-reservoir in Pingquan, Longtangou paleo-reservoir in Lingyuan, Lujiazhuang paleo-reservoir and Tashan paleo-reservoir in Kuancheng, have been named. The reserves of the paleo-reservoirs are 0.7–1 billion tons, which are calculated by volume method with the solid bitumen content. Organic petrology analysis shows that two kinds of solid bitumen with diferent reflectivity characteristics were developed. Class structure of natural coke is discovered in solid bitumen, which is the first direct evidence to prove that severe thermal alteration occurs in the qnx base sandstone bitumen. The age of qnx gabbro-diabase baddeleyite by SHRIMP U-Pb dating method is 1 327 Ma±2 Ma，which indicates that the accumulation time of the Xiamaling Formation bituminous sandstone was 1 400 Ma to 1 327 Ma. So, it is the oldest oil accumulation in China.