New insights into the carbonate karstic fault system and reservoir formation in the Southern Tahe area of the Tarim Basin |
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| Institution: | 1. Northwest Oilfield Company, SINOPEC, Urumuqi, Xinjiang, 830011, China;2. Petroleum Exploration & Production Research Institute of Northwest Oilfield Company, SINOPEC, Urumuqi, Xinjiang, 830011, China;3. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;1. College of Energy, Chengdu University of Technology, Chengdu, Sichuan 610059, China;2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, PR China;2. China University of Petroleum, Beijing 102249, PR China;3. China National Petroleum Corporation, Beijing 100007, PR China;4. Oil and Gas Exploration and Development Institute of Tarim Oilfield, Korla 841000, PR China;1. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing, 100083, China;2. Center of Journals & Annals, Hebei GEO University, Shijiazhuang, 050031, China;3. China Petroleum & Chemical Corporation, Beijing, 100728, China;4. Oil & Gas Survey, China Geological Survey, Beijing, 100083, China;5. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing, 100081, China;1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;2. School of Geosciences, China University of Petroleum, Qingdao, 266580, China;3. Tahe Oilfield Branch Company, SINOPEC, Urumqi, 830011, China;4. Petroleum Exploration & Production Research Institute, SINOPEC, Beijing, 100083, China |
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| Abstract: | As worldwide hydrocarbon exploration has extended from shallowly to deeply buried strata, reservoir quality has attracted substantial and persistent interest in petroleum geology. In particular, deeply buried strata (>5500 m) in the Tarim Basin have attracted considerable attention because carbonate reservoirs that have experienced fracture or dissolution have also been shown to demonstrate considerable hydrocarbon potential. Therefore, it is necessary to determine how these reservoirs are developed and distributed in detail from both scientific and practical standpoints.In this paper, we address this issue using a case study in the southern Tahe area, which is contained within the largest Palaeozoic marine oilfield in China. In the northern Tahe area, mega-paleokarst systems developed in the Ordovician strata; however, the reservoir quality in the southern part of the Tahe area is relatively poor because it is covered by insoluble formations during karstification. Observations of cores and analyses of images of well logging demonstrate that these reservoirs are dominated by caves, vugs and fractures that have developed near faults. We speculate that the faults penetrating insoluble formations represent the main dissolution passages that originally developed these karstic fault systems. Additionally, we analyse a series of outcrops, seismic data, and structures to characterize the spatial geometry of these major faults and their surrounding fractures in detail. Most of these are strike-slip faults, and their subsequent reservoirs can be divided into three categories based on their development, including dendritic, sandwich and slab reservoirs. Recent studies demonstrate that karstic fault reservoirs are most common traps in the study area. Although various types of carbonate karstic fault reservoirs are represented in this region, the dendritic karstic fault reservoir is the most hydrocarbon-rich.Guided by these initial results, 108 wells were drilled from 2013 to 2014, producing 485 thousand tons of oil and yielding success ratios greater than 89%. The average production of dendritic reservoirs is 37.4 tons per day (t/d), while those of sandwich and slab types are 20.2 t/d and 14.0 t/d, respectively. These results represent significant references for future hydrocarbon exploration and the development of similar deeply buried karstic fault reservoirs in the Tarim Basin and elsewhere. |
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| Keywords: | Karstic fault system Fault damage zones Paleokarst reservoir Reservoir types Tarim basin |
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