Geological roles of the siltstones in tight oil play |
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| Institution: | 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, 102249, China;2. College of Geosciences, China University of Petroleum, Beijing, 102249, China;3. Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843-3115, USA;4. Songyuan Gas Production Plant in Jilin Oilfield Company, PetroChina, Songyuan, 138000, China;5. PetroChina Xinjiang Oilfield Company, Karamay, 834000, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;2. CNOOC Research Institute, Beijing 100027, China;1. College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao, 266590, Shandong, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, China;3. Department of Geology, University of Pretoria, Private Bag X20, 0028, Pretoria, South Africa;4. Institute of Exploration and Development, Changqing Oilfield Company, Petrochina, Xi''an, 710069, Shaanxi, China;1. School of Environmental Studies, China University of Geosciences, Wuhan, Hubei 430074, PR China;2. Department of Geology and Geophysics, Texas A& M University, College Station, TX 77843-3115, USA;1. Guangzhou Marine Geological Survey, China Geological Survey, Ministry of Natural Resources, Guangzhou 510075, China;2. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China;3. School of Geosciences, China University of Petroleum, Qingdao 266580, China;4. Sinopec Northeast Oil-Gas Branch Company, Changchun 130062, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, 102249, China;2. College of Geosciences, China University of Petroleum, Beijing, 102249, China;3. Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843-3115, USA;4. PetroChina Xinjiang Oilfield Company, Karamay, 834000, China;5. Tianjin Branch Company, China Offshore Petroleum Corporation, Tianjin, 300452, China;1. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu 210023, PR China;2. PetroChina Xinjiang Oilfield Company, Karamay, 834000, PR China |
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| Abstract: | Understanding the hydrocarbon accumulation pattern in unconventional tight reservoirs is crucial for hydrocarbon evaluation and oil/gas extraction from such reservoirs. Previous studies on tight oil accumulation are mostly concerned with self-generation or from source to reservoir rock over short distances. However, the Lucaogou tight oil in Jimusar Sag of Junggar Basin shows transitional feature in between. The Lucaogou Formation comprises fine-grain sedimentary rocks characterized by thin laminations and frequently alternating beds. The Lucaogou tight silt/fine sandstones are poorly sorted. Dissolved pores are the primary pore spaces, with average porosity of 9.20%. Although the TOC of most silt/fine sandstones after Soxhlet extraction is lower than that before extraction, they show that the Lucaogou siltstones in the area of study have fair to good hydrocarbon generation potential (average TOC of 1.19%, average S2 of 4.33 mg/g), while fine sandstones are relatively weak in terms of hydrocarbon generation (average TOC of 0.4%, average S2 of 0.78 mg/g). The hydrocarbon generation amount of siltstones, which was calculated according to basin modeling transformation ratio combined with original TOC based on source rock parameters, occupies 16%–72% of oil retention amount. Although siltstones cannot produce the entire oil reserve, they certainly provide part of them. Grain size is negatively correlated with organic matter content in the Lucaogou silt/fine sandstones. Fine grain sediments are characterized by lower deposition rate, stronger adsorption capacity and oxidation resistance, which are favorable for formation of high quality source rocks. Low energy depositional environment is the primary reason for the formation of siltstones containing organic matter. Positive correlation between organic matter content and clay content in Lucaogou siltstones supports this view point. Lucaogou siltstones appear to be effective reservoir rocks due to there relatively high porosity, and also act as source rocks due to the fair to good hydrocarbon generation capability. |
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| Keywords: | Tight oil accumulation Tight siltstone Hydrocarbon generation quantity Storage capacity |
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