Influence of detrital composition on the diagenetic history of tight sandstones with implications for reservoir quality: Examples from the Permian Xiashihezi Formation and Carboniferous Taiyuan Formation,Daniudi gas field,Ordos Basin,China |
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| Institution: | 1. School of Geosciences, China University of Petroleum, Qingdao, 266580, China;2. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States;3. Postdoctoral Scientic Research Working Station of Sinopec Shengli Oilfield Company, Dongying, 257000, China;4. Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, United States;1. School of Energy Resources, China University of Geosciences, Beijing 100083, PR China;2. Coal Reservoir Laboratory of National Engineering Research Center of Coalbed Methane Development & Utilization, Beijing 100083, PR China;3. China United Coalbed Methane Corporation, Ltd., Beijing 100011, PR China;1. School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China;2. College of Geosciences, China University of Petroleum, Beijing 102249, China;3. Research Institute of Petroleum Exploration &Development, PetroChina Changqing Oilfield Company, Xi''an 710018, China;4. Chengdu North Petroleum Exploration & Development Technology Company Limited, China ZhenHua Oil Co., Ltd, Chengdu 610500, China;1. College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing, 100083, China;2. School of Energy Resources, China University of Geoscience, Beijing, 100083, China;3. China United Coalbed Methane Co. Ltd, Beijing, 100011, China;1. MOE Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China;2. State Key Laboratory for Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;3. Langfang Branch of Research Institute of Petroleum Exploration & Development, PetroChina, Langfang, Hebei 065007, China;1. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, Jiangsu, 210023, PR China;2. Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology, Qingdao, Shandong, 266590, PR China;3. Central Sichuan Oil & Gas Field, PetroChina Southwest Oil and Gasfield Company, China National Petroleum Corporation, Suining, Sichuan, 62900, PR China |
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| Abstract: | Tight-gas reservoirs, characterized by low porosity and low permeability, are widely considered to be the product of post-depositional, diagenetic processes associated with progressive burial. This study utilizes a combination of thin section petrography, scanning electron microscopy, microprobe and back scatter electron analysis, stable isotope geochemistry and fluid inclusion analysis to compare the diagenetic history, including porosity formation, within sandstones of the second member of Carboniferous Taiyuan Formation (C3t2) and the first member of Permian Xiashihezi Formation (P1x1) in the Ordos Basin in central China.In the P1x1 member, relatively high abundances of metamorphic rock fragments coupled with a braided river and lacustrine delta environment of deposition, produced more smectite for transformation to illite (50–120 °C). This reaction was driven by dissolution of unstable minerals (K-feldspar and rock fragments) during the early to middle stages of mesodiagenesis and consumed all K-feldspar. Abundant intragranular porosity (average values of 2.8%) and microporosity in kaolinite (average values of 1.5%) formed at these burial depths with chlorite and calcite developed as by-products.In the C3t2 member, relatively low abundances of metamorphic rock fragments coupled with an incised valley-coastal plain environment of deposition resulted in less smectite for transformation to illite. High K+/H+ ratios in the early pore waters related to a marine sedimentary environment of deposition promoted this reaction. Under these conditions, K-feldspar was partially preserved. During the middle to late stages of mesodiagenesis, K-feldspar breakdown produced secondary intragranular (average values of 1.4%) and intergranular pores (average values of 1.2%). Release of K+ ions promoted illitization of kaolinite with quartz overgrowths and ferrous carbonates developed as by-products.This study has demonstrated that whereas both members are typical tight-gas sandstones, they are characterized by quite different diagenetic histories controlled by the primary detrital composition, especially during mesodiagenesis. Types of secondary porosity vary between the two members and developed at different stages of progressive burial. The content of unstable detrital components, notably feldspar, was the key factor that determined the abundance of secondary porosity. |
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| Keywords: | Ordos basin Upper Paleozoic Tight gas sandstones Diagenesis Secondary pores K-feldspar dissolution Illitization |
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