Reservoir characterization of the Pennsylvanian Caddo Limestone in Stephens County,Texas: A case study of Komia-dominated algal mounds |
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| Affiliation: | 1. Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78713, USA;2. BASA Resources Inc., Dallas, TX, USA;1. Statoil, Arkitekt Ebbelsvei, No-7053, Ranheim, Norway;2. Statoil, Strandvegen 4, 7500 Stjørdal, Norway;1. China University of Geosciences, Beijing, China;2. Tianjin Branch of China National Offshore Oil Company Ltd, Tianjin 300452, China;3. Jidong Oilfield, PetroChina, China;4. ESSCA Company, China;1. College of Earth Sciences, Jilin University, 130061 Changchun, China;2. Key Laboratory of Oil Shale and Coexistent Energy Minerals of Jilin Province, 130061 Changchun, China;3. Key Laboratory for Evolution of Past Life and Environment in Northeast Asia (Jilin University), Ministry of Education, 130026 Changchun, China;4. China National Offshore Oil Corporation (Tianjin Branch), 300452 Tianjin, China;5. Daqing Oil Field Company, 163113 Daqing, China;1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China;4. SINOPEC Petroleum Exploration & Production Research Institute, Beijing 100083, China;1. Department of Earth and Environmental Sciences, University of Texas at Arlington, United States;2. School of Environment, Washington State University, United States;3. Department of Geology and Geophysics, University of Wyoming, United States;4. Department of Geosciences, University of Texas at Dallas, United States;5. Department of Geology and Geophysics, Louisiana State University, United States |
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| Abstract: | The Caddo Limestone forms economic carbonate reservoirs in Stephens County, northern Texas. This study demonstrates that, in the Caddo Limestone of the Eliasville and Breckenridge fields, porosity and permeability are best developed in phylloid-algal wackestones and packstones, as well as Komia wackestones and packstones prevalent within the uppermost interval (i.e., Cycle A) of the formation in the study area. The main reservoirs formed in the upper and middle intervals of the Caddo algal mounds because of meteoric dissolution related to subaerial exposure (which created a large volume of secondary pores) and early cementation that prevented mechanical compaction. A great portion of the secondary pores remain open, providing the principal pore spaces of the reservoir interval. Vugs (including moldic voids) are abundant, and dissolution-enhanced intragranular pores are very common within widespread Komia. Intercrystalline pores are prevalent in dolomitized and neomorphised lithofacies where micrite was converted to microsparitic and sparitic calcite. Micropores are abundant in the matrix and within grains (especially Komia fragments). The lower or basal interval of Cycle A is commonly much less porous owing to the substantial loss of primary pores by physical compaction and lack (or rare presence) of secondary pores. Laterally, wells in the areas with thicker Cycle A (interpreted as algal mounds) have higher porosity and thicker net reservoir than those in intermound areas. This work provides a case study of carbonate reservoirs in which Komia wackestones and packstones are the major reservoir rocks. |
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| Keywords: | Algal mound Carbonate lithofacies Diagenetic alteration Pore evolution Reservoir character |
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