Pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs: a case study of the Mesoproterozoic Changcheng System in Ordos Basin
LIU Hengyu1,2, LIU Mingjie1,2, HAO Zhilei3, REN Yin4, WU Enyu1,2, XU Han1,2, ZHONG Shoukang1,2, TAN Xiucheng1,2, ZENG Wei1,2, LIAN Chengbo1,2, DAI Hongming1,2
1 Sichuan Natural Gas Geology Key Laboratory,Southwest Petroleum University,Chengdu 610500,China; 2 School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China; 3 Exploration Department,PetroChina Changqing Oilfield Company,Xi'an 710018,China; 4 Geology Research Institute,Greatwall Drilling of CNPC,Liaoning Panjin 124010,China
Abstract：To investigate the pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs,a combination of core,thin section,scanning electron microscopy,X-ray diffraction and fluid inclusion analysis techniques was used to systematically analyze the sedimentary environment,petrology,reservoir space,porosity and diagenesis of the deep sandstone reservoirs of the Changcheng System in the central and eastern Ordos Basin. On this basis,the mechanisms of pore formation and preservation was clarified. The results show that the Changcheng System mainly develops quartz sandstone and lithic quartz sandstone in tidal channel sedimentary environment,with medium textural maturity and high compositional maturity. The reservoir space is dominated by residual intergranular pores and intragranular dissolution pores of rock fragments,with an average porosity of 6.6%. The compaction of the Changcheng System sandstone is generally strong,and it is mainly composed of quartz and illite cementation. The acidic dissolution of rock fragment is the most developed,followed by alkaline dissolution of quartz. The results indicate that the coarse grain size,good sorting and low matrix content are the main reasons for the primary pore development in the Changcheng System tidal channel sandstones,which formed under strong hydrodynamic conditions. The Changcheng System sandstone reservoirs have experienced leaching dissolution of meteoric fresh water during the early stage,organic acids dissolution during the middle stage and alkaline dissolution of quartz during the late stage,which provides favorable conditions to the formation of secondary pores. The pore preservation of the Changcheng System sandstone reservoirs is mainly attributed to the rich in rigid compressive quartz grains,coarse grain size and good sorting,the quartz cementation inhibited by early authigenic clay coating and the burial process of early long-term shallow burial and rapid deep burial in the later stage.
LIU Hengyu,LIU Mingjie,HAO Zhilei et al. Pore formation and preservation mechanisms of ancient deep tight sandstone reservoirs: a case study of the Mesoproterozoic Changcheng System in Ordos Basin[J]. JOPC, 2024, 26(6): 1435-1451.
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