Heterogeneity Characteristics of Tight Reservoir and Gas Accaccumulation in Member 2 of Xujiahe Formation, Yingshan area, Northeast Sichuan
作者单位：Exploration and Development Research Institute of Daqing Oilfield Company Ltd
会议名称：《2020年中国地球科学联合学术年会》
会议日期：2020年
学科分类：081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程]
关 键 词：tightreservoir heterogeneity diagenesis XujiaheFormation Yingshanarea
摘 要：Tight gas reservoirs are widely developed in the Xujiahe Formation of the Sichuan Basin. Due to the strong heterogeneity of the reservoir, the gas-water relationship is complicated and the exploitation results are poor. The characteristics of the tight reservoir are systematically analysised in the Member2 of Xujiahe Formation of Yingshan area by thin sections and argon ion polishing scanning electron microscopy techniques. In combination with with X-ray diffraction, stable carbon and oxygen isotope, trace elements, the formation mechanism of heterogeneity of tight reservoir is analyzed and the matching relationship between gas accumulation and development of tight reservoir is discussed. The results show that the reservoirs of Member2 of Xujiahe Formation in Yingshan area are mainly composed of feldspar quartz sandstone, lithic feldspar sandstone, and feldspar lithic sandstone. The types of storage space are mainly intergranular pores and intragranular dissolved pores, with an average porosity of 9.47% and an average permeability of 0.14×10-3μm. They are low-porosity and low-permeability reservoirs. The study area experienced relatively strong mechanical compaction, which severely damaged the primary porosity of the reservoir, with an average decrease of 15.27%, which is the main reason for the overall densification of the Member2 of Xujiahe Formation. However, the change of the vertical physical properties of the Member2 of Xujiahe Formation is closely related to the calcite metasomatism and cementation. The tight layer usually appears in the middle of the thick sandstone, with a thickness of 2 to 4 m and a certain distribution range in the transverse direction. The cement and metabolites of calcite mainly form the Middle and Late Cretaceous. At this time, the formation temperature is 120～140℃, and the source rocks are at the peak period of hydrocarbon generation. Thus the high carbonate mineral composition in the source rock of Yingshan area, the organic acid-rich fluid discharged can carry more Ca2+ and HCO3-ions into sandstones rich in feldspar and other alkaline minerals. An environment conducive to the precipitation of calcite cements and metabolites was formed, resulting in the formation of a tight interlayer of calcite. The large-scale Middle-Late Cretaceous oil and gas filling, which was blocked by the tight layer, made the gas reservoir a of sweet spots area in a reservoir with excellent pore conditions.