关键词: 简阳地区, 须家河组, 致密砂岩气, 构造样式, 控藏模式

Abstract: The tight sandstone gas resources are abundant in the Upper Triassic Xujiahe Formation in Sichuan Basin. However, the main accumulation-controlling factors of reservoir are not clear, and the gas production of single wells varies greatly, thus resulting in difficult in selection and assessment for hydrocarbon exploration area. Based on the core, imaging logging, seismic and single well test data, this paper determines the structural style, fracture characteristics, faults configuration and tectonic evolution history of the Member 4 of Xujiahe Formation in Jianyang area. On this basis, the main accumulation-controlling factors of gas reservoir are analyzed, and the structural accumulation-controlling model is put forward. The results show as follows. (1)There are two groups of NW- and NE-striking faults in Jianyang area. The NW-striking faults are developed in Xujiahe Formation, dominated by Grade Ⅳ faults, and the fault activity occurred during Indosinian to Early Yanshanian period. The NE-striking faults generally cut through Xujiahe Formation, dominated by Grade Ⅰ-Grade Ⅲ faults, and the fault activity occurred form Late Yanshan to Himalayan period. (2)The two groups of faults are associated with tectonic fractures that are consistent with the fault strike. The fractures are spatially crisscross and spread along the fault strike. (3)The tested gas production of single well in the Member 4 of Xujiahe Formation is closely related to fault development. The high-yield wells (with gas production greater than 20×10⁴m³/d)are all located in the NW-striking Grade Ⅳ fault zone, and its distance from the fault is less than 400 m. Moreover, the fractures are relatively developed in this area. Dry wells or water producing wells are generally distributed along the NE-striking Grade Ⅰ-Grade Ⅲ faults. Comprehensive analysis shows that the two tectonic events and their intensity have controlled the accumulation of natural gas in Jianyang area since the Late Triassic. The propagation of the Micangshan-Dabashan thrust belt into the basin during the Late Indosinian to Early Yanshanian period led to the development of the near EW- or NW-striking reverse fault zone with low deformation intensity in the basin (including Jianyang area), which combined with the associated fractures jointly contributed to the transformation of sandstone reservoirs in the Member 4 of Xujiahe Formation, and also the effective communication between the underlying source rocks in the Member 3 of Xujiahe Formation. This is conducive to the transport and filling of natural gas, thus achieving hydrocarbon enrichment and accumulation. During Late Yanshan to Himalayan period, under the influence of the SE-trending compression effect of the Longmenshan tectonic belt, tectonic deformation spread into the basin, developing NE-striking faults that break through the Xujiahe Formation. Such faults are prone to damage and adjust the early hydrocarbon accumulation system of the Member 4 of Xujiahe Formation, resulting in the loss of oil and gas along the faults. Based on these, this paper puts forward the structural accumulation-controlling model of "hydrocarbon accumulation controlled by source-reservoir adjacency and hydrocarbon enrichment controlled by NW-striking fault-fracture system" in Jianyang area, and points out that the NW-striking fault-fracture reservoir formed during the Late Indosinian to Early Yanshan period is a favorable exploration target.

Key words: Jianyang area, Xujiahe Formation, tight sandstone gas, structural style, accumulation-controlling model