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

摘要： 四川盆地上三叠统须家河组致密砂岩气资源丰富,但成藏主控因素不明确,单井产气量差异大,给油气勘探评价选区造成了困难。综合岩心、成像测井、地震和单井测试等数据,厘定了简阳地区须家河组四段(须四段)的构造样式、裂缝特征、断层配置及构造演化历史,在此基础上剖析成藏的主控因素,提出构造控藏模式。研究结果表明:①简阳地区发育NW走向和NE走向两组断层。NW走向断层发育在须家河组内部,以四级断层为主,其活动时间在印支期—燕山早期;NE走向断层一般切穿须家河组,以一级—三级断层为主,其活动时间在燕山晚期—喜马拉雅期。②NW走向和NE走向两组断层均伴生与之走向一致的构造裂缝,裂缝在空间上沿断层走向呈交叉展布特征。③须四段的单井测试产气量与断层的发育密切相关。高产井(产气量＞20×10⁴m³/d)均位于NW走向的四级断层附近,且距断层的距离小于400 m,裂缝相对发育;干井或产水井一般分布在NE走向的一级—三级断层发育位置。综合分析认为,简阳地区晚三叠世以来发生的两期构造事件及其强度控制了天然气成藏。印支晚期—燕山早期,米仓山—大巴山冲断带向盆地内部扩展导致盆地内部(包括简阳地区)发育变形强度低的近EW走向或NW走向逆断层带,这类断层及其伴生裂缝共同改造了须四段砂岩储层,并有效沟通下伏的须家河组三段烃源岩,有利于天然气输导和充注,进而在须四段富集成藏。燕山晚期—喜马拉雅期,受龙门山构造带向SE方向的挤压作用影响,构造变形向盆地内传播,发育了NE向断穿须家河组的断层,这类断层易破坏并调整须四段早期的成藏系统,导致油气沿断层散失。简阳地区具有“源-储紧邻控藏、NW走向断-缝控富”的构造控藏模式,印支晚期—燕山早期形成的NW走向断-缝储集体为有利勘探目标。

关键词: 简阳地区, 须家河组, 致密砂岩气, 构造样式, 控藏模式