川西南与川东北地区下志留统龙马溪组页岩气成藏条件对比及目标区分析

Comparison of Reservoir-Forming Conditions and Objective Exploration Zones of Shale Gas in Lower Silurian Longmaxi Formation of Southwest and Northeast Sichuan Basin

川西南与川东北是龙马溪组页岩气开发的有利勘探区域,对这2个区域龙马溪组页岩气的成藏条件进行了研究和对比,结果表明,川东北龙马溪组页岩比川西南具有更高的有机碳质量分数w(TOC)、热成熟度Ro和脆性度,但埋藏深度过大。利用层次分析法,对2个地区页岩气成藏条件做了定量对比,综合而言,川西南龙马溪组页岩成藏条件明显优于川东北。参照美国Fort Worth盆地Barnett页岩的选区原则,同时结合四川盆地自身的特点,选取页岩单层厚度、w(TOC)、Ro和埋藏深度4个评价参数,并对其标准经过适当修改后,确定了该套岩层的页岩气目标(核心)区与有利区。选区参数的信息叠合表明,龙马溪组页岩气目标(核心)区大致分布在川西南的自贡—内江一带以及宜宾以西;有利勘探区主要分布在川西南的马边—威远一线以东以及川东北的宣汉—万县一带。

Southwest and northeast Sichuan Basin are favorable exploration zones for the exploitation of Longmaxi Formation shale gas. The purpose of this paper is to study and compare reservoir-forming condi- tions of Longmaxi Formation shale gas between these two areas. It turned out that the shale with large depth in northeast is provided with higher organic carbon content, thermal maturity and brittle degree than in southwest. Reservoir-forming conditions of shale gas in the two areas are compared with the AHP quan- tificationally. Overall, the southwest Sichuan Basin is superior to the northeast on reservoir-forming con- ditions. Reference to the principles on the selection of favorable areas of Barnett shale in Fort Worth Basin and considering the characteristics of Sichuan Basin, this paper chose thickness distribution, organic car- bon content, vitrinite reflectance and burial depth to determine the objective and favorable zones of the res- ervoir. Superimposed parameter information indicated that the objective zones are roughly located around Zigong-Neijiang and west of Yibin areas in southwest; east of Mabian-Weiyuan in southwest and Xuanhan- Wanxian in northeast is the favorable zones for shale gas exploration.