四川盆地及周缘下寒武统页岩气成藏主控因素与勘探方向

Main factors controlling shale gas accumulation and exploration targets in the Lower Cambrian,Sichuan Basin and its periphery

运用最新的页岩气勘探理论及模拟实验结果,对四川盆地及周缘地区下寒武统页岩气成藏基本地质条件及主控因素进行了研究。该区下寒武统暗色泥页岩发育,可划分为"被动陆缘型"和"拉张槽型"2种类型。前者具有品质好、厚度巨大、分布范围广等特点,页岩气成藏物质基础条件优越,但底板条件差,构造变形强烈,页岩气保存条件受到挑战;后者达到了基本烃源岩标准,虽单层厚度薄,但具有纵向发育层段多、顶底板条件良好、构造变形弱等特点。高演化程度影响了暗色泥页岩的含气性,不利于页岩气富集成藏;顶底板条件是页岩气气藏早期形成的前提;构造条件是页岩气藏后期得以保存的关键。勘探有利区为盆内绵阳—乐至—隆昌—长宁地区及周缘城口—巫溪、鄂西宜恩—鹤峰、湘西花垣—张家界、贵州镇远等地区。

We studied the basic geological conditions and main controlling factors for shale gas accumulations in the Sichuan Basin and its periphery based on the latest theories for shale gas exploration and modeling results. Dark shale deposited in the Lower Cambrian can be defined as passive continental shale and tensional trough shale. The passive continental shale has good quality, great thickness and wide distribution. It has favorable basic conditions for shale accumulation, but the bottom plates are unfavorable and the structural deformation is exten-sive, thus the preservation conditions for shale gas are unfavorable. Tensional trough shale has reached the stand-ard of basic hydrocarbon rocks, though the thickness of single shale interval is limited. It developed many vertical layers with good top and bottom plates and weak structural deformation. High thermal evolution degree restricted the gas-bearing capacity of dark shale, which was unfavorable for shale gas enrichment. Top and bottom seals are necessary when shale gas reservoirs were formed during the early stage. Tectonic conditions are important for the preservation of shale gas during the late stage. The favorable area for shale gas exploration is Mianyang-Lezhi-Longchang-Changning in the Sichuan Basin, Chengkou-Wuxi in the northeastern Sichuan Basin, Yien-Hefeng in the western Hubei, Huayuan-Zhangjiajie in the western Hunan, and Zhenyuan in Guizhou.