下扬子地区下寒武统荷塘组泥页岩地质特征与勘探前景--以浙西江山-桐庐地区为例

以往研究认为下扬子地区下寒武统暗色泥岩热演化程度普遍过高,制约了油气成藏,最新野外调查发现在浙西江山-桐庐地区存在热演化程度相对较低的区域。围绕该相对低值区域,以浙西区域地质调查资料、最新钻探的井下资料分析结果为基础,分析了江山-桐庐地区下寒武统荷塘组地质地化特征及页岩气勘探前景。该区荷塘组处于有利沉积相带内(深水盆地-陆棚相),具有沉积厚度大、有机质丰度高、热演化程度相对较低、脆性矿物含量高、黏土矿物含量适中、微孔隙微裂缝较发育等特点,认为该区具有较好的成藏物质基础。并以"高中找厚"(寻找高有机质丰度泥页岩沉积较厚区域)、"高中找低"(在普遍高热演化程度环境中寻找较低值区域)、"强中找稳"(在强构造背景中寻找地层稳定、埋藏较深区域)为原则,同时避开岩体以及岩浆活动较强烈的区域,优选出常山-开化地区为页岩气有利勘探区。

Geological characteristics and shale gas potential of Lower Cambrian Hetang Formation in Lower Yangtze region: a case study of Jiangshan-Tonglu area,western Zhejiang province

The high degree of thermal evolution is a main factor restricting the development of the Lower Paleozoic shale gas in the Yangtze region. The latest field study shows that there is a region with relatively lower thermal evolution in the Jiangshan-Tonglu area in western Zhejiang province. Centering on the lower thermal evolution area, this paper analyzes the geological and geochemical characteristics of the Lower Cambrian Hetang Formation, based on the regional geological survey of the western Zhejiang province and the latest borehole data analysis. The study area is located in a good sedimentary facies belt (basin-shelf facies), with a large deposition thickness, and a high organic matter abundance. While the thermal evolution degree is relatively low, with high brittle mineral content and moderate clay mineral content. And micro-pores and micro-fractures are well developed. The study area has a good material basis for accumulation. The Changshan-Kaihua area has been identified as the most favorable area for shale gas exploration on the basis of considering a thick shale deposit with high organic matter abundance, relatively low thermal evolution, stable tectonic background and deeply buried area, while avoiding the areas with relatively strong igneous activity.