黔中隆起及邻区下寒武统页岩气成藏特殊性分析

摘要

黔中隆起及邻区下寒武统牛蹄塘组页岩厚度大、有机碳含量高、热演化程度高、脆性矿物含量高,具备页岩气成藏的基本地质条件,但经过多年页岩气勘探实践,至今未取得实质性突破,主要受页岩气成藏条件的特殊性控制.在系统分析野外剖面以及黄页1井、龙页1井、丁山1井等资料的基础上,重点开展沉积相、页岩分布、有机碳含量、热演化程度等页岩基本地质特征和储集类型、储集物性及页岩含气性等页岩储层特征的研究,认为页岩气成藏条件特殊性主要表现在2个方面:(1)页岩热演化程度的特殊性,生烃、排烃历史复杂,热演化程度高,不利于页岩气的赋存和富集;(2)储层特殊性,热演化史复杂、成岩作用强导致页岩孔隙度较低,尤其有机孔发育少且孔径较小,页岩储集性差.在此基础上,制定了页岩气选区评价参数标准,评价了页岩气富集有利区.初步明确了黔南坳陷黄平地区具有构造相对稳定、页岩埋深适中、有机质热演化程度相对较低、保存条件较好及含气性好等特征,勘探风险程度相对较低,是黔中隆起及邻区页岩气勘探突破的Ⅰ类有利地区;黔西地区由于成熟度较高,是探索高热演化条件下页岩气藏的Ⅱ类有利区.%The Lower Cambrian Niutitang Formation shale is characterized by large thickness, high organic carbon content, high thermal evolution degree and high brittle mineral content in the Qianzhong uplift and its periphery. It has the basic geological conditions for shale gas accumulation. However, after many years of explo-ration, the study area has not made a substantial breakthrough, and some peculiar conditions for shale gas accu-mulation are the main controlling factors. Through the systematic analysis of outcrop sections and the data from wells including Huangye 1, Longye 1 and Dingshan 1, this paper focuses on the study of the basic geological characteristics of shale, including sedimentary facies, shale distribution, organic carbon content, thermal evolu-tion degree, and the shale reservoir characteristics, including reservoir types, reservoir physical properties and gas content. The peculiarities of shale gas accumulation conditions are mainly manifested in two aspects:(1) The particularity of high shale thermal evolution degree, with complex hydrocarbon generation and expulsion history, is not conducive to gas occurrence and enrichment. (2) The particularity of the shale reservoir. Complex thermal evolution and strong diagenesis resulted in low porosity, especially little organic matter pores and small diameter, which made the reservoir property of shale very poor. On this basis, some parameters for shale gas exploration were selected, and some favorable areas for shale gas enrichment were evaluated. The Huangping region in the Qiannan Depression is a typeⅠfavorable area of shale gas exploration in the Qianzhong uplift and its periphery, with relatively stable structure, moderate depth, relatively low thermal evolution degree of organic matter, favorable preservation conditions and good gas-bearing capacity. The exploration risk of the Huangping region is relatively low. Because of high maturity, the Qianxi region is a type Ⅱ favorable area to explore for shale gas reservoirs with high thermal evolution degree.