汉中地区构造演化及寒武系页岩气形成地质条件研究

近年来陕南地区页岩气勘探取得了一定的成果,与其同属扬子板块北缘的汉中地区也被认为具有较好的页岩气资源前景。本文利用野外地质调查、二维地震、岩石学及有机地球化学等资料,对汉中地区构造演化及寒武系页岩气地质条件开展研究。结果表明,汉中地区经历了南华纪—三叠纪海相演化、三叠纪末—白垩纪陆内演化和新生代断陷盆地三个演化阶段,寒武系牛蹄塘组和石牌组为海陆过渡相沉积,其中暗色泥岩有机质类型以Ⅱ1型和Ⅱ2型为主,TOC含量0. 45%~2. 79%,Ro为0. 61%~1. 21%,整体属于中等—好的成熟烃源岩,具备良好的生烃潜力;且牛蹄塘组灰黑色粉砂质泥岩中有机质较为丰富,石英等脆性矿物及黏土矿物含量较高,微裂缝及孔隙发育,有利于页岩气生成、赋存以及后期开发。综合分析认为汉中地区寒武系具备良好的页岩气资源前景,且东部地质条件优于西部。

Tectonic evolution and geological conditions for the formation ofCambrian shale gas in Hanzhong area

In recent years, significant progress has been made in shale gas exploration in southern Shaanxi. The Hanzhong area, located along the northern margin of the Yangtze Plate, is also considered to have promising shale gas resource potential. This study focuses on investigating the geological conditions and evolutionary history of Cambrian shale gas in the Hanzhong area using field geological surveys, 2D seismic analysis, petrological examinations, and organic geochemical data. The results show that the Hanzhong area has undergone three stages of geological evolution: marine evolution from the Nanhua to the Triassic period, intracontinental evolution from the end of the Triassic to the Cretaceous period, and Cenozoic rift basin formation. The Cambrian Niutitang Formation and Shipai Formation represent transitional facies deposits, characterized by dark mudstone containing predominantly type Ⅱ1 and Ⅱ2 organic matter. These shale formations exhibit a total organic carbon (TOC) content ranging from 0. 45% to 2. 79%, with a maturity level (Ro) between 0. 61% and 1. 21%. These characteristics classify them as medium- to good- mature source rocks, indicating significant hydrocarbon generation potential. In addition, the gray- black silty mudstone of the Niutitang Formation is rich in organic matter and contains high contents of brittle minerals such as quartz and clay minerals. This formation also exhibits well- developed micro- fractures and pores, which are favorable conditions for the generation, occurrence, and subsequent development of shale gas. The study concludes that the Cambrian system in the Hanzhong area holds promising shale gas resources, with the geological conditions being more favorable in the eastern part compared to the western part.