Geological conditions and geochemical characteristics of favorable shale gas zones in Danzhai of the Qiannan depression
The Qiannan depression is located on the southwestern edge of the Yangtze block and is an important area of shale gas resources in South China. In recent years,significant progress has been made in shale gas exploration in this region. The shale in Cambrian Niutitang formation of the Qiannan depression is widely distributed,characterized by thick layers and abundant organic matter. Shale is developed in the mature stage and possesses significant potential for shale gas exploration and development. Although some progress has been made in the studies on shale in the Qiannan region,there is still a relative lack of in-depth research on the geological conditions,soluble organic matter,and reservoir formation mechanisms of the favorable zones. By measuring and collecting samples from typical profiles and survey wells of shale gas,this study systematically analyzed the geological conditions and organic geochemical characteristics of the favorable zones in Danzhai of the Qiannan depression. It also explored the distribution and development patterns of high-quality hydrocarbon source rocks in the Cambrian Niutitang formation.The results indicate that the Cambrian Niutitang formation in Danzhai is abundant in organic shale with a thickness of about 60 meters to 200 meters,showing an overall trend of gradually thickening from northwest to southeast. The total organic carbon content (TOC) of the Niutitang formation mainly ranges from 4.5％ to 6.0％,while the organic matter maturity (Ro) predominantly varies from 2.5％ to 2.7％,gradually decreasing from the northeast to the southwest. The mineral composition of shale in the Niutitang formation primarily consists of quartz,followed by clay minerals,and a small amount of carbonate minerals. The types of shale reservoir spaces include organic pores,inorganic pores,and microfractures,among which inorganic pores primarily consists of intergranular pores,intragranular pores,dissolution pores,etc. The shale matrix typically exhibits low porosity and permeability,categorizing the study area as a low porosity and low permeability shale reservoir. However,the development of local fractures can enhance both the porosity and permeability of shale. The tectonic activity has significantly influenced the preservation conditions of the strata and the degree of shale gas enrichment. Tectonic preservation continues to be a key factor affecting the shale gas enrichment of the Niutitang formation in Danzhai of the Qiannan depression. Due to relatively unfavorable enrichment conditions and the complex preservation of structures,the large-scale industrial development of shale gas in the Cambrian Niutitang formation faces significant challenges. However,the geological conditions of the shale in the Cambrian Niutitang formation in Danzhai are relatively favorable,indicating potential for further exploration of shale gas.
Qiannan depressionNiutitang formationblack shaleorganic geochemistryreservoir characteristicsfavorable zone of shale gas
万方数据
维普
