Analysis of the shale gas formation conditions in the Lower Cambrian Niushutang Formation at the periphery of the Zhongbao Fracture in Zhenping County, Shaanxi, China

The organic-rich shale layer system present in the Lower Paleozoic period was more prevalent in southern Shaanxi,which is a prime location for shale gas exploration.The black shale of the Lower Cambrian Niutitang Formation at the Zhongbao Fracture periphery in Zhenping County has a substantial thickness and even distribution,and is dominated by type I kerogen.The distribution of organic carbon ranged from 1.27% to 11.72%,with an average of 3.42%,indicating a high abundance of organic matter.The reflectance of vitrinite in the shale ranges from 2.48-3.48%,with an average of 3.18%,which is in the over-mature stage with good potential for hydrocarbon production.Shale reservoirs possess ample storage space and a high content of brittle minerals,which are favorable for fracturing and reservoir transformation.The ZBDR01 well showed good oil and gas display,successful drainage test ignition,and a flame height of 2-3 m.Gas source analysis indicates that it is a marine oil-type cracked gas with high maturity.Preliminary geological studies suggest that it is the hydrocarbon source rock of the Niutitang Formation,indicating that the Ankang area of Shaanxi has favorable shale gas formation conditions.The 2D seismic data interpretation results show that the preliminary area of the favorable zone in the Lower Cambrian Niutitang Formation was approximately 102 square kilometers.