Characteristics of Jurassic source rocks and oil and gas exploration direction in the piedmont zone between the south-western Qaidam Basin and Altun Mountain

The Jurassic petroleum system in the piedmont zone between Qaidam Basin and Altun Mountain is rich in oil and gas resources. Based on the sedimentary environment, geochemical analysis, and distribution prediction of the Middle-Lower Jurassic source rocks in the piedmont zone between the south-western Qaidam Basin and Altun tage region, the Jurassic oil and gas exploration potential in the area was systematically evaluated. The Jurassic source rocks in the study area are mainly coal, dark mudstone, and carbonaceous mudstone developed in the Lower Jurassic fan delta facies, as well as, oil shale, and mudstone in the Middle Jurassic of lacustrine facies, and coal measure strata of braided river delta facies. The thickness of Middle Jurassic source rocks is relatively thicker. Through restoration and weathered source rock samples analysis, the average TOC of the Middle Jurassic source rocks in the area can reach 4.19%, and the average chloroform bitumen "A" is 0.5915%, meeting the criteria for a good source stone. Every index is close to the Yuka Jurassic source rock, the highest quality found in the basin so far. At the same time, the distribution range of Jurassic source rocks in the study area is meticulously described through seismic facies identification and prediction analysis. Several Jurassic hydrocarbon generating centers in the area, such as Honggouzi - Yueyashan, Nanyishan - Xiaoliangshan, Pingxi, and Dafengshan, with thicknesses ranging from 200 to 400 m, indicating that the Jurassic source rocks have the material basis for large oil and gas fields formation.