Confirmation and distribution features of effective source rocks in Yinger Sag, Jiuquan Basin

Based on the basic theory of hydrocarbon generation and expulsion of source rock, TOC content, pyrolysis parameter S₁ and chloroform bitumen "A" content have been correlated to confirm the lowest limit of TOC content of effective source rocks from the Lower Cretaceous in the Yinger Sag. The lowest limit of TOC content of effective source rocks from the Xiagou Formation is 0.8%, while that from the Chijinbu Formation is 0.6%. Combining with the prediction from TOC content by single well logging, the thickness of effective source rock in single well has been calculated. The distribution of effective source rock in main layers has been confirmed combining the studies of sequence stratigraphy and sedimentology. Effective source rocks are well-developed in each layer, among which those in the Chijinbu Formation have the biggest thickness, and the Upper Xiagou Formation the second. In the Lower Xiagou Formation, effective source rocks are thin; however, they may increase to 250 m thick in the northern subsag, and 200 m thick in the southern subsag.