Characteristics of the Upper Jurassic marine source rocks and prediction of favorable source rock kitchens in the Qiangtang Basin, Tibet

Abstract

This study evaluated the hydrocarbon-bearing potential of Upper Jurassic marine source rocks in the Qiangtang (羌塘) Basin through a comprehensive organic geochemical analysis of the samples from a large number of outcrops in different structural units to predict the location of favorable hydrocarbon kitchens, based on the evaluation standards of Mesozoic marine source rocks in the Qiangtang Basin. Rocks’ depositional environment, thickness and organic geochemistry feature were analyzed in this study. The principal controlling factors of the occurrences of favorable source rocks were analyzed. Upper Jurassic Suowa (索瓦) Formation source rocks are mainly platform limestone in the Dongcuo (洞错)-Hulu (葫芦) Lake deep sag and Tupocuo (吐坡错)-Baitan (白滩) Lake deep sag. Lithologically, the Suowa Fromation is made up of a suite of marls in intra-platform sags, micrites and black shales, which were all deposited in the closed, deep and static water depositional environment. Marl could form hydrocarbon-rich source rocks and its organic matter type is mainly II type in mature to highly-mature stage, the limestone forms a medium-level source rock. In addition, the favorable source kitchen of limestone is larger than that of mudstone. This study provides an important reference for the evaluation of Jurassic marine source rocks and for prediction of petroleum resources in the Qiangtang Basin.