Main factors controlling the formation of basement hydrocarbon reservoirs in the Qaidam Basin, western China

Basement hydrocarbon reservoirs are widely distributed worldwide. In recent years, a major breakthrough has been made in basement-rock hydrocarbon exploration in the Qaidam Basin, and basement-rock reservoirs have become important exploration targets in the basin. Basement hydrocarbon reservoirs are a special type of oil and gas reservoirs. This type of reservoir requires not only the same formation conditions as conventional hydrocarbon reservoirs but also some unique reservoir conditions. In this study, several geochemical, geophysical, and geological methods are used to assess the hydrocarbon accumulation conditions and mechanisms of the basement-rock reservoirs found in the Qaidam Basin, and the main factors controlling the reservoirs are proposed. Major hydrocarbon-generation depressions controlled the overall basement-rock reservoir distribution, paleo-uplifts (or paleo-salients) and paleo-slopes controlled the hydrocarbon migration directions, faults and unconformities controlled hydrocarbon-migration channel systems, and weathered-crust reservoirs of basement rocks controlled hydrocarbon enrichment. In addition, a suitable cap rock is an important requirement for preservation. Suggestions for future explorations have been put forward in this study, which will be of significance for guiding petroleum exploration in the area. Promising future exploration areas include the western part of the Kunbei fault-terrace zone in the front of the Kunlun Mountains, the paleo-uplift in the western part of the Altun Mountains front, and the Pingtai and the Mahai–Dahonggou paleo-uplift in the front of the Qilian Mountains.