The natural-gas hydrate exploration prospects of the Nayixiong Formation in the Kaixinling-Wuli Permafrost, Qinghai-Tibet Plateau

摘要

Critical components of the Qinghai-Tibet Plateau natural-gas hydrate (NGH) petroleum system has been examined in this study. The results demonstrate that the Kaixinling-Wuli permafrost region contains viable prospects for gas hydrate exploration within favorable temperature and pressure stability conditions. In the study area, the average annual temperature of ground surface is -4.2 degrees C, the thickness of permafrost ranges from 40 to 150 m (average 84 m), and the geothermal gradient beneath the permafrost is between 1.54 degrees C/100 m and 2.67 degrees C/100 m (average 2.03 degrees C/100 m). The thickness of the methane gas hydrate stability zone (GHSZ) is approximately 240-450 m. The Upper Permian Nayixiong Formation is dominated by braided delta and shallow shelf facies under mostly reducing conditions. The potential swamp deposited source rocks have a high total organic carbon (TOC) content that features a mixture of kerogen types II or III and an average vitrinite reflectance (R-o) of 2.04%. Overall, the thick sedimentary column in this region, its abundance of organic matter and its high thermal maturity suggest that the Nayixiong Formation source rocks have a high gas-generation potential. An effective fault-fracture-pore system also provides migration channels for deeper gas and also act as a reservoir for vein-type gas hydrate occurrences. The Kaixinling-Wuli area, when compared to other regions in the Qinghai-Tibet Plateau, exhibits greater gas hydrate petroleum system exploration potential as a result of the favorable temperature/pressure stability conditions and effective gas and gas-hydrate migration-storage system. (C) 2016 Elsevier Ltd. All rights reserved.