Breakthrough in the exploration of bauxite gas reservoir in Longdong area of the Ordos Basin and its petroleum geological implications

Recently, high-yield industrial gas flow is produced at a rate of 67.38×104 m3/d by Well L47 which is deployed by PetroChina Changqing Oilfield Company in the Paleozoic in Longdong exploration area of the southwestern Ordos Basin, marking a great breakthrough in the exploration of bauxite gas reservoirs in this area. In order to further clarify the exploration and development potential of bauxite gas reservoirs, this paper systematically analyzes the reservoir characteristics, source rocks and traps based on the data of bauxite cores, field outcrops, mud logging, wireline logging and assay. In addition, the factors controlling the formation of bauxite gas reservoirs are explored, and the exploration potential of Paleozoic bauxite gas reservoirs in the southwestern Ordos Basin is evaluated. And the following research results are obtained. First, the breakthrough in the exploration of this bauxite gas reservoir in the Ordos Basin benefits from the change of the intra-source unconventional exploration idea, which starts a new field of gas exploration in the Ordos Basin. Second, this bauxite reservoir is controlled by sedimentary paleoenvironment and paleogeomorphology and its reservoir space is dominated by dissolution pores. Thick layers of bauxite diagenetic mineral are deposited in the environment of lagoon. There are favorable conditions for the development of high-quality bauxite reservoirs in the low position of paleogeomorphology. Third, the Upper Paleozoic coal-measure source rocks are the main gas source rocks, which are in direct or indirect contact with the Paleozoic bauxite reservoir, so a good source-reservoir configuration relationship is formed. Fourth, the main trap type of gas reservoir is lithologic trap. In the background of tectonic uplift in the eastern Ordos Basin in the Yanshanian period, there is an effective barrier of lithofacies change in the updip direction of the bauxite reservoir. In conclusion, the breakthrough in the exploration of bauxite reservoir not only makes Changqing Oilfield more confident in natural gas reserve and production increase, but it is also of important implications for the exploration of bauxite gas reservoirs in other areas of North China. © 2021, Natural Gas Industry Journal Agency. All right reserved.