The Relationship between Karst Palaeogeomorphology Recovery and Gas Enrichment in Ordos Basin:Example from Mawu Section of Ordovician Majiagou Formation in Gaoqiao Area

Taking the Mawu section of Ordovician Majiagou Formation in SA79 oil well region of Gaoqiao area, Ordos Basin as an example, after analyzing the drilling, comprehensively cores, well logging, seismic and analysis assay data, the karst palaeogeomorphology has been recovered by the traditional geological analytic method, impression method and residual thickness method, the controlling action of Ordovician karst palaeogeomorphology on gas distribution in Ordos Basin has analyzed, and the favorable exploration region has been predicted.The results show that the SA79 oil well region is located in the slope position of karst palaeogeomorphology, with the morphology of west high and east low; The karst monadnock was partially developed, and the karst depression was occurred in the eastern part.The karst palaeogeomorphology is obviously controlled the enrichment of gas, and the gas was mainly enriched in the slope position at the front end of depression and monadnock between monadnock belt and depression.