Structure and reservoir-controlling of top Carboniferous weathering crust in Chepaizi area, Junggar Basin

Based on drilling data and integrated geological research, structural characteristics and main controlling factors of the weathering crust on top Carboniferous in Chepaizi area of the Junggar Basin were systematically analyzed. The development model of weathering crust structure and its reservoir-controlling was summarized. Results show that the weathering crust features in vertically layered structure, consisting of weathered clay layer, hydrolysis layer and weathering leached layer in top-down order. The weathered clay layer is thin and has limited areal distribution and poor physical property. The hydrolysis layer is thicker and has poor physical property but wide distribution in most areas. The weathering leached layer is very thick and has better physical property and extensive distribute in the whole area. The structure of the weathering crust is mainly controlled by facies of mother rocks, hiatus time and paleotopography. The weathered clay and hydrolysis layer serve as cap rocks for petroleum reservoir, while the weathering leached layer has favorable physical property and thus can serve as lateral migration pathway on top of the Carboniferous. Under the condition of the hydrolysis layer or weathered clay layer, double migration path model can be built which includes carpet sand and wea-thering crust. Otherwise, there would be one migration path with oil and gas channeling or irrigating. Under the control of weathering crust structure, there developed three types of reservoirs including weathered crust, carpet tip and composite lithology in the Carboniferous. © 2016, Editorial Office of Oil and Gas Geology. All right reserved.