Sedimentary characteristics of the oil shales from the Dingqinghu Formation and evaluation of favourable oil shale exploration areas in the Lunpola Basin,Xizang

Abundant oil shales are exposed on a wide range of scales in the Lunpola Basin, Xizang. In the present paper, three oil shale distribution areas including Jiangriaco, Lunpori and Papa areas are evaluated on the basis of the study of oil shale sections, exploratory trenches, boreholes and relevant experimental data, as well as the thickness, quality, distribution and sedimentary facies of the oil shales in the Lunpola Bain, Xizang. On the whole, the oil shales in the Lunpola Basin have higher ash contents with an average of 81.76%, medium to higher oil contents with an average of 7.2%, ultra-low sulfur contents of less than 1% and higher total organic carbon contents with an average of 8.07%, and thus may be interpreted as the source rocks providing oil source for the reservoir rocks in the Lunpola Basin. The thickness of oil shales tends to be controlled by sedimentary facies. The oil shales are generally arranged along NW or SE orientation in the semi-deep lake and deep-lake sedimentary facies area of the Lunpola Basin. The average oil contents and total organic carbon contents of oil shales are relatively lower in the northwestern part and higher in the southeastern part of the Basin. Estimated from the thickness and extent of oil shales, the Papa area is believed to be the most favorable area for the oil shale exploration due to larger thickness, wider EW-oriented distribution, higher average oil contents and total organic carbon contents.