Characteristics of Hydrocarbon Source Rocks in Lower Permian Maihanhada Formation in Hangwula Region of Alashan Right Banner

Based on the study of lithologic characteristics and oil and gas geochemical features of dark mud shale in the Lower Permian Maihanhada Formation in Hangwula region of Alashan Right Banner,the vertical distribution,organic matter abundance,kerogen type and thermal evolution of the source rocks are summarized here.The total thickness of the enriched dark mud shale is 160.1 m which contributes 33.3% of the clastic rocks.The thickness of the dark mud shale controlled by samples is 94.1 m.The average organic carbon content is 0.75%,and 93.5% samples are more than 0.3%.Among the samples controlled dark mud shale,the better source rocks with organic carbon content over 1.0% are 23.6% with total thickness of 22.2 m,the middle source rocks with organic carbon content between 0.5%~1.0% are 48.3% with total thickness of 45.5 m,the worse source rocks with organic carbon content between 0.3%~0.5% are 17.5% with total thickness of 16.5 m.The sterane relative content is obvious advantage of C27 and the content of saturated hydrocarbons of group composition is obviously higher than aromatics.The kerogen is type II.The average general vitrinite reflectance is 0.77% which indicates that the kerogen underwent mature stage.The maximum pyrolytic temperature(Tmax) is from 350 to 550 ℃,which shows the source rocks belong to mature or high mature stage.It is concluded according to comprehensive evaluation that the source rocks in the lower Permian Maihanhada Formation have better hydrocarbon genesis potential,and mainly produce gas.