Abstract:

Two sets of main hydrocarbon source rocks, Shahezi Formation and Yingcheng Formation, developed in the Lishu fault depression of Songliao basin, which had a favorable sedimentary environment, large thickness and wide distribution. The member Ⅱ of Shahezi Formation possessed the best conditions of forming shale gas, its TOC distribution range was 0.11%-8.20% (average value was 1.45%); Yingcheng Formation developed two members of   high quality mud shale: TOC distribution range of the member Ⅰ was 0.26%-12.01% (average value was 1.96%)，and that of the member Ⅱ was 0.06%-5.03% (average value was 1.06%). The main organic matter types were Ⅱ₁-Ⅲ, with few was type Ⅰ. The vitrinite reflectance (R_o) in Shahezi Formation was generally higher, whereas, in western fault depression it basically entered into over-mature phase, and it came into mature to high mature phase in gentle slope belt. In Yingcheng Formation, the range of variation of vitrinite reflectance (R_o) was large, and it reached over 2.00% in Xiaochengzi, Gujiazi and Shiwu. Mass fractions of brittle minerals of two sets of mud shale were 32.10%-62.90% which represents good reservoir properties. In the fault depression, there were several exploratory wells drilled with high gas logging show in the thick layers of mud shale in Shahezi Formation and Yingcheng Formation. The gas content was 0.62-3.09 m3/t in the member Ⅰ of Yingcheng Formation. With assessment by using the probability method, we preliminaryly forecast that Yingcheng Formation and Shahezi Formation possess shale gas resources amounting to 6 645.34 ×10⁸ m³. It is believed that Qinjiatun region and Sujiatun subsag are favorable target areas of shale gas exploration, and Sangshutai deep subsag belt is a relatively fine target area.

Key words: shale gas, resources potential evaluation, Cretaceous mud shale, Lishu fault depression, Songliao basin