Resource Potential Of The Huoshiling Formation In Dehui Fault Depression

The Huoshiling Formation in the fault depression in the eastern region contains a large area of gas-bearing strata and thus has a huge gas potential. Due to the complicated geology of this area, however, the gas hasn’t been explored intensively in general and there is not enough available chemical data about the hydrocarbon source rocks. So we lack a good understanding of the hydrocarbon potential of the Huoshiling Formation. In view of this problem, this study was conducted to assess the hydrocarbon source rocks in the formation qualitatively and quantitatively and was expected to provide a guidance for the exploration of gas in deep formations in the future.Dehui Fault Depression, located in the center of the uplifted zone in the southeastern Songliao Basin, was a NE depression composed of two faults. Previous research mainly focused on the analysis of two major source rock formations, the Yingcheng Formation and Shahezi Formation, but the Huoshiling Formation in Dehui Fault Depression has seldom been researched. According to the development, distribution and geochemical features of the hydrocarbon source rocks in this region, a qualitative assessment of the source rocks in the Huoshiling Formation was performed based on existing data. The borehole data indicated that mudstone widely occurred in this formation and dark mudstone was very developed. Coal was detected in the depression during drilling. Tests were conducted to measure the TOC, kerogen macerals, group composition of organic matter, carbon isotopic composition of kerogen, vitrinite reflectance, and other indicators of the source rock samples collected from this depression. Then using the measurements, a geochemical analysis and a qualitative assessment of the source rocks were performed in terms of the abundance, types, and maturity of organic matter. The threshold of hydrocarbon generation was obtained through this assessment. Last, a quantitative assessment of the source rocks was made by using the data on the region’s burial history, thermal history and hydrocarbon generation history and estimating the resource volume in this region. The results demonstrated that the source rocks in the Huoshiling Formation generally met the good or very good criteria. The organic matters were divided into three types, Ⅱ1, Ⅱ2, and Ⅲ organic matter, and were generally mature to highly mature, indicating that the Huoshiling Formation has a high hydrocarbon potential, especially the gas potential. For Dehui Fault Depression, the threshold of hydrocarbon generation was Ro=0.7%, the threshold of oil pyrolysis was Ro=1.1%, and the threshold of gas generation from coal was Ro=0.7%. The hydrocarbon generation in this formation occurred mainly in the 105Ma~80Ma period, approximately corresponding to the sedimentation period from the Quantou Formation to the Nenjiang Formation.The results of the resource volume assessment showed that the net oil reserves in the Huoshiling Formation reached 4678.2434 million tons and the total gas volume was 1186.792 billion m3. Setting the migration and accumulation coefficient at 2.06%, the gas volume in the Huoshiling Formation was estimated to be 24.448 billion m3.