| Both the tectonic setting and the distinctive tectono-sedimentary features of Songliao basin, a significant oil-bearing basin in China, gave rise to the rich resources of oil and natural gas in the basin. The latter has been confirmed to be of a great value in exploration. For the purpose of development and utilization of oil and natural gas in Songliao basin, it is urgently necessary to make a detailed study of the formation of natural gas pools therein, and then to conduct a quantitative appraisal of exploration targets for deep natural gas.In this study, a variety of aspects were addressed, including tectonic evolution of the basin, geological conditions for forming natural gas pools, simulation of gas pool formation process, recognition of natural gas pools, appraisal of exploration targets for natural gas at depth, and possibility of pooling natural gas derived from the mantle. Major conclusions drawn from these researches are listed as follows.There existed good geological conditions for the formation of natural gas in Songliao basin, such as favorable geological setting, several suites of source rocks rich in hydrocarbon, several reservoir layers that mostly consist of sandstone, spatial imposition of sources, reservoirs, and capped rocks, migration, and preservation. This implies the possibility of having the large-scale gas field in the basin.As indicated by the modeled burial history and the modeled thermal history of Songliao basin, the geo-temperature rose swiftly as a response to fast sedimentation of Jurassic rocks to the lower part of the first member of Qingshan formation, and reached maximal in the end of Mingshui formation. The maximal geo-temperature was 102 °C at the bottom of the first member of Qingshan formation, and 307 °C at the bottom of Jurassic rocks, comparing with 94 °C and 291 °C now at the two levels, respectively, owing to the small thickness of Tertiary and Quarternary sediments.According to the study of hydrocarbons generation at depth, Jurassic rocks entered into the stage of gas generation in the end of Jurassic period. The accumulative amount of natural gas generated from the end of Jurassic period to the end of Quantou formation was estimated to be 24.31×1012 m3, or about 45% of the total gas generated, with a speed of 0.972×1012 m3/Ma. This was the first and the most important peak of gas generation in the basin. The second peak was in the time of middle Runjiang formation when both Denglouku formation and the first and secondmembers of Quantou formation entered in gas generation in a vast amount.For Jurassic source rocks, hydrocarbon expulsion threshold is 2000 m, and the peak of expulsion is during the sedimentation of the first member of Qingshan formation to Neocene rocks, with a palaeodepth of 2900 45 00m. At the time, the amount of hydrocarbon expulsion is 11.5m3 per square of source rocks, the efficiency of which is 83.3%. Till now, the accumulative amount of gas diffusion is 17.10X 1012m3, the amount of gas dissolution is 2.09X1012m3, and the amount of gas dissolution and absorption 7.36X1012m3. In this sense, when the first and second members of Quantou formation played an role of capped rocks, the amount of residual natural gas was 5.92 X 1012m3, of which the amount of gas resources in rocks below Quantou formation was 1800X108m3. In the end of sedimentation of Qingshan formation, the accumulative amount of deep natural gas was 48.74 X 1012m3 , indicating that only the gas generated late, 5.16X 1012m3 in amount, might have been capped. The amount of natural gas in rocks above the first and second members of Quantou formation was 1500X 108m3. So, there are about 3300 X 108m3 of natural gas in the basin.In this study were established physical parameters change regularity (i.e. seismic velocity, wave impedance, poisson's ratio in rocks, etc.) of rocks under differing geological conditions (i.e. at variable depth in the east and in the west of the basin, respectively). In order for recognizing deep natural gas in the basin, techniques of high-resolution collection, high-resolution process, and seismic discrimination of gas pools were promoted, which resulted in the discovery of Laozhou gas pool and Aonan-Heidimiao gas-bearing area.As confirmed by this study, natural gas accumulated at the overlap, consisting of Jurassic rocks and the second and fourth members of Denglouku formation, above the Anda-Zhaozhou anticline. It also accumulated in the third and fouth members of Denglouku formation, and in the overlap of Jurassic rocks and the first member of Dnglouku formation, to the north of Xujiaweizi. The author suggests that these two areas are of great value in exploration of deep natural gas in the basin.In Songliao basin there is also abundant inorganic natural gas is derived from the mantle. It is distributed along the large fracture zones and their subsidiary faults, as well as unconformities in the basin, inorganic gas is believed to accumulate primarily in the decollement in the deep crust that is characterized by low seismic velocity, low density and high conductivity, and then to migrate upwards into the basin along the large fracture zones. A new exploration of natural gas in Songliao basin is hence to look for industrial mantle-derive natural gas pools.
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