Gas-generating potential of the Middle Permian saline lacustrine source rocks and significance for natural gas exploration in the eastern Junggar Basin
), Abstract
The Middle Permian saline lacustrine shales are identified as the most significant source rocks in the eastern Junggar Basin. Investigating their gas-generating potential and contribution to gas accumulation holds great significance for hydrocarbon exploration. Based on logs of wells newly drilled in recent years, as well as data from petrology, organic geochemistry, semi-open pyrolysis simulation experiments, and natural gas geochemical analysis, we systematically evaluate the gas-generating potential of the Middle Permian saline lacustrine source rocks, clarify the origin of natural gas from within, and delineate favorable targets for natural gas exploration. The results indicate that in the Dongdaohaizi Sag, the thickness of the Middle Permian saline lacustrine source rocks increases gradually from its margin to center, generally exceeding 350 m and reaching a maximum of 600 m at the center. In the Fukang Sag, two zones of thick Middle Permian saline lacustrine source rocks are determined, namely the northeastern margin and the south-central portion, where the source rock thicknesses primarily range from 200 to 250 m and exceed 400 m, respectively. The Middle Permian saline lacustrine source rocks in both sags principally exhibit medium to excellent quality, with oil-prone kerogen widely developed which is characterized by considerable thicknesses, high contents of retained hydrocarbons, and generally entering the gas window stage. All these suggest the potential for large-scale gas generation. The petroliferous gas generated by the Middle Permian saline lacustrine source rocks has been discovered in the eastern Junggar Basin, distributed primarily in the Fukang Sag, Dongdaohaizi Sag, and the Fukang fault zone. Besides, the petroliferous gas generated from the Middle Permian source rocks is also found mixed with the coal-derived gas in the Kelameili gas field and the Cainan oil and gas field. The ultra-deep reservoirs in the Fukang and Dongdaohaizi sags in the eastern Junggar Basin are favorable for the exploration of petroliferous gas, which can be divided into three favorable gas exploration zones: conventional gas outside source rocks, tight gas inside source rocks, and shale gas inside source rocks.
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References
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