Sinian hydrocarbon accumulation conditions and exploration potential at the northwest margin of the Yangtze region, China

Based on outcrop, drilling, logging and seismic data, the reservoir forming conditions, reservoir forming model and exploration potential of the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze craton region were examined. (1) This area is in craton rifting stage from Sinian to Early Cambrian, characterized by syn-sedimentary faults and rapid subsidence, significant sedimentary differences, and development of Dengying Formation platform margins on both sides of the rift. (2) The Sinian-Cambrian in this area has two sets of high-quality source rocks, Doushantuo Formation and Maidiping-Qiongzhusi Formation; of which, the latter has a thickness of 150-600 m and hydrocarbon generation intensity of (100-200)x108 m3/km2. (3) The mounds and shoals in the platform margin of Sinian Dengying Formation controlled by faults are thick and distributed in rows and zones; they are reformed by contemporaneous-quasi-contemporaneous and supergene karstification jointly, forming pore-type reservoirs with a thickness of 200-400 m. (4) The two sets of source rocks enter oil generation windows from Permian to Early Triassic, and the oil migrates a short distance to the lithologic traps of mounds and shoals to form a huge scale paleo-oil reservoir group; from Late Triassic to Jurassic, the oil in the paleo-oil reservoirs is cracked into gas, laying the foundation of present natural gas reservoirs. (5) The mound-shoal body at the platform margin of Dengying Formation and the two sets of high-quality source rocks combine into several types of favorable source-reservoir combinations, which, with the advantage of near-source and high-efficiency reservoir formation, and can form large lithologic gas reservoirs. The Mianyang-Jiange area is a potential large gas field with trillion cubic meters of reserves. According to seismic prediction, the Laoguanmiao structure in this area has the Deng-2 Member mound-shoal reservoir of about 1300 km2, making it a ultra-deep target worthy of exploration in the near future.

Automated summary

Based on geological data analysis, the ultra-deep Sinian Dengying Formation at the northwest margin of Yangtze craton region has significant exploration potential and huge lithologic gas reservoirs. This area was in the craton rifting stage from the Sinian to Early Cambrian, characterized by syn-sedimentary faults and rapid subsidence, as well as the formation of Dengying Formation platform margins. There are two sets of high-quality source rocks in the Sinian-Cambrian, and the mounds and shoals controlled by faults in the Dengying Formation platform margin have thick pore-type reservoirs. The mound-shoal body and source rocks form favorable source-reservoir combinations that can create large lithologic gas reservoirs.