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The Relationship Between Tempo-pressure Evolution and Accumulation Process of Deep Carbonate Reservoir in the Central Paleo-uplift, Sichuan Basin, Southwest China


The exploration of deep-buried reservoir is the new realm of world hydrocarbon resources. The central paleo-uplift of Sichuan Basin is a favorable place for gas accumulation. In the Mo-Gao block of the uplift, a gas field in the deep carbonate with 10×1011m3 has been discovered in the Cambrian Longwangmiao Formation (∈1l) and Sinian Dengying Formation (Z2d). The burial depth is more than 5000m. The paper discussed the evolution of temperature and pressure in Mo-Gao block, and the control action to diagenesis and accumulation. The evolution of temperature and pressure were recovered by the methods of inclusions PVT and basin modelling. Inclusion tests showed that the homogenization temperature of ∈1l mostly distributed in343-353K, 573-593K with the trap pressure coefficient 1.4-1.7. In Z2d, the homogenization temperature mostly distributed in 353-363K, 573-593K with the trap pressure coefficient 1.2-1.4. Comprehensive analysis revealed that the evolution of reservoir could be divided into three stages. At the end of Permian, the paleo-uplift began to subside rapidly. The temperature, pore pressure and source rock maturity increased quickly. Before the large oil cracking at the late Triassic, the temperature reached 333K and the pressure was normal. The early reconstruction of reservoirs was completed. It's worth noting that there was a period of hydrothermal minerals in ∈1l destroyed the reservoir space which had a great influence on the overpressure. From the late Triassic to the mid Cretaceous, the temperature increased from 333K to 573K, the large scale of oil cracking happened both in source rocks and reservoirs. At this period, the overpressure began to form and reached the maximum. However, the pressure coefficient of ∈1l was bigger than Z2d. Due to the cracking occurred earlier in Z2d, a certain of potential difference would appear leading to the gas generated late spread into ∈1l forming stronger overpressure. From the late Cretaceous to the present, the Mo-Gao block suffered rapid uplift with the temperature and pressure reduced quickly. At the end of Sinian, the Z2d suffered from weathering leaching process for a long time. The thick vadose zone and leached zone developed at the top of carbonate rocks with early fissures distributed widely. It was the late uplifting that made the fissure further developed, which decreased the pore pressure more. As a result, the current pressure coefficient of Z2d is 1.01-1.12, but 1.56-165 in the ∈1l reservoir.