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Mechanism of Oil and Gas Accumulation of the Sinian, Central Sichuan Basin, China

Guosheng Xu, Jiaju Liang, and Xiao Wang
Chengdu University of Technology, Chengdu, Sichuan, China

The Sinian of the Sichuan Basin has experienced superposition transformations by Caledonian movement, Indosinian movement, Yanshan movement, Himalayan movement. Correspondingly, the associated oil and gas reservoirs have experienced multi-stage hydrocarbon-charging processes and complex phase changes. Using the geochemical methods and basin modeling, this study analyzed hydrocarbon accumulation mechanisms of the Sinian-Lower Paleozoic strata in central Sichuan Basin associated with multi-stage tectonic movements. Maturity evolution analysis of the Cambrian source rocks showed that the source rocks had obvious characteristics of secondary hydrocarbon generation. The primary hydrocarbon generation began in the Late Ordovician-Silurian, the oil generated in this period filled into reservoir of Sinian Dengying Formation, and the early paleo-oil pools formed. Uplift and erosion caused by the Caledonian movement resulted in the damage to the paleo-oil pools of Sinian Dengying Formation, leading to the formation of biodegradable asphalt. After the Permian, Cambrian source rocks remained deeply buried and generated a large number of hydrocarbons again in the late Triassic, thereby the paleo-oil pools of Sinian Dengying Formation formed once again. In the Middle-Late Jurassic, the Cambrian source rocks entered the stage of gas generation, and the crude oil in paleo-oil pools began to crack into gas, resulting in an abnormal overpressure. The oil-cracking gas and kerogen-cracking gas dissolved in formation water under abnormal overpressure conditions, leading to the formation of paleo dissolved-gas pools. Since the Late Cretaceous, substantial dissolved-gas exsolution occurred due to the uplift, leading to the gas readjustment and accumulation and the formation of modern Sinian gas reservoir. Therefore, for oil and gas reservoirs that have experienced multi-stage tectonic movements, an important mean to reduce the risk of oil and gas exploration is to analyze the hydrocarbon generation history of source rocks and evolutionary history of traps and preservation condition, as well as their coupling relationship.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013