Shawan Formation pool-forming system and enrichment regular pattern in Chepaizi uplift, western Junggar Basin, China.

The hydrocarbon reservoirs in Chepaizi uplift in the western Junggar Basin were far away from oil source. Neogene reservoirs and hydrocarbon are mostly within thick sandstone and the overlying thin sandstone. It has intimate communication of hydrocarbon sources between the oil of thick sandstone and the oil of overlying thin sandstone. In view of this appearance, the authors research the reservoir-forming system, by area structure, geochemical correlation between oil and source rock, migration system, laboratory test, pool-forming feature. It made the conclusion that the lightweight oil source rocks were Jurassic strata, which were mainly migrated from the western Changji sag with direction from southeast to northwest. The Jurassic/Cretaceous unconformity and the long-term flexible Hongche fault constituted oil migration passage, and the oil from the deep Changji sag could migrate long distance to shallow uplift. The highly horizontal conduction efficiency by the thick sand distributed widely in the First Member of Shawan Formation was the key point of the oil and gas's scale enrichment in Chepaizi uplift. The vertical connection of the minor Himalayan fault facilitated pool-forming in sand lithostrome in the Second Member of Shawan Formation. The Jurassic/Cretaceous unconformity, the Hongche fault and the thick sandstone in the First Member of Shawan Formation contacted closely and matched well, they constituted the composite and dynamical conduction framework. The authors researched the pool-forming system, generalized the pool-forming pattern, and proposed that the lithologic hydrocarbon reservoir in the the Second Member of Shawan Formation and the updip pinchout or the overlapped hydrocarbon reservoir in the First Member of Shawan Formation were the optimum exploration target.