TRANSFORMATION DYNAMIC FORCES AND HYDROCARBON ACCUMULATION OF THE YINGEN-EJINAQI BASIN

Three dynamic forces-ground stress, gravity and thermal dynamic force cause the transformation of basin and influence the hydrocarbon accumulation in the Yingen-Ejinaqi Basin. The transformation effect of ground stress is shown in 4 ways: uplift, extrusion, expansion and strike slip. Among which, the uplift postpones hydrocarbon accumulation in the denudation area, thus the thermal evolution of source rock remains the state before denudation, which is favorable for the preservation of palaeoaccumulation early generated and discharged. The extrusion effect results in fold, fracture and even tectonic reversal, offering not only various traps for hydrocarbon accumulation, but also force and passage for hydrocarbon migration. The expansion effect is shown by superposition of the Early Cretaceous rifts on the Jurassic ones. This transformation promotes the thermal evolution of Jurassic source rock, helping organic matters in source rock convert to hydrocarbon and migrate and accumulate. Meanwhile, extentional linked fractures partially change or destroy the original preservation condition of palaeoaccumulation, forming (secondary) hydrocarbon accumulation. The large-scale strike slip effect may form a series of transtensional and compresso-shear tectonic patterns, resulting in strike-slip pull-apart basin in the strike-slip expanding subsiding belt, and transforming preliminary basin. The influences on bydrocarbon accumulation include: a) providing environment and condition for accumulation; b) transformation and destruction. The gravity transformation effect is shown by deep burial and compaction, providing terrestrial heat field, geopressure field and preservation condition for hydrocarbon generation and accumulation. The quick occurrence of deep burial is also helpful for confining liquid pressure, resulting in abnormal overpressure, which is favorable for preserving primary pore, generating secondary pore and forming pressure seal, thus promoting hydrocarbon generation, migration and accumulation. The transformation effect of thermal dynamic force is shown by the transformation of sedimentary cover by multistage magma intrusion and effusion activity, providing favorable condition for hydrocarbon generation and accumulation.