Control of facies and fluid potential on hydrocarbon accumulation and prediction of favorable Silurian targets in the Tazhong Uplift, Tarim Basin, China

Abstract

Exploration practices show that the Silurian hydrocarbon accumulation in the Tazhong Uplift is extremely complicated. Our research indicates that the oil and gas accumulation is controlled by favorable facies and low fluid potential. At the macro level, hydrocarbon distribution in this uplift is controlled by structural zones and sedimentary systems. At the micro level, oil occurrences are dominated by lithofacies and petrophysical facies. The control of facies is embodied in high porosity and permeability controlling hydrocarbon accumulation. Besides, the macro oil and gas distribution in the uplift is also influenced by the relatively low fluid potential at local highs, where most successful wells are located. These wells are also closely related to the adjacent fractures. Therefore, the Silurian hydrocarbon accumulation mechanism in the Tazhong Uplift can be described as follows. Induced by structures, the deep and overpressured fluids migrated through faults into the sand bodies with relatively low potential and high porosity and permeability. The released overpressure expelled the oil and gas into the normal-pressured zones, and the hydrocarbon was preserved by the overlying caprock of poorly compacted Carboniferous and Permian mudstones. Such a mechanism reflects favorable facies and low potential controlling hydrocarbon accumulation. Based on the statistical analysis of the reservoirs and commercial wells in the uplift, a relationship between oil-bearing property in traps and the facies-potential index was established, and a prediction of two favorable targets was made.