Typical filling models of a fractured-vuggy system in carbonate rocks under a moist environment

Carbonate reservoirs have strong heterogeneity, and were filled during multiple periods of karstification, which makes hydrocarbon exploration difficult. The Ordovician palaeo karsts in the northern Tarim Basin and the modern karsts in Guilin are examples of karst development in a moist environment, which have similar conditions and characteristics of karst development.According to the principles of "from the surface to the center" and uniformitaranism, combined with oil characteristics and previous research results, we established several typical filling modes of the fractured-vuggy system in carbonate rocks under a moist environment. According to hydrodynamic conditions and filling materials, they can be divided into exogenous underground river filling and endogenous filling models.According to filling structure classification, they can be divided into upper and lower structure filling model, circle structure filling model, and embedded mixed filling model.These models have various filling degree and types of filling material, and the corresponding karst reservoirs also have different physical properties.Generally speaking,the reservoir performance of the exogenous underground river filling modelis better than that of the endogenous filling model, and the reservoir performance of the upper and lower structure filling model is better than that of the circle structure filling model.