Dynamics mechanism and quantitative evaluation of effective reservoirs in petroliferous basins.

Effective reservoirs in petroliferous basins are generally defined as rocks that have relatively high porosity and permeability, which have the capacity for accumulating and storing hydrocarbons under the conditions of sufficient hydrocarbon supply. Previous studies show that the lower limit of porosity of effective reservoirs decreases with increasing burial depth. However, the existing assessment methods for effective reservoirs mainly use well test data or petrophysical properties of a reservoir, without considering the influence of depth. These methods are not practical for petroleum exploration. In this study, the dynamic mechanism of hydrocarbon accumulation was studied using physical simulation experiments, which revealed that capillary force is a basic control for hydrocarbon accumulation. The relationship between the capillary force ratio of surrounding rock to reservoir rock and their oiliness was statistically analyzed. Finally, a novel discriminating standard and quantitative evaluation for determining effective reservoirs was established and its reliability was confirmed. This study shows that the capillary force ratio of surrounding rock to reservoir rock determines the reservoir effectiveness. Moreover, a reservoir is more effective when the ratio is larger, thus more favorable for hydrocarbon accumulation. The reservoir potential index (RPI) ranging from 0 to 1 is introduced to characterize the hydrocarbon-bearing property of a reservoir. Rservoirs are classified as effective reservoirs when RPI <1 and ineffective reservoirs when RPI >1. The effective reservoirs are further divided into four grades based on the RPI value: Grade I: 0 ≤ RPI ≤0.25; Grade II: 0.25 < RPI ≤0.5; Grade III: 0.5 < RPI ≤0.75; Grade IV: 0.75 < RPI <1, in which the grade I refers to the most favorable reservoir. It is conformed as a practical and reliable method. • Dynamic mechanism of hydrocarbon accumulation is simulated. • Discriminating standard of effective reservoirs is established. • Capillary force difference inside and outside of rock is intrinsic for effectiveness. [ABSTRACT FROM AUTHOR]