METHOD OF DETERMINING THE NATURAL DRIVE INDICES AND OF FORECASTING THE PERFORMANCE OF THE FUTURE EXPLOITATION OF AN OIL POOL

摘要

The invention relates to a method of determining the drive indices and the original volume of hydrocarbons and of forecasting the future exploitation of an initially-undersaturated oil pool. The aforementioned indices are determined using the natural forces of gravity, viscosity and capillarity. In addition, the geological characteristics of the rock, expansion of the gas cap and the entry of water from the aquifer are also taken into account. The inventive method is based on the gradually-diminishing performance of the pressure in relation to the accumulated production of the pool or, more specifically, to the diminishing linear performance with marked variations in the slope of the pressure logarithm in relation to the accumulated production. Variations in the slope indicate variations in the natural drive mechanism of the pool. According to the invention, the variation in the accumulated oil production in relation to the pressure given by the first slope is used to estimate the original volume, while subsequent variations in the slope are used to deduce analytically parameters associated with the pool, such as productivity, drive indices, expansion and injection of fluids in the pool. When a variation occurs in the drive mechanism, the net effect of the drive of the rock/fluid system in a pool is the difference between the existing slope and the previous slope at said moment, the variations in the accumulated production in all of said parameters being implicit in the conditions of the pool.