Potential severity of phase trapping in petroleum reservoirs: An analytical approach to prediction

This study focuses on the evaluation and diagnosing of the potential severity of petroleum reservoirs for establishment of phase traps. In this area, very few diagnostic methodologies have been presented in the literature. Unfortunately, there is no universal agreement on the key influential factors in a phase-trapping phenomenon because each of the correlations was established on the basis of different sets of reservoir parameters (e.g., k; /; Swi; r) by use of the results of a number of aqueous-phase-trap tests over a limited range of rock and fluid properties. In the present work, an accurate technique is presented on the basis of the infiltration theory for prediction of the potential severity of phase-trapping damage. The fluid-saturation distribution around a well is analytically derived by linearizing and solving the governing partial-differential equation (PDE). Then, the calculated saturation profile in the vicinity of the wellbore is used to develop a new analytical diagnostic index, which is called a phase-trapping index (PTI). Knowing the fact that the saturation of the affected zone may be reduced to the irreducible rather than the initial value because of the capillary mechanics of the formation, interpretation guidelines are proposed to identify the regions that are susceptible to intense, serious, medium, and weak damage. Compared with other correlations, PTI offers several advantages such as generality, being founded on theory, and taking into account most of the key influential parameters. An example of a synthetic tight gas reservoir is presented to clearly demonstrate how the new technique can be applied.