A New Method for Computing Pseudoskin Factor for a Partially-Penetrating Well

Abstract

Abstract An accurate knowledge of pseudoskin is important to quantify an additional pressure loss due to partial penetration or restricted entry. Though several procedures for computing the pseudoskin factor have been reported in the literature, they are either insufficiently accurate for geometrically-complicated reservoir systems or require the solution of a fully-transient diffusivity equation. This study aims to present a new method for estimating the pseudoskin factor of a partially-completed well. It has been designed to overcome a limited applicability of previous methods in geometrical or computational aspects. The method is derived from applying the equation for the pseudosteady-state flow of a slightly compressible fluid and accommodates one or more openings in a single or multiplayer reservoir where a crossflow occurs between reservoir layers. The solution of a pseudosteady-state equation describes the pressure response of a closed radial system during a boundary-dominated flow period. A pressure drawdown of any reservoir system, which can be easily evaluated from the solution, is compared against the analytical solution of a fully-penetrated system. The pseudoskin factor is, then, determined from the difference between the two sets of results. Comparisons with previously published results are presented graphically. The reservoir types include various cases of homogeneous and multilayered systems with contrasting reservoir properties. It is shown that a highly accurate estimate of pseudoskin factor can be achieved regardless of the complexity of a reservoir system including the location of open intervals or number of layers. With minimum assumptions on the reservoir geometry, a greatly improved computational efficiency of pseudosteady-state approach permits the engineer to account easily for the effects of partial penetration on the productivity of a partially-penetrating well.