Pressure Transient Behavior of Horizontal and Slant Wells Intersecting a High-Permeability Layer

Abstract

Abstract This paper describes numerical simulation studies designed to investigate the behavior of horizontal wells that intersect high permeability layers sandwiched between two lower permeability layers. The paper investigates the pressure transient behavior of 1) purely horizontal wells drilled in the middle layer and 2) slant horizontal wells that intersect all three layers, as the permeability of the high permeability layer is varied. A previous paper1 focused on late time interference effects and radial composite behavior caused by a limited high permeability layer. This study focuses on the early time dual permeability effect and its impact on recognition of conventional horizontal well diagnostic derivative slopes. The horizontal well simulations show a dual permeability effect as the contrast between the high permeability layer and the adjacent layers is increased. The vertical radial flow regime is seldom visible and masked by wellbore storage effects. Interestingly, what is observed however, is a plateau (or sometimes valley) caused by the dual permeability effect followed by a transition to horizontal radial flow regime. This may be explained as a combined effect of recharge and linear flow in the lower permeability layers. The plateau (or a valley) caused by the dual permeability effect, can easily be confused as representing the vertical radial regime. Similarly, the transitional data prior to horizontal radial flow, which includes the dual permeability effects, can be incorrectly analyzed and lead to misleading results. This paper will demonstrate the increased complexity of the pressure transient behavior when the well is slanted through all layers while intersecting the high permeability layer.