The Practical Aspects of Interlayer Crossflow

Abstract

As a result of knowledge gained from recent theoretical work, the production and/or pressure response of wells in layered oil or gas reservoirs can be interpreted to determine whether communication exists between the layers. If cross-flow between layers can occur, the pressure and production behavior of a well can be represented or interpreted by use of homogeneous reservoir theory. A well in a layered reservoir with crossflow behaves as a well in a homogeneous, single-layer reservoir which possesses the same dimensions and pore volume as the crossflow system and a "kh" product (permeability-thickness product) equal to the total "kh" of the crossflow system. The occurrence of crossflow can be confirmed by the "homogeneous-like" appearance of the pressure and/or production decline data and by the absence of "layer effects" which appear when crossflow does not occur. These layer effects in reservoirs without crossffow are characterized by sharply rising sections on the late-time portion of pressure build-up curves and by continuously changing production decline rates. Interlayer crossflow in oil or gas reservoirs can have a significant effect on exploitation economics. If crossflow can occur, the result is a shorter operating life and a higher primary ultimate recovery. Crossflow may obviate the need for perforating and treating long sections of low-permeabil-ity rock.