The Effect of Skins at a Natural Fracture Crossed Normally by a Finite Horizontal Well
- Michael Prats (Michael Prats & Associates Inc.) | Rajagopal Raghavan (Phillips Petroleum Co. (Retired))
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- January 2013
- Document Type
- Journal Paper
- 233 - 242
- 2013. Society of Petroleum Engineers
- 5.8.6 Naturally Fractured Reservoir, 5.6.4 Drillstem/Well Testing
- 1 in the last 30 days
- 425 since 2007
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The effect of zones of impaired permeability at the faces of natural fractures on the performance of a finite-length well, completed normal to the fracture in an infinite 3D system, is analyzed by use of known analytical procedures capable of considering large ratios of fracture permeability to matrix. The zones of impaired permeability, called fracture skins, are represented as planes of equivalent flow resistance. The most important findings of this scoping study on the influence of natural fracture skins on reservoir behavior are that they have much less effect on the productivity index (PI) of a horizontal well than a skin on a well, which is considered to be because of the large differences in the skin areas through which the flows occur, as well as the adverse effect of radial compared with linear flow and the fact that matrix production from the well is not affected by the fracture skin; they lead to a small improvement in the steady-state PI of a well, which is counterintuitive (on the basis of the experience of positive skin on a well always reducing its PI); and they affect how the flux entering the fracture is distributed with distance from the well: the larger the skin, the more dispersed the flux. It is surmised the improvement in PI is associated with the reduction in local reservoir pressure gradients accompanying the reduced fluxes entering the fracture near the well. Unequal fracture skins, even with the fracture at the midpoint of the finite well, result in crossflow across the fracture over significant distances from the well.
|File Size||663 KB||Number of Pages||10|
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