Kenji Furui's thesis
by
Kenji Furui, MSE
University of Texas at Austin, 2001
Supervisor: A. Daniel Hill
The skin equation presented here can take reservoir anisotropy and
damage heterogeneity into account. The description of cross sections of damage
normal to the well is based on the pressure equation for an anisotropic medium,
which is most likely circular near the well and elliptical far from the well. This
assumption gives an appropriate skin factor even for a small penetration of
damage while the existing skin models sometimes give a negative skin for a
damaged reservoir.
We also proposed the productivity index ratio equation for a damaged
rectangular reservoir. This equation clearly states that the ratio of the reservoir
height and drainage length perpendicular to the well may be very important for
estimating the influence of formation damage on horizontal well productivity
because the linear flow geometry becomes dominant for a thin reservoir.
In examples, a truncated elliptical cone with the larger base near the
vertical section of the well is presumed to compare the model with the existing
damage model. However, our skin model can be applied for any damage
distribution along a well. This model could be a powerful tool when the
distribution of damage is very complicated and when the skin equation is difficult
to solve analytically. In addition, it can be easily coupled with several kinds of
reservoir inflow models. The impact of formation damage on the overall
production is also shown in examples. As many authors discussed, the skin effect
for a horizontal well completion is comparatively small for many cases. However,
if the reservoir height is large, the radial flow becomes dominant and the skin
effect in a horizontal well is more likely to be the same as that in a vertical well.
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