ABSTRACT
A horizontal well can be several times more productive than a vertical one draining the same volume. Recent interests have been accelerating because of improved drilling and completion technologies. This has led to increased efficiency and economics in oil recovery. However, it is more expensive to drill a horizontal well than a vertical one. Therefore, to determine the economic feasibility of drilling a horizontal well, engineers need to be able to estimate its expected productivity. The productivity - which is the ability of a reservoir to deliver the fluid to the wellbore – is represented by the productivity index.
Several parameters such as the length of the horizontal wellbore (L), reservoir drainage area (A), pay zone thickness (h), wellbore radius ( skin (s), well completions, fluid viscosity (µ) etc. affect the productivity index of horizontal well.
This study considers the effect of skin and wellbore radius on the PI of a horizontal well for an isotropic infinite acting reservoir. Using a PI equation for an infinite acting reservoir with standard formation and fluid parameters, this study presents the effects of the varying well radius and skin on the productivity index. Comparing the inverse relationship between increasing wellbore radius and positive skin as well as that of the varying wellbore radius and decreasing negative skin to productivity index, this study finds that Increasing wellbore radius as well as an increasing value of skin, reduces the productivity index.
The results of this study can aid the production engineer in selecting the best completion method to employ for the optimum recovery of reservoir fluids
