Investigation of gas and water coning behavior for the enhancement of oil production |
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Authors: | Woo Cheol Lee Young Soo Lee Ki Hong Kim Kye Jeong Lee Won Mo Sung Jinsoo Kim |
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Affiliation: | (1) Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY, USA;(2) Enhanced Oil Recovery Institute, University of Wyoming, Laramie, WY, USA |
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Abstract: | This study presents the extensive simulation to control the concurrent behavior of gas and water coning in oil reservoir with
existence of a bottom aquifer. From simulation results, coning phenomena were observed even with the critical oil rate obtained
analytically. It is because the critical rate is calculated using a steady state expression. In order to examine the coning
behavior, firstly, we have run for various oil layer thicknesses. The result in case of thin layer shows early breakthrough
of gas and water cones and the increase in water-oil ratio from the beginning of production. Meanwhile, for the thick case
of 200 ft, there is no water breakthrough observed even though water cone has been already formed because it is stable. Since
gas and water cones move mainly in a vertical direction, cone development is affected by a vertical permeability. As a result
of runs for vertical permeabilities, the breakthrough time is getting delayed as the vertical permeability is smaller. In
the case of a high vertical permeability, the shape of the water cone is developed in a concave form at the beginning. After
two years of production, however, this cone shape becomes almost flat since the water-oil contact is elevated uniformly throughout
the whole reservoir. In the analysis of coning behavior for different aquifer sizes, it is found that the aquifer size does
not affect both cone shape and watercut. But with a strong bottom aquifer the behavior of gas coning is greatly decreased
since the pressure is maintained by the active aquifer. The extent of well penetration into the oil layer has a considerable
effect on coning phenomena. As the completion interval is decreased, the breakthrough time is delayed. However, a large pressure
drop occurs in the shortest interval so that it worsens the well productivity. The most practical method to control coning
is the oil production rate. Production of gas and water can be minimized by keeping oil rates as low as possible. However,
a low rate is directly linked to well’s economics, and therefore, the optimizing process for the production rate is essential. |
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