Development of horizontal well technology offers a new approach to reducing gas/water coning effect during oil production. However, further improvement of the oil production rate of horizontal wells is still limited by the encroachment of the water cone when bottom water exists. This paper provides reservoir engineers with a general solution of the gas/water coning problem for horizontal wells. The objectives of this investigation include: (1) to determine the location of the stable water/gas cone, (2) to estimate the critical oil production rate, and (3) to find out the optimum placement of the horizontal wellbore so that the maximum critical oil rate can be obtained.

Using conformal mapping method, the location of the stable water/gas cone is determined as a function of oil rate and wellbore location. The critical oil rate is estimated by examining the profile development of the stable cone. It is found that the critical rate is directly proportional to the effective permeability (khkv), thickness of the oil reservoir, and density contrast between oil and the coning fluid, and inversely proportional to the oil viscosity. The critical oil rate also depends upon the wellbore location in the oil reservoir and takes its maximum value when the horizontal wellbore is placed at about 70 % of reservoir thickness from the unwanted fluid.

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