A heterogeneous carbonate reservoir displaying a characteristic sequence of high permeability layers above low permeability layers and undergoing peripheral waterflooding, a non-uniform flood front usually develops. Oil in the tight facies is normally trapped or bypassed when water preferentially sweeps the upper clean facies. Recovery of this bypassed oil is often complicated by the presence of overlying water. With the advent of horizontal well technology, the question arises as to whether or not this new technique can improve the recovery from these heterogeneous reservoirs.

This paper examines the use of a horizontal well and compares the result to that of a vertical well in the type of reservoir described above. A 3-0 simulation model was constructed of a localized area within the reservoir. Vertical and horizontal wells were simulated in separate cases of decreasing vertical permeability between the permeable and the tight zones. Model runs were also made with varying layer locations for the horizontal well.

Results indicated that horizontal wells in the tight facies recovered no more oil from the dirty than a vertical well penetrating the entire reservoir thickness. Furthermore, the horizontal well in the tight facies recovered the same percentage of permeable to tight as a horizontal well completed in the clean facies. The only difference being the earlier, higher recovery from the respective layer in which the horizontal well is completed. This behavior is explained by the fact that severe cross flow from permeable to tight existed. This cross flow persisted down to vertical permeability values of .0001 millidarcy.

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