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Abstract

Horizontal drilling for primary oil recovery has become a routine practice in some areas of the United States, with more than 2,700 wells drilled nationwide averaging horizontal extensions of 1,500 to 3,500 feet. Frequently these wells are targeted for achieving a near perpendicular intercept with natural fracture systems in reservoirs having a substantially vertically fractured matrix. Many such horizontal wells have resulted in oil production rates more than sufficient to payback the higher well expense in as short as a few weeks. This rapid payout has provided the incentive for drilling additional horizontal wells, thus advancing horizontal well drilling technology. It would appear that horizontal wells may also find application in certain secondary or enhanced oil recovery projects. Primarily for this reason, a reservoir modeling study was performed to determine the possible use of horizontal wells to optimize the performance of such projects. From the study it was learned that both the length and the orientation of horizontal wells have a very significant effect on the areal sweep efficiency of commonly utilized oil displacement processes; sweep efficiencies ranged from near zero percent to almost one hundred percent of the pattern area and were found to be dependent primarily upon the well length and orientation. The incremental costs of drilling horizontal wells were investigated in combination with the projected increase in oil recovery over vertical wells. The economics of horizontal wells for improved recovery were then evaluated and found to be highly attractive when the horizontal legs were favorably oriented.

Introduction

Horizontal drilling for primary oil recovery has become a routine practice in some areas of the United States, with more than 2,700 wells drilled nationwide. The vast majority of horizontal wells in the United States have been drilled between the depths of 5,000 and 15,000 feet, and with horizontal extensions typically ranging between 1,500 and 3,500 feet. Most have been drilled into reservoirs having a substantially vertically fractured matrix pay zone, with the objective of achieving as many intersections between the horizontal well and the highly conductive natural fractures as possible.

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