Maximizing Rates And Recoveries In West Texas Natural Waterdrive Reservoirs Through Application Of High Capacity Artificial Lift Equipment
Authors: Langham Barry A. 
Published: December 2007

Abstract
Recoveries in West Texas natural waterdrive reservoirs range from 55 to 80% of the original oil-in-place. These recoveries are generally being achieved using conventional artificial lift methods in the late depletion stages. The high recovery factors and possible detrimental effects of higher capacity artificial lift have historically restricted its use in these types of fields. Contrary to general theory and operating practice, it has been demonstrated that high volume lift is an effective means of increasing rate and ultimate recovery in some West Texas natural waterdrive fields.

Introduction
Historically, operating practices in most West Texas natural waterdrive reservoirs were developed under the premise that they were so efficient that little could be done to enhance their performance. One alternative was the acceleration of recovery by increasing total fluid withdrawal rates within allowable restrictions. However, most of these fields were considered to be subject to water coning. Therefore, theoretically, increased withdrawals would increase water cut, perhaps irreversibly, and possibly reduce ultimate recovery.
With incentives of higher crude prices and the 100% market demand factor in Texas, it was decided to test this theory in some marginal high water cut producers. After significant increases in withdrawal rate, water cut remained relatively constant and in some cases even dropped. Water coning theory indicates that the added production volume should not improve recovery in homogeneous waterdrive reservoirs. If this prediction was valid, larger artificial lift in homogeneous reservoirs would not be feasible. However, based on the performance support of the few experimental high volume lift installations and the fact that real reservoirs are heterogeneous to some degree, several more installations were made. Performance of some of these additional installations is now sufficient to provide meaningful analysis and conclusions.
A post installation appraisal was used to evaluate the effectiveness of 55 high volume lift (HVL) installations in 23 West Texas natural waterdrive reservoirs. High volume lift refers to electric submersible pumps and hydraulic pumps capable of total fluid production in excess of 1000 BFPD (159 M FPD). These 23 reservoirs are located in 8 Ellenburger, 9 Devonian-Silurian, and 6 Other fields. Figure 1 is a map indicating their general geographical location. This sampling of installations investigates eight different horizons ranging geologically from the Canyon through the Ellenburger. Figure 2 depicts the relative geological position the horizons have with each other and position the horizons have with each other and their average depths.
With 3 to 48 months of post installation performance available on 55 electric submersible and performance available on 55 electric submersible and hydraulic pumps, production trends have stabilized sufficiently to estimate the incremental volume of oil which will be recovered with HVL versus conventional lift. Also, the magnitude of initial and sustained rate increase achieved with high volume lift over conventional lift is now quantifiable.
To optimize future HVL installation priority for maximum rate and recovery, the HVL analysis was subdivided into three categories. These categories are the Ellenburger, Devonian, which is a combination of Silurian and Devonian, and Other, which is composed of Abo, Canyon, Strawn, Caddo Cambrian, and Penn.

ASSUMPTIONS AND QUALIFICATIONS
Observations made as a result of this study are from HVL performance exhibited by West Texas natural waterdrive carbonate reservoirs only. Generally the installation of HVL is the final attempt to increase production and ultimate recovery.