Performance of Sharon Ridge Canyon Unit with Water Injection
Authors: Stiles L.H. , Clay Terry , Vestal W.A. , Waid J.B. 
Published: December 2007

Although this waterflood had performed beautifully for fifteen years, a detailed geologic and engineering study revealed that if all areas of the unit were to be depleted efficiently the peripheral injection pattern would have to be modified. The moral: keep a gimlet eye on that flood; its beauty may be only skin deep.

Introduction
The Sharon Ridge Canyon Unit is located about 20 miles southwest of Snyder, Tex., and is one of several major oil fields producing along the Horseshoe Atoll trend of Pennsylvanian and early Permian age. Production is from a common reservoir with the Production is from a common reservoir with the SACROC and Diamond "M" Units. R. E. Smith is operator of the unit, which contains 13,712 acres and includes 344 wells producing from an average depth of 6,800 ft. Cumulative oil production through 1970 was 120 million bbl since discovery and cumulative water injection was 202 million bbl since unitization. The field's primary performance and early unit history were reported in 1961.
The Sharon Ridge Unit is a good example of conservation and foresight by the working-interest owners: in 1951. only 2 years after discovery and at a time when the field was only 75 percent developed, an engineering committee recommended unitization with water injection to increase the ultimate recovery. Although the unit did not become effective until 1955, the field was still producing top allowable with little free gas saturation and a relatively low GOR at the time water injection was begun.
Unit Performance Injection Pattern
A peripheral water injection pattern was selected initially for the following reasons:
To contain as much of the reservoir oil aspossible within the pattern area. To keep the initial investment low by using aminimum number of injection wells. To allow high-productivity wells located in thethick, central part of the reef to be the terminalproducing wells in the unit.
Initial injection was into 22 wells located along the periphery. Later this number was increased to 39. To prevent oil migration, offsetting injection throughout the oil zone was maintained along the common boundary between the Sharon Ridge and Diamond "M" Units. All injection wells on the periphery were deepened approximately 50 to 100 periphery were deepened approximately 50 to 100 ft below the oil-water contact. Implied in a pattern of this type is the requirement that there be a significant amount of vertical as well as horizontal permeability in order for water injected below the permeability in order for water injected below the oil-water contact to be effective throughout the oil zone as the waterfront moves inward toward the center of the reef. Estimates of vertical continuity may be made from log and core data; however, only observation of actual performance can determine whether sufficient vertical continuity exists to permit efficient waterflooding.

Unit Production and Recovery
In general, unit performance has been very good, with an indicated ultimate recovery exceeding 50 percent of the original oil in place. percent of the original oil in place.
JPT
P. 431