Successful Prediction and Performance in Waterflooding Wesson Hogg Sand Unit
Authors: Clanton Hoyle W. 
Published: December 2007

The Hogg Sand Unit, operated by McAlester Fuel Co., was discovered in Jan., 1946. This highly porous and permeable reservoir is one of nine productive zones in the Wesson field, Ouachita County, Ark. Unitized operation became effective on July 1, 1948, and water injection was initiated on Sept. 1 of that year into two input wells with other wells being converted to input service as the field developed and the unitized area extended. Response to water injection was obtained in measurable quantities within less than 6 months. Reservoir fill-up was obtained during 1951; at that time oil production had reached a peak of 7,000 B/D. Ultimate recovery was originally estimated at 29,787,000 bbl or 1,000 bbl/acre-ft. Secondary recovery was projected to approximate 29.4 percent of the oil in place as compared to a primary recovery of 17.6 percent for an estimated ultimate recovery of 47 percent. Actual performance has exceeded this predicted performance during the 18 years of unitized operations. Cumulative recovery as of July 1, 1966, amounts to 30,773,000 bbl for a recovery of 1,035 bbl/acre-ft or 103.5 percent of the original estimated recoverable reserves. Current production is obtained by natural flow from 19 wells and averages 1,700 B/D with a field-wide water cut of 90 percent of total fluid. From a projection of the indicated decline, an additional recovery of 2,000,000 bbl is anticipated which would yield an ultimate recovery of 1,103 bbl/acre-ft.

Introduction

The Hogg Sand reservoir of the Wesson field is located approximately 1/2 to 2 miles east and south of the town of Stephens in Ouachita County, Ark., and covers parts of 11 sections in Township 15 South, Range 19 West. The desirability for operation of this reservoir under pressure maintenance became apparent soon after its discovery when declining reservoir pressure and production gave evidence of a typical solution gas drive recovery mechanism. An analysis of the reservoir and its predicted performance under primary recovery and under gas or water injection was made by an independent consulting engineering firm. This analysis revealed that a recovery of 378 bbl/acre-ft could be expected by natural depletion, while gas injection would increase recovery to 800 bbl/acre-ft and water injection would recover 1,000 bbl/acre-ft. Individual operators unitized their leases, effective July 1, 1948, for the purpose of conducting secondary recovery operations by waterflooding. This project has many characteristics similar to other floods, with these unusual exceptions:

- introduction of water into the reservoir began almost a full year before the field was fully defined and developed;

- the flood pattern conforms to none of the general patterns in use and is defined as an irregular segmented line pattern;

- producing rate has been controlled by proration from inception to the beginning of 1962 when a capacity rate was established; and

- operation of the reservoir at near its original pressure of 1,300 psi with artificial lift was practiced until 1959 when the pressure was increased to 1,600 psi to flow all production and minimize operating costs.

Despite the increased backpressure against the formation, no detrimental effects have been apparent in reservoir performance. Proration in a waterflood and a wide range of reservoir pressures are departures from the generally accepted practice, and serve to point out that flexibility does exist in waterflood projects a blanket policy of procedure does not exist. It must be emphasized that the excellent formation and fluid characteristics are the factors which enabled such procedures to be successful in this project and would not be applicable in reservoirs where these factors are of poor quality.

Geology and Reservoir Chracteristics

The sand under flood is known as the Hogg sand, which is part of the basal Pine Island formation of Lower Cretaceous age. It is a submarine bar-type deposit which occurs at a subsea depth of 2,900 ft, or approximately 3,150 ft below the ground surface in this area. Though it is highly porous and permeable, the sand quickly grades to shale at the edges of the reservoir and is limy near its base.