Skull Creek Newcastle Sand Unit - A Successful Polymer Flood
Authors: Janeczko Michael A. 
Published: December 2007

The Skull Creek Newcastle Sand Unit is located in the northeast corner of Wyoming's Power River Basin. A Dow 500 polymer injection program was carried out in the Cretaceous Newcastle Sandstone reservoir from March of 1974 to November of 1978. A discussion of flood operations, reservoir analyses and economics indicates that this polymer flood was very successful.

Introduction

The Skull Creek Newcastle Sand Unit is located in the northeast corner of Wyoming on the eastern edge of the Powder River Basin. This 3,000 foot (914. m) deep Newcastle Sandstone Reservoir was originally drilled in 1949. It was unitized in August of 1969, with Texaco Inc. as the 95.4% working interest owner and operator. Waterflooding operations were begun in January of 1970. The waterflood unit is a 1,040 acre peripheral pattern which was modified with some infill injectors to more completely sweep certain areas of the reservoir. Current unit production is 340 barrels (54 m3/d) of oil per day.

In October of 1970, the Society of Petroleum Engineers published a paper entitled A Progress Report of Polymer Flooding Skull Creek South Unit, Weston County, Wyoming. This paper outlined the results of a small scale Dow 520 Pusher Polymer Flood which was completed in the Newcastle Sandstone Reservoir by the American Petrofina Company of Texas in 1969. This field is located just southwest of Texaco's Skull Creek Newcastle Sand Unit.

A thorough analysis of this flood and another polymer flood to the north, operated by McAlester polymer flood to the north, operated by McAlester Petroleum, was done by Texaco personnel in 1972. Petroleum, was done by Texaco personnel in 1972. This analysis indicated that these polymer floods were very successful, with the Petrofina flood reaching an average of 63% increased recovery efficiency over conventional waterflooding.

Limited coreflood testing was performed in 1973 at Texaco's Bellaire Laboratory using Calgon 454 Polymer in core material from the Skull Creek Unit. Polymer in core material from the Skull Creek Unit. Although these tests were very limited, and somewhat inconclusive, the Bellaire Laboratory recommended that due to the extreme vertical permeability variation in this reservoir, some benefits could be gained from polymer flooding the Skull Creek Field. Adverse oil-water mobility ratio, low reservoir temperature, low salinity, high regional permeability variation, and poor vertical distribution of injected fluid also indicated that the Skull Creek Newcastle Sand Unit was an excellent candidate for polymer flooding.

Based on these facts, together with the apparent polymer flooding success of the other operators, polymer flooding success of the other operators, a 20% pore volume injection schedule was set up and the polymer project was initiated on March 13, 1974 with the addition of Dow 500 Polymer to the injection water at SCNSU.

FIELD OPERATIONS

The injection system consists of one main injection plant which distributes water to five satellite manifolds through four-inch steel lines. The lines from the manifold stations to the wells are all two-inch 2,000 psi (13,790 kPa) fiberglass. Figure I shows a field map of the injection system.

The polymer injection skid is located in a building next to the water injection plant. All produced water from the treaters is dumped into produced water from the treaters is dumped into the surge tank at the injection plant where make-up water from a Dakota supply well is added to the 2,000 bbl/D (318 m3/d) injection stream. An eight-inch line comes out of this tank right into the suction of the Continental A125M injection pump. A two-inch line draws about 400 bbl/D (63.6 m3/d) of fluid out of this tank which cycles through the polymer unit where the Dow 500 dry polymer is mixed polymer unit where the Dow 500 dry polymer is mixed into solution. This solution is then pumped back into the suction line to the main injection pump. This low-pressure operation greatly simplifies the polymer addition process and is one main advantage polymer addition process and is one main advantage of using Dow's dry polymer feeder system.