Air Injection Into A Light Oil Reservoir: The Horse Creek Project
Authors: Germain P. , Geyelin J.L. 
Published: December 2007

Abstract
TOTAL MINATOME CORPORATION, the U.S. subsidiary of TOTAL started air injection into the Horse Creek reservoir (North Dakota, USA) in early May 1996.
The field had produced a 30 API oil under natural depletion since 1972 and production at project start-up was approximately 3 MMBBLS. Expected ultimate recovery under air injection is around 12.1 MMBBLS as opposed to 4.5 MMBBLS under natural depletion.
This paper presents the different phases of the project design and the first available production data.
The study comprised three separate phases. The first phase included laboratory work on oil oxidation properties and a thorough geological review of the field. The second phase included reservoir studies, involving numerical simulations, which were used to produce scenarii to optimize secondary production. The third phase included engineering and design of compression facilities, operational safety systems and environment protection programs.

Introduction
The Horse Creek field is located in the south-central portion of the Williston Basin, Bowman County, North Dakota (Figure 1). The field is a stratigraphic trap and consists of fifteen oil wells.
The Horse Creek field was discovered in November, 1972 with the completion of the Carl Olson 1–13. The Carl Olson 1–13, followed by the Comtrust 14–13, remained the only productive wells until 1981. From June 1981 to December 1988, 13 producers and five dry holes were completed within the Horse Creek field area.
Secondary recovery potential of the field has been evaluated jointly by Total Minatome Corporation (TMC) and TOTAL (Paris) since May 1993 by conducting geological, lab evaluation and reservoir modeling studies of the field. Based upon the encouraging results of these studies, Total Minatome Corporation formed a secondary recovery unit for the Horse Creek field in November of 1995 for an air injection project. TMC currently operates eleven producing wells, three air injection wells, one monitor well, and one water disposal well within the field area. Producing well spacing is approximately one well per 320 acres.
Six months after air injection start up preliminary results are encouraging as production has increased by more than 10%.

GEOLOGY
The Horse Creek field is a stratigraphic oil accumulation in the Red River Formation of Ordovician age. The upper portion of the Red River Formation consists of a series of brining upward, cyclic carbonates, deposited in a subtidal to supratidal environment on a restrict shelf during the Red River marine transgression.
The upper portion of the Red River formation is composed of limestones, dolomites, and anhydrites Lithology varies from laminated mudstones, to heavily bioturbated packstones, wackestones, and mudstones. Several stages of syn and post depositional dolomitization of the heavily bioturbated units, have resulted in secondary porosity from which the Horse Creek field produces.
The upper portion of the Red River formation, in this portion of the Williston Basin, is subdivided into four porosity zones. These porosity zones are referred to as the "A" through "D" zones.
Oil production in the Horse Creek field occurs from the Red River "D" zone from heavily bioturbated packstones, wackestone, and mudstones. Core data indicates that the major production from the "D" zone occurs from the subtidal, heavily burrowed mudstones, found in the middle to lower interval of the "D" zone. P. 233^