Sheep Mountain CO2 Production Facilities - A Conceptual Design
Authors: Renfro J.J. 
Published: December 2007

This paper discusses the potential supply of CO2 for enhanced recovery projects from the natural CO2 reservoir at Sheep Mountain, Huerfano projects from the natural CO2 reservoir at Sheep Mountain, Huerfano County, CO. Producing well characteristics are examined, and a conceptual process is discussed for separation of water, dehydration, compression, and transportation of 300 MMscf/D of CO2 from Colorado to Texas.

Introduction
Carbon dioxide (CO2) enhanced recovery projects potentially could recover up to 40% of all oil produced by potentially could recover up to 40% of all oil produced by enhanced recovery methods. CO2 supply is a critical factor in the ability to undertake the scope of available projects. The major sources of supply include power projects. The major sources of supply include power plant stack gas, future coal gasification plants, and plant stack gas, future coal gasification plants, and natural deposits. Although power and coal gasification plants eventually may be important sources, natural plants eventually may be important sources, natural deposits likely will be the first source to be developed.ARCO Oil and Gas Co. began studies of a natural CO2 reservoir at Sheep Mountain in Huerfano County, CO, in 1972. These studies resulted in lease of private, state, and federal lands and the formation of two development units, Sheep Mountain Unit and Dike Mountain Unit (Fig. 1). Sixteen wells within these units have delineated a deposit of sufficient size to warrant a pipeline study. Given sufficient incentive for enhanced oil recovery, ARCO Oil and Gas Co. could build a 20-in. pipeline 420 miles to the Permian basin to deliver 300 MMscf/D. The proposed route shown in Fig. 2 terminates at the Wasson (San Andres) and Seminole (San Andres) fields located in Yoakum and Gaines counties, TX.
Pipeline Pipeline The pipeline would begin in the northwestern portion of Sheep Mountain Unit at an elevation of 8,000 ft and continue southeast near Trinidad, CO, where it would drop to an elevation of 5,400 ft. The line would climb to an elevation of 8,250 ft east of Raton Pass before continuing southeastward across New Mexico and into Texas to the Seminole field at an elevation of 3,400 ft.The pipeline would operate as a liquid-filled system requiring sufficient pressure throughout the line to prevent two-phase (gas/liquid) occurrence and an input prevent two-phase (gas/liquid) occurrence and an input pressure exceeding 1,200 psig. CO2 density at various pressure exceeding 1,200 psig. CO2 density at various pipeline operating conditions can vary from 44 to almost pipeline operating conditions can vary from 44 to almost 60 lbm/cu ft; therefore, the differences in elevation involve significant head changes. Two-phase conditions would be approached at the maximum design rate of 300 MMscf/D where the line rises to 8,250 ft, resulting in the lowest line pressure of approximately 950 psig. Two-phase conditions would be approached more closely in late summer as the flowing temperature peaks, perhaps approaching 75 degrees F. The 8,250-ft location also would be critical to winter operating conditions because of the reduced ability of the CO2 to hold water at low temperature and pressure. One criterion for pipeline corrosion control is for the CO2 to have a water content less than 60% of saturation. Thus, the 8,250-ft elevation mountain crossing establishes the required input line pressure and the degree of dehydration required of the producing equipment.Desired pipeline delivery pressure is approximately 2,000 psig, which is sufficient for field distribution and injection control. The pipeline is sized to facilitate this delivery pressure at 300 MMscf/D without booster compression along the line.
JPT
P. 1462