Clay Basin Storage Project-Development Of A Nearly Depleted Gas Reservoir To Gas Storage
Authors: Baird James L. 
Published: December 2007

Abstract
A study of the Dakota formation in the Clay Basin field determined the potential gas storage capabilities and the level of development required to provide gas storage service. In general, this paper discusses the steps involved from analysis of the potential of the Dakota formation for gas storage to full operation status. Emphasis is placed on the use of a two-dimensional, single-phase, dry gas reservoir simulator in studying the Clay Basin field. Also discussed is the timing of development of the project, the facility requirements and changes in operational planning based on actual performance of the project to date. Additional comments are made on the first season usage problems in obtaining reservoir performance data to be problems in obtaining reservoir performance data to be used in future operational planning and project development studies.

Introduction
The underground storage of natural gas has become an essential part of many utility companies' gas supply strategy. Companies must meet annual contractual requirements with producers and maintain reliable service to the high priority residential and small volume consumers of the nation during peak demand periods. The Clay Basin field, located in Daggett County, periods. The Clay Basin field, located in Daggett County, Utah, is of particular interest to the Rocky Mountain area as a guide for the potential development of other reservoirs for gas storage service. Mountain Fuel Resources, Inc., a wholly-owned subsidiary of Mountain Fuel Supply Company, acquired the necessary right from Mountain Fuel Supply Company to develop and operate the Dakota formation to provide storage service for interested parties.

DESCRIPTION OF STORAGE PROJECT
The Clay Basin field is located in northeastern Utah (T3N-R24E) on the north flank of the Uinta Mountains. The town of Rock Springs, Wyoming is 50 miles to the north, and Salt Lake City, Utah is approximately 140 miles to the west, as shown in Figure 1. Gas is stored in the Dakota sand which lies about 5,800 feet below the surface. Surface elevations range from approximately 6,275 feet to 6,675 feet above sea level.

GEOLOGY
Regionally, the Clay Basin field is located on the north flank of the Uinta Mountain Arch and on the extreme southern margin of the Greater Green River Basin of southeastern Wyoming and northeastern Utah. Regional dip is north into the east-west trending Red Creek Syncline. Locally, the Clay Basin field produces from a northwest-southeast trending symmetrically developed doubly plunging anticline. Structural closure of the Dakota storage zone consists of 300 feet.
The Clay Basin Anticline is bordered on the north and south flanks by two major faults. The north bounding fault is a high angle reverse fault striking northwest to west. Seismic data, geologic surface mapping and well control indicate an apparent displacement of approximately 2,400 feet. The south bounding Uinta fault is also a high angle reverse fault with an apparent throw of more than 18,000 feet trending in an east-west direction. Figure 2 is a structure map on the top of the Dakota formation. (Note that the contours are elevations above sea level)
Overlying the Dakota storage zone is the Mowry shale, approximately 160 feet thick, providing an excellent caprock. The Mowry shale is between the Dakota storage zone and the currently producing Frontier sand. Pressure performance through the producing history of the Dakota and Frontier reservoirs demonstrate the integrity of the Mowry shale as a reliable caprock.

DEVELOPMENT HISTORY OF THE DAKOTA FORMATION
Originally, the Clay Basin field was discovered by Producers and Refiners Corporation in April, 1927 when significant quantities of natural gas were encountered by the Unit Well No. 1 (originally R.D. Murphy Well No. 1), in the Frontier formation. In 1935, subsequent drilling by Mountain Fuel Supply Company confirmed commercial quantities of natural gas with the Unit Well No. 2 in the Dakota formation. This well had an initial open-flow potential of 32,000 Mcf/day and a shut-in surface pressure of 2200 psig. By the time the field was connected to the Mountain Fuel Supply Company mainline in July, 1937, two Dakota wells had been completed and two wells were drilling.