Review Of Secondary Recovery Operations In The Greater Aneth Area, San Juan County, Utah

Abstract

Abstract Secondary recovery operations presently being conducted in the Greater Aneth Area, San Juan County, Utah, are reviewed. Early in the development of the reservoir it became apparent that initial primary recovery would be a small percentage of the total oil in place. It was concluded by the operators that waterflooding would be the most satisfactory method of secondary recovery. Although it is too early in the life of the flood to substantiate, present estimates indicate that the ultimate recovery of oil will probably be twice the recovery anticipated from the original solution gas drive mechanism. Primary recovery has almost been completed and future production will be the result of waterflooding. In addition to the increase of oil recovery, over-all economics will be enhanced by the 80-acre well spacing now in effect. Introduction In April 1956, Texaco, Inc. completed the Navajo "D-1" which was the discovery well in what was to become one of the largest fields in the Rocky Mountain Area, the Aneth Field. During the next four years over 600 wells were drilled which delineated a productive area in excess of 55,000 acres with an estimated reserve around one billion barrels of stock tank oil in place. Primary recovery was calculated to be approximately 14.3 to 18.5 percent, and secondary recovery resulting from waterflooding was estimated to increase the initial recovery an additional 12 to 14 percent. It is the purpose of this report to review both the background considerations relating to secondary recovery and its' progress to date. GEOLOGY The Aneth Field, later called the Greater Aneth Area, is located in the Utah portion of the Four Corners Area, see Fig. 1. Geologically the field is located on the Southwestern flank of the Paradox basin. The basin covers parts of Utah, Arizona, Colorado and New MEXICO. Production is from carbonates at a depth between 5,300 ft. to 6,200 ft. in the Paradox Formation which is middle Pennsylvanian in age, specifically, the Desert Creek and Ismay zones of the Paradox. The Desert Creek zone is better developed and more continuous over the area and contributes around 90 percent of the hydrocarbons. This zone is further divided into three subzones of which only the upper two are significant. The field can be described as a reef complex with structure playing a minor role in accumulation. Reservoir development and porosity are due to fossiliferous deposition with some mineral solution activity and a highly varying fracture system. The productive area is surrounded by shales and reworked, non-porous, clastic carbonates in a somewhat circular area about 10 miles in diameter. RESERVOIR CHARACTERISTICS The primary producing mechanism for the reservoir is solution gas expansion. Original bottom hole pressure was 2200 psi at 900 ft. subsea. General core and fluid analysis are shown in the following tabulations: Approximate height of oil column.............250 ft. Average permeability......................... 20 ft.