Computing the Movement of Injected Raw Helium in Bush Dome Reservoir

Abstract

Conservation helium stored in the Bush Dome reservoir displaces native gas under pressure. A computing program simulates the movement of stored helium in response to variations in the composition of the gases and to variations in structure thickness, permeability, and porosity. Despite some possible adverse factors, injected helium can be maintained in a compact mass so that through judicious control of flow rates it can be recovered efficiently. Introduction The storage of helium-gas mixtures under the U. S. Bureau of Mines helium conservation program was begun Jan. 5, 1963, more than 40 years after a plant near Fort Worth, Tex., first produced refined helium in commercial quantities, and approximately 4 years after it was demonstrated that raw helium could be recovered from a natural underground-storage reservoir. In 1960, Congress recognized that helium was a valuable and irreplaceable resource and passed legislation enabling the Secretary of the Interior to enter into long-term contracts for the purchase of helium for storage. Plants of private companies under contract and government plants have provided 38.8 Bscf of approximately 70-percent raw helium for storage in the Bush Dome reservoir near Amarillo, Tex., in the period ending with 1970. The Bush Dome reservoir is an anticline in the Brown dolomite of the Permian-Wichita-Albany formation at a depth of about 3,300 ft. Anhydrite and shale stringers in the dolomite are evident in every well, but individual stringers cannot be correlated between wells. Porosity based on core analyses ranges from 4 to 20 percent, and the average porosity to gas is 7 percent. A fixed water table constitutes the floor of the reservoir, and the maximum net thickness of the gas-bearing structure at the principal dome is 368 A. The caprock is the Panhandle lime formation and consists largely of impermeable anhydrite about 400 ft thick. At the time of field discovery in 1924, reservoir pressure was about 815 psia. When the conservation program began, a net total of 53 Bscf of native gas had been removed, so that the pressure was lowered to 685 psia. Reservoir temperature is 92 degrees F. The storage operation was planned to continue about 22 years. In the early years, net flow of the four injection wells on the crest of the structure and 20 outlying recovery wells was such that reservoir pressure increased gradually. Since it is the policy pressure increased gradually. Since it is the policy not to exceed the original field discovery pressure at injection wells, native gas being displaced must be withdrawn from recovery wells at approximately the rate that raw helium is injected. One problem is that recovery wells near the injection wells eventually are invaded by injected raw helium and must be shut in. Of necessity such invasions will continue to occur. Moreover, it is important that the injected raw helium not be unnecessarily dispersed in the formation. As a means of controlling these phenomena, a mathematical model was developed. Its purpose was to provide information for determining the effective relative flow rates of wells and to determine where to locate the new wells required for optimal execution of the conservation program. This paper concerns the storage operation and the problems of guiding it by means of the computing problems of guiding it by means of the computing program. Nearly 8 years of actual storage history are program. Nearly 8 years of actual storage history are simulated. JPT P. 16