On the Feasibility of Pressure Relief by Water Removal During Development and Operation of Gas Storage in Aquifers

Abstract

This paper was prepared for presentation at the 47th Annual Fall Meeting of the Society of Petroleum Engineers held in San Antonio, Tex., Oct. 8–11, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by who the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract In this paper, simulation studies together with actual field data are used to show that much water is unnecessarily confined in the interwell space as a result of the conventional multi-well injection operations in aquifer gas storage. Reasons are given for the universally observed difficulty in increasing the thickness of the gas bubbles. it is shown that, after many years of development and operation, the average gas saturation of the invaded pore space has limiting values closer to 50 percent rather than the 70–80 percent expected by undeserved reliance on the full gravity segregation of gas and water. To overcome the problems stated above, the authors recommend the use of pressure relief by water pumping during the development phase of aquifer storage in moderate-to-low permeability, relatively thin formations. The purpose is to:increase early injection volumes for faster development,reduce the inefficient invasion of the aquifer by the gas front,increase the gas saturation of the interwell space to optimize storage space per unit bulk rock, andincrease well deliverability. Introduction Due to the increasing importance of natural gas, thereby leading to its shortage, econo-political pressures are mounting to reduce or eliminate entirely the large interruptible loads and to provide gas only to the higher end use customers. This trend toward conserving gas for the premium paying customers, such as residential space heating, will produce new requirements for additional gas storage capacity. In order to meet this additional demand, one of the important sources of storage capacity - aquifer storage - will have to be developed faster and more efficiently than ever before. After a suitable aquifer structure has been obtained, it should be noted that there are two major complications which will retard the development of an adequate storage facility — 1) the difficulty in obtaining reasonable gas saturations together with insufficient bubble thickness in the desired zone, and 2) the premature "watering out" of the producing wells. When multi-well gas injection patterns are used in developing gas storage, especially in layered or relatively thin aquifers, excessive amounts of water remain confined within interwell space. Also, field experience shows the gravity segregation between gas and water to be much less significant than was expected at the outset. In many storage reservoirs, the observed gas bubble thickness stabilizes rapidly or increases very little with time, whereas thickening was expected due to gravity drainage.