This paper was to be presented at the 40th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Denver, Colorado, October 3–6, 1965, and is considered to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Technology or the Executive Secretary. Such abstract elsewhere after publication in the Journal of Petroleum Technology or Society of Petroleum Engineers Journal is granted on request, providing proper credit is given that publication and the original presentation of the paper.
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.
During recent years, the increase in contract prices of natural gas and in its value to the oil operator, have provided the incentive to improve reservoir recovery of this material. Secondary recovery of natural gas will be limited to those parts of the world where its value is several times the value of some other high-pressure gas. High-pressure gases suitable for the recovery of natural gas include air, nitrogen, carbon dioxide, exhaust gases, and some low-value natural gases. The application of current miscible displacement techniques can result in the recovery of one-half of the natural gas normally remaining in a reservoir at abandonment.
During the many years when natural gas was produced as a by-product of oil productions its value was largely ignored. In many cases large volumes of natural gas were flared with no effort being made to conserve this valuable material. Only a slight improvement was realized when many of the first sales contracts were written for ridiculously low prices. Until recently, large volumes of natural gas were sold for less than the cost of compression to the sales pressures. Such contracts completely ignored the intrinsic value of this high-quality fuel. This poor situation was made worse when these distress prices were recognized by a federal regulatory body as proper price levels for natural gas moving in interstate commerce.
The production of natural gas from a reservoir is inherently more efficient than the production of oil from a reservoir. In volumetric reservoirs, at moderate depths with high formation permeabilities, recoveries of 90 per cent of the gas originally in place are common.
In many other cases, high recoveries are not attained. In reservoirs with low permeabilities, the producing rates may fall below the economic limit while large portions of the original gas are still in the reservoir. The minimum economic gas production rate is raised by the production of liquids or by any other difficulties which tend to increase operating problems and expenses. In reservoirs with strong water drives and unequal water invasion, large amounts of gas may be lost in the residual gas saturation or by premature watering out of the producing wells. In such cases, the recovery of the gas originally in place may be as low as 50 per cent.
In the past, such high losses of natural gas were not as important because of the low sales prices. As with any other resource, the amount of gas which may be economically recovered is a function of its value.