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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.


This paper presents an experimental study of linear unsteady state gas flow through a low permeability porous medium. Results of a series of controlled tests indicate that a steady state approximation technique for the solution of linear unsteady state gas flow is the most accurate and convenient method. s tests confirm the validity of using finite difference equations for solving the nonlinear partial differential equation for the unsteady state gas flow. Also the results these tests indicate that the modified solution of the partial differential equation relating slightly compressible fluid flow does not represent gas flow in a low permeability porous medium.


The investigation of unsteady state gas flow has been restricted almost entirely to mathematical analysis. Basically, there are three types of solutions which approximate gas flow:

  1. The first method is a modified solution of the differential equation representing slightly compressible fluid flow. Certain critical assumptions are used to force the liquid solutions to exemplify gas flow.

  2. For the second type of solution, finite difference equations are used to represent and solve the non-linear partial differential equation for gas flow.

  3. The most recent analysis of transient gas flow involves forcing the steady state flow equation for gas to predict pressure decay with time.

Since all three types of analyses are not true solutions to the differential equation relating gas flow in porous media, they are restricted to certain limiting assumptions and methods of calculation. For example, method number one has the limitation that small pressure drawdowns must occur in the reservoir. In the case of low permeability formations, this is almost an impossibility.