A 1966 Critique on Pressure Transient Testing
Authors: Rodgers John S. , Garb Forrest A. 
Published: December 2007

Rodgers Jr., John S., Member AIME,

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. 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 whom 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.

Pressure transient tests when properly conducted and interpreted, offer valuable information to any exploration, development or production venture. Determinations of hydrocarbon volume initially in place, stabilized reservoir pressure, distance to a reservoir rock or fluid discontinuity, distance to impermeable barriers, extent and orientation of a fracture system, porosity-thickness, completion efficiency, formation damage and permeability-capacity are often obtainable from one or more of the various types of pressure transient tests.

Knowledge of these factors when considering alternate investment opportunities can enable prudent decisions.

A pressure transient is a pressure gradient or disturbance created by altering the equilibrium of a reservoir system. This occurs not only when new wells are completed, but each time the flow rate of a producing well is altered. In pressure transient can be analyzed to reveal the above factors. The mathematical analysis can be facilitated if the transient is established under controlled conditions. Transient tests are usually designed to meet the requirements imposed by the mathematics describing fluid flow through a porous media for the reservoir system being considered. For the purposes of this paper, only radial systems are discussed because they have the most application.

A pressure transient test in a hydrocarbon reservoir has been compared to throwing a stone in a pond of water. When a stone hits the water ripples move out radially at a fixed rate contingent on the environmental conditions. The size of the stone will affect the amplitude of the transient but amplitude will not alter the speed of its propagation. If the wave hits a barrier such as the edge of the pond, it will be reflected. A similar occurrence is observed in the reservoir when the rate of production from a well is altered. A pressure transient radiates from the wellbore at a velocity which is a function of both reservoir rock and fluid properties. As in the case of the pond, if the transient encounters an environmental alteration, it will be reflected to the well. The amplitude of the transient is not related to the radial velocity of the transient; therefore, the analysis of the transient is theoretically independent to its amplitude.