An Extension Of The Pollard Analysis Method Of Well Pressure Build-Up And Drawdown Tests

PUBLICATION RIGHTS RESERVED This paper is to be presented at the 36th Annual Fall Meeting of the Society of Petroleum Engineers of AIME in Dallas October 8–11, 1961, and is considered the property of the Society of Petroleum Engineers. Permission to publish is hereby restricted 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 JOURNAL OF PETROLEUM TECHNOLOGY or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in 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 considered for publication in one of the two SPE magazines with the paper. The Pollard method for analyzing well pressure drawdown and build-up tests presented in 1958 permits the calculation of the well skin effect and of the volume of the coarse pore volume system affected by the well. It was devised primarily to design and predict results of acid treatments. The present study extends the Pollard analysis to the calculation of the fine pore volume system (often called "matrix" porosity) and to the calculation of the "radius of influence" of a well before and after well stimulation treatment. The method permits to ascertain if a sufficient number of wells are drilled in order to drain effectively a given field or lease. The extension of the Pollard method is based on laboratory tests made with electric analogs of the various simulated porous systems. Limitations and field examples from fractured and vuggy reservoirs are given. Introduction In many reservoir engineering calculations it is important to know the pressure variations since many of the variables in reservoir engineering are dependent on pressure. It is well known that reservoir pressure in a producing or in a shut-in well varies with time, but it is not so well known how exactly the reservoir pressure varies mathematically with time. In fact, as will be discussed later, several papers have been written outlining various methods of analyses of pressure build-up curves.