Distinguished Transient Testing

Abstract

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Introduction Pressure transient testing involves perturbing one or morewells and observing the result perturbing one or more wells and observing theresult (either pressure or flow rates) at the perturbed well and/or adjacentwells. The result of a field test is matched with mathematical models ofincreasing complexity until a reasonable agreement results. The objectives aremathematical model dimensions and characteristics. These are assumed typical ofaverage characteristics of the real system. This field of study began in theearly 1930's in several parallel technologies both within and peripheral topetroleum engineering. Examples include formation evaluation through drillstemtesting, pump testing of water wells, and performance testing of oil wells. Amature body of literature exists today. The purpose of this paper is to reviewsignificant findings in this field and to identify some remaining problems. Classic Studies The purposes of pressure transient analysis include:(1)determination of the condition of the well-i.e., whether the sandface at thewellbore is damaged or has been stimulated,(2)the quantitative value of thepermeability in the drainage volume of the well,(3)the mean formationdrainage volume pressure, and(4)quantitative information concerning pressure, and(4)quantitative information concerning the shape and size of the drainagevolume and its porosity. porosity. Obviously, there are other objectives.Quantitative information on the preceding four items would answer suchquestions as whether the low productivity of a given well is caused by pluggingof the well, by low formation permeability, or by a low driving force and/orformation conductivity available for moving fluid into the well. Thisinformation would provide a sound basis for decisions involving costlystimulation of a well or other operating procedures. In the petroleumliterature alone. more than 400 technical papers have been published on thesubject of pressure transient analysis in the past 50 years. A pressuretransient analysis in the past 50 years. A similar number of publications existon pump test analysis in the field of groundwater hydrology. This literaturehas developed because the pressure behavior of a well can be measured easilyand is a useful quantity. Instruments for measuring maximum pressures in oilwells were developed and used in the pressures in oil wells were developed andused in the U.S. during the early 1920's. These devices included bourdon tubegauges that recorded by stylus mark on a blackened metal sheet and floats orsonic echoes to measure liquid levels in wells. By 1931 continuously recordinginstruments such as the Amerada, Humble, and MacDonald gauges wereavailable. One of the early applications for bottomhole pressures (BHP's) in wells wasa measurement of the pressures (BHP's) in wells was a measurement of the staticformation pressure. After a well had been shut in for a period of time, such as24 to 72 hours, a BHP measurement was made as an indication of the staticformation pressure. This procedure worked for permeable, high-productivityreservoirs. Engineers permeable, high-productivity reservoirs. Engineers soonrecognized that static pressure measurements depended on the shut-in time. Thelower the permeability, the longer the time required for the permeability, thelonger the time required for the pressure to equalize. This led to theimportant pressure to equalize. This led to the important realization that whena well was shut in, the duration of the pressure buildup was a reflection ofrock permeability pressure buildup was a reflection of rock permeability aroundthat well. It appears that one of the first determinations of formationpermeability from pressure transient data was published by Moore et al. in1933. An interest in transient phenomena and the mathematical description oftransient phenomena appears in many fields and literatures in the early 1900's.This paper focuses mainly on the western petroleum engineering literature. Theliterature is cited petroleum engineering literature. The literature is citedto show development of ideas rather than to present a scholarly listing ofreferences. A classic study of pressure transient analysis involving pumptesting of water wells was published by Theis in 1931 this paper was reportedin 1980. Among other things. Theis discussed analysis of pressure recoverydata, referred to as pressure buildup pressure recovery data, referred to aspressure buildup data in petroleum engineering. These data consist ofinformation obtained after a well is produced at a constant rate for a periodof time and then is shut in and pressures are allowed to equalize. Theissuggested a pressures are allowed to equalize. Theis suggested a form ofgraphing and analysis that remains one of the basic techniques employed inpetroleum engineering to this day. The method was published later by Homer. TheTheis pressure recovery graph of groundwater hydrology is known in petroleumengineering as the Homer pressure buildup graph. p. 1407