Method of Establishing a Stabilized Back-Pressure Curve for Gas Wells Producing From Reservoirs of Extremely Low Permeability

A method of establishing stabilized back-pressure curves for gas wellsproducing from formations of extremely low permeability is presented. Actualwell performance under many different operating conditions is shown by thestabilized back-pressure curve. By use of the method, it is possible to conductback-pressure tests with a critical-flow prover on wells that stabilize slowly, and save approximately 88% of the gas ordinarily vented to obtain satisfactorytest data, with a great reduction in time required for testing. Introduction The reasons for establishing dependable back-pressure curves on gas wellshave been pointed out by previous publications. The publication most referredto, of course, is the United States Bureau of Mines Monograph 7, titled"Back-Pressure Data on Natural Gas Wells and Their Application toProduction Practices". The technique generally established therein has beenaccepted and used by many engineers; and, when proper tests are conducted, theresults can be used for the analysis and solution of several practical problemsconcerning field operation and development. Even where formations of low specific permeability are encountered, thedetermination of a well's actual performance by the back-pressure test methodpermits the engineer to analyze many problems in individual well operation andalso to predict necessary future field development. Such problems as thedetermination of the ability of a well to produce into a pipe line at apredetermined line pressure, the design of gas gathering systems and metersettings, and the determination of the time and the number of wells required tobe drilled to meet future market obligations, can be solved, in part, by theuse of a reliable back-pressure curve. In addition, the computed well deliveryrates determined by data from backpressure tests ordered by state regulatorybodies, when compared with the true back-pressure curve, permit the operator toascertain whether such data represent unstable or relatively stabilizeddelivery rates for given pressure conditions of the well. The technique of back-pressure testing, as described in this report, wasdeveloped by Phillips Petroleum Company engineers from data obtained during atesting program that started in 1944 and has been continued to date. Threehundred and eleven back-pressure tests were conducted on 299 wells located inthe southern part of the Hugoton Field. The gas-bearing zone is composed ofseveral dolomitic formations of the Permian Age; the important ones are theHerington, Upper Krider, Lower Krider, and Winfield. The average bottom-holetemperature is approximately 91'F., and the initial wellhead shut-in pressuresrange from 400 to 440 psig. The spacing pattern is 640 acres per well with eachwell located near the center of the section. The range of back-pressurepotentials on wells tested was from 500 to 23,000 Mcfd. T.P. 2545