Pressure Buildup Analysis of Fractured Wells Producing at High Flow Rates

Abstract

Summary The use of type-curve matching in pressure-transientanalysis has become an essential method for estimatingreservoir parameters with short-time data. Although theoriginal type-curve matching techniques were based onsolutions for pressure drawdown problems, thesesolutions have been extended, and justifiably so, to pressurebuildup problems. However, there has been anindiscriminate use of these solutions interchangeablywithout proper justification for each application. As thispaper points out, the drawdown solution is not the same paper points out, the drawdown solution is not the same as the buildup solution for a fractured well producing athigh flow rates before shut-in. The bilinear period, however, is observed in the buildup solution. In this paper the effects of producing time on pressurebuildup analysis also are investigated for fractured wellsat low and high flow rates. An example is presented foranalyzing short-time data for a fractured well producingat high flow rates. Introduction Pressure buildup testing is probably the best known and Pressure buildup testing is probably the best known and most extensively used of all transient well-testingtechniques. During a pressure buildup test, a producing wellis shut in, and the pressure/time performance of the wellis recorded and analyzed for reservoir properties andwellbore conditions. The latter are analyzed on the basisof the early-time period of the test. In general, pressure buildup analysis can becomplicated by many factors such as producing time andwellbore and boundary conditions. Recently, Agarwalpresented a study showing that the effects of producing presented a study showing that the effects of producing time on pressure buildup analysis can be eliminatedcompletely, by replacing the dimensionless shut-in time by anequivalent dimensionless term, teD. Such a procedurenormalizes the effects of producing times, and henceconventional drawdown type curves can he used. Raghavan made a similar attempt to account forproducing time effects by presenting new type curves for producing time effects by presenting new type curves for dimensionless pressure rise vs. dimensionless shut-intime, with producing time as a parameter. We havefound this concept a useful one and have incorporatedthe dimensionless pressure rise concept with theAgarwal method and have included them in this study. Analyzing early-time pressure buildup data forfractured wells is similar to techniques used for drawdowndata. The use of type-curve matching has improved thequality of this early-time analysis greatly. One of thefirst papers to introduce type-curve matching forfractured wells was by Gringarten et al. Their studypresented new values of dimensionless pressure drop vs. presented new values of dimensionless pressure drop vs. dimensionless time for a fracture in an infinite reservoir.Several cases were studied involvinginfinite-conductivity vertical fractures, uniform-flux verticalfractures, and horizontal fractures. In 1976, Cinco-Ley et al. used a semianalyticalmethod to simulate the transient-pressure behavior of awell with a finite-conductivity vertical fracture in aninfinite slab reservoir. Type curves as well assemilogarithmic analysis methods were presented foranalyzing the short-time data. Agarwal et al. presentedsimilar results for the constant-rate case and introducedtype curves for the constant-pressure case. This analysiswas designed mainly for massive hydraulically fracturedwells. JPT P. 2656