Combined Analysis of Postfracturing Performance and Pressure Buildup Data for Evaluating an MHF Gas Well

Abstract

This paper presents a method of combining postfracturing performance datawith postfracturing buildup data for analysis on the same constant-ratetype curve. This combination of buildup and production data isaccomplished through the use of the superposition principle. The method allows the use of production data that contain occasional shut-in periods of long duration. Introduction Low-permeability (less than 0.1 md) gas wells mustbe stimulated with massive hydraulic fracture (MHF)treatments to be commercial. Once a well has beenstimulated, it is important to determine the lengthand conductivity of the resulting fracture asaccurately as possible to predict rates and reserves andevaluate the effectiveness of the stimulation. Two types of data normally are available toperform the required analysis. The first type isroutinely collected data such as gas flow rates and flowing wellhead pressures. The second type of datais that from specially designed tests such as pressurebuildup tests. There are various methods availablefor analyzing both kinds of data, but all of themethods have certain limitations. Current analysis techniques are satisfactory forfinite-flow-capacity fractures when formation flowcapacity kh is known and sufficient production datawithout shut-in periods is available to perform atype-curve match as shown by Cinco et al. andAgarwal et al. However, one disadvantage of MHFtreatments is that they often cause the stimulatedwells to produce large volumes of load water(returning fracture fluids) for several weeks ormonths. Production data obtained during thiscleanup period usually are not applicable fortype-curve matching purposes with the currently available type curves. Since type curves normally are plottedon a log-log scale and exhibit the most character atsmall dimensionless times, the loss of the early-timeproduction data disproportionately reduces thelength of the available data band and is critical to theproblem of obtaining a satisfactory match. The purpose of this paper is to present a method ofcombining the production and buildup test data sothat their concurrent analysis overcomes some of thelimitations of either individual data set. Thesuperposition principle is used in this combination, and the analysis of the resulting data set shouldprovide a more accurate result than previouslypossible. This combination has the potential togenerate field data curves of sufficient length that theshape of the data curve may be sufficiently definitive to determine formation flow capacity by type-curveanalysis. Additionally, this method makes it possibleto use production data that contain occasional shut-in periods of long duration. JPT P. 1711＾