8.1 Introduction

Type curve matching provides methods2 ^,6 ^,8 for analyzing transient gas well tests with known dimensionless pressure P _D and time t _D. Type curve matching techniques may be used for drawdown, buildup, interference, and constant pressure testing. For single well testing, type curve matching should be used only when conventional analysis techniques such as those illustrated in Chapter 5 cannot be used. In such cases, type curve analysis can provide approximate results. This chapter discusses the quantitative use and applications of type curves in gas well test analysis. The most generally useful type curves have been selected and are included herein. Fundamentals of type curve use are presented and will allow the reader to understand and to apply newer type curves as they appear in the literature.

8.2 Fundamentals of Type Curve Matching

A log-log plot of the line-source solution the Theis solution shown in Figure 8 1 may be used to analyze such tests. Plots such as the one shown in Figure 8 1 are known as type curves. The basis for the type curve approach can be understood if we consider the definition of P _D( r _D , t _D) and . Taking logarithms of these definitions, we obtain

and

Figure 8 1: Line source solution.

The first terms on the right-hand sides of Eqs. 8 1 and 8 2 contain the characteristic constants that govern the pressure distribution in the reservoir. Inspection of Eqs. 8 1 and 8 2 suggests that a plot of the logarithm...