**5. Well test analysis**

 Well test analysis—also known as pressure transient test analysis—consists of methods of finding and evaluating information regarding the well and reservoir. More specifically, it involves the manipulation and measurement of flow rates and pressures which can then be linked to well and reservoir conditions. The process primarily entails altering the well flow while monitoring temporal variations in pressure [37] or vice versa [38]. The magnitude and changes in pressure are used to deduce the reservoir size, wellbore damage, boundaries and heterogeneities (e.g. fault positions), reservoir pressure at the drainage region, well deliverability, flow rate [37] and other reservoirs or related parameters such as hydraulic connectivity, skin effect and permeability.

 Well test analysis is the process of assessment and interpretation of data obtained from well tests using a variety of techniques. A diagnostic set of plots consisting of trends of pressure and its derivative (relating to time) against time is a common tool that facilitates the interpretation of well tests (pressure transient tests) [37]. The trend of pressure on these plots can then be used to determine the flow regime. For instance, flow regime *specialised* plots (∆*P vs f*(∆*t*)) aid the identification of flow regimes [39] (e.g. radial, linear, bilinear and spherical flows), where ∆*P* is the change in pressure and *f*(∆*t*) is a flow regime-specific function which is dependent on changes in time. An alternative approach (the Homer method) introduced by Homer [40] to overcome certain shortcomings of *specialised* plots measures ∆*P* against a superposition time specific to a given flow regime.

Over the years, the manner of conducting well test analysis has evolved. Types of well test analysis methods (interpretation methods) include straight line, pressure type curve and pressure derivative analysis and deconvolution; these are listed in order of the period they were developed. Detailed description of these methods is given in Gringarten [39].
