By quantitative interpretation, we mean estimation of various reservoir parameters using accepted calculations. These methods are derived from the work of a number of authors, all of which use a simplified solution of the diffusivity equation.
In its most simplest terms, this equation states that fluid flow in a porous medium is in proportion to the pressure drop induced, the properties of the fluid and the properties of the porous medium (rock). Many authors have provided specific solutions to this equation to suit various needs. From the DST point of view the most appropriate solution has been provided by Horner.
The Horner solution to this equation assumes the following. Constant, laminar, radial flow, of a fluid, of small or no compressibility from a reservoir of infinite extent, homogeneous porosity and permeability into a vertical well of small radius. Since gas does not satisfy the assumption requiring small or no compressibility, a special case has been developed taking into account the ideal gas law.
From these solutions, gas analysis and fluid analysis equations can be used to estimate various reservoir parameters from analysis of the buildup data, provided you can construct a Horner plot and derive the static reservoir pressure and Horner slope. For more on this, see Reservoir Pressure and Horner Plots.