An improved straight-line method for permeability and porosity determination for tight reservoirs using pulse-decay measurements

Accurate assessment of the formation rock permeability and porosity is crucial for geotechnical applications. For tight formation rocks, separate measurements of permeability and porosity result in high time costs and degraded accuracy. This contribution presents an improved straight-line method that allows simultaneous permeability and porosity determination in a single pulse-decay measurement. In the proposed method, the permeability is determined by the slope of the unilateral pressure changes in the semi-log plot versus time, and the porosity is obtained through the law of mass conservation. For the first time, three analytical expressions are derived that can give the value of the dimensionless equilibrium pressure without the need to reach the final equilibrium. These expressions also provide a practical way to determine the onset of the late-time stage, which helps to reduce the errors caused by mistaking the early-time data for the late-time one. The proposed method is applicable to both the two-chamber and the one-chamber pulse-decay measurements. The accuracy and prac-ticability of the present method have been demonstrated through experimental measurements and literature data.

Automated summary

This contribution presents an improved straight-line method that allows simultaneous determination of permeability and porosity in a single pulse-decay measurement. Analytical expressions are derived to give the value of the dimensionless equilibrium pressure, reducing errors caused by mistaking early-time data for late-time one.