Some aspects of air-entrainment on decay rates in hydraulic pulse tests

• The role of air-entrainment in pore fluids in hydraulic pulse tests is examined.
• The increase in the viscosity and compressibility of the due to air is modelled.
• Results are given for both Voigt and Reuss bounds of the fluid compressibility.
• The error in hydraulic pulse test results due to air in the fluid is evaluated.

Important factors that can influence interpretation of the pulse tests include the compressibility and viscosity of the fluid that either saturates the pore space of the rock or is used to pressurize the chamber, which generates the pressure pulse. Fluid compressibility can be influenced by entrained air. This paper examines theoretically, the influence of compressibility and viscosity variations in both the interstitial pore water and within the pressurizing chamber, on the performance of the hydraulic pulse test. Convenient analytical results can be derived to account for variations in compressibility and viscosity resulting from entrained air. Theoretical results indicate that the entrained gas content can have an appreciable influence on the pressure decay curves, and particularly high volume fractions of the entrained air can influence the estimation of the permeability from hydraulic pulse tests. The paper concludes with a brief discussion of the influence of dissolved air on the performance of pulse tests.