Multiscale evaluation of potential damage in jetted lateral boreholes

Abstract

We study the potential formation damage effects due to radial jet drilling on Bentheim sandstone, a homogeneous sandstone that is well established in terms of mechanical properties and widely used as reservoir analogue. We quantify how properties degrade with distance from a jetted hole on μm scale (porosity) and cm scale (compressive, tensile and acoustical properties). Moreover, we perform true-triaxial compression tests on samples with and without a jetted hole. It is concluded that, for this material, jetting has no direct influence on the surrounding area. No significant changes compared to intact material is found, nor can a significant change be detected with respect to distance to a jetted hole. Differences fall within the intra-block variability, and differences between blocks can be well explained by block-to-block variation. Differences in results of the true-triaxial compression tests can be attributed to a different sample geometry, which is corroborated by a numerical simulation. We conclude that the stress field around the jetted hole can therefore be well approximated by the Kirsch equations, modified for compression, and thereby accurately describe the stability of the lateral borehole.