The Changes to the Rock Physical and Mechanical Properties Near the Hole Produced by Successive Impacts of a Steel-Particle Water Jet: A Case Study in a Tight Sandstone

Particle impact drilling (PID) is a promising technology to enhance the rate of penetration in hard and abrasive formations. The changes to physical and mechanical properties near the crater of a full-size tight sandstone sample after successive impacts of a steel-particle water jet are investigated by different scales of rock physics measurements to estimate the range of the damage zone. Similar measurements are also carried out on a sample from the same formation without steel-particle water jet as a reference. The results indicate that: (i) there is a damage zone around the crater with induced cracks and pore collapse caused by the impact stress wave produced by the steel-particle water jet. The dimensionless depth of the damage zone from the crater’s surface is about 0.69 times the jet diameter (d₀). Within the damage zone, the dense compaction zone is just near the crater surface within a dimensionless distance of about (0.02–0.06) d₀, where the porosity and the permeability slightly decrease, and show significant strength decrease. (ii) The changes of the porosity and the P- and S-wave velocities after steel-particle water jet at core scale are neglectable. Compared to the reference sample, the permeability at the lateral of the crater is (4.52–30.90) times higher, while the permeability beneath the bottom of the crater is 79% lower. The uniaxial compressional strength (UCS) decreases by 15.6%–65.7%. (iii) The indentation hardness after particle jetting shows a significant decrease. The macro-indentation hardness decreases from 1.92 GPa to 1.30 GPa at core scale. Within the damage zone, the hardness and the Young’s modulus calculated from nanoindentation tests decrease with the increase of the distance to the crater’s surface. This work as a case study provides new experimental evidence of the evolution of rock damage by the impact stress of the steel-particle water jet.