Effects of pore pressure on coring-induced damage based on simulation by mesoscale stress-flow coupling numerical model

The deep in-situ environment is often characterized by high pore pressure, which will be released during traditional coring in deep rocks and lead to damage in rock samples. Hence, a novel coring technology has been proposed and systematically investigated for preserving in-situ conditions, including pore pressure, to obtain rock samples with high fidelity to the deep in-situ environment. To theoretically examine the variation in pore pressure after coring and evaluate its influence on rock samples, two kinds of mesoscopic model representing closed-pore and open-pore were established and analyzed by stress flow coupling, in which both seepage in porous matrix and flow in relatively bigger cavities are considered. An elastic-plastic-damage model associated with volumetric dilatation was introduced to reflect tensile damage. The influences of pore pressure after different kinds of coring were simulated by a series of conceptualized models, and the results revealed three kinds of situations: Pore pressure removal, pore pressure release, and pore pressure preservation. During traditional coring, the high pore pressure will neither be sealed completely nor released suddenly because the rock matrix has low permeability. The higher residual permeation pressure in the rock matrix will be caused by lower permeability, larger closed cavities or smaller open cavities. During traditional coring, the coring-induced inner damage arises nearby closed cavities. Both the damage value and the damage zone are increased with decreasing permeability. However, extra tensile damages rarely arise during in-situ pore pressure-preserved coring, which technology can also retain in-situ high pressure. Hence, the in-situ pore pressure-preserved coring technology has great significance for eliminating the distortion effect of coring to the greatest possible extent. Document Type: Original article Cited as: Zhao, L., Peng, R., Hao, P., Yang, Y., Zhou, H. Effects of pore pressure on coring-induced damage based on simulation by mesoscale stress-flow coupling numerical model. Advances in Geo-Energy Research, 2024, 14(3): 170-186. https://doi.org/10.46690/ager.2024.12.03