What Does Compressive Stress Mean?
Compressive stress in the context of in-situ stress refers to the vertical compressive stress in a formation caused by overlying strata. Until the moment of drilling, the rock formation is in a state of equilibrium. To re-establish equilibrium, the adjacent formation will take the additional load that was carried by the removed rock.
This results in a stress concentration around the well for which support is needed and provided by the pressurized drilling fluid.
Trenchlesspedia Explains Compressive Stress
Stresses in underground formations are not uniform and change in magnitude based on direction. The stresses are generally non-homogenous, compressive, and anisotropic. Underground formations that confined and under stress fall into three principal stresses namely vertical stress (σ1), minimum horizontal stress (σ2) and maximum horizontal stress (σ3). These stresses are not uniform and vary in magnitude based on direction.
When the compressive strength of the rock exceeds in the region of maximum compressive stress around a wellbore, wellbore breakout can be induced due to that stress. In vertical wells, breakouts center at the azimuth of minimum horizontal stress, i.e. the location of maximum compressive hoop stress.