Definition - What does Wellbore Stability mean?
Wellbore stability refers to the structural integrity of a wellbore that prevents it from collapsing. Mud loss is frequently encountered while drilling and happens when the mud weight essential to maintain wellbore stability and well control exceeds the fracture resistance of the formation, especially in depleted reservoirs.
Underground formations are subjected to stresses such as vertical stress, minimum horizontal stress, and maximum horizontal stress because of their confined nature.
Maximum horizontal stress (sH) is an important parameter for modeling wellbore stability and drilling optimization.
Trenchlesspedia explains Wellbore Stability
Maintaining wellbore stability is very important during drilling operations. To prevent an unstable wellbore, the shape and direction of the wellbore must be controlled while drilling. A proper balance needs to exist between controllable and uncontrollable factors in a drilling operation.
Unpredictable factors include earth stresses, pore pressure, and rock strength; controllable factors include wellbore fluid pressure and chemical composition of the mud.
Some of the causes of an unstable borehole are:
- Removal of confinement condition.
- Creating a field of stress concentration around the wellbore.
- Creation of free surface allowing displacement.
The wellbore has to be stabilized with mud weight to prevent the hole from collapsing.