A frac-out occurs when drilling fluid penetrates fractured bedrock, or seeps or flows into the rock and sand that surrounds the bedrock and travels toward the Earth's surface. A frac out frequently occurs as the result of excessive down-hole pressure caused by a poor choice of drilling fluids or poor drilling practices.
Trenchlesspedia Explains Frac-Out
A frac-out has the potential to damage the surface that overlays the horizontal bore, or to become an environmental problem that the trenchless contractor must deal with. When drilliing fluid pressure in the borehole is excessive, it can fracture the surrounding or adjacent bedrock.
When that bedrock fractures, the fluid will travel along the path of least resistance to alleviate the pressure within the bore. Almost always, that path leads to the surface of the area above the trenchless work area. This means the contractor will have to provide additional, unpaid work at the site related to environmental cleanup.
The cleanup will vary from state to state — depending on the extent of the frac-out. State requirements are, at times, more stringent than federal requirements. A contingency plan addressing the possibility of a frac-out during a drilling operation is one potential measure to reduce potential costs.