Click To Find Out Why Your Borehole Needs Compressing
Reasons For Boreholes Compressing - water quality
Borehole instability is the undesirable condition of an open-hole interval that does not maintain its gauge size and shape and/or its structural integrity. Losing the drilling borehole integrity is a trenchless construction hazard that can lead to borehole collapse.
In general, groundwater contains no or low levels of harmful pathogens but it can be polluted with naturally occurring chemicals. Unfortunately, the quality of water drawn from hand-pumps fitted to boreholes is variable. Contamination can be caused by poor sanitary protection at the top of the borehole. The installation of a sanitary seal and a well apron can dramatically reduce contamination from the ground surface
Depending on the drilling borehole function, hole fragility causes damage to equipment or potential injury to employees.
You need to know the signs of a hole that is losing structural stability and the different ways the structure can be destabilized.
The causes of Borehole Instability can be grouped into the following classifications:
· Mechanical failure caused by in-situ stresses
· Erosion caused by fluid circulation
· Chemical caused by interaction of borehole fluid with the formation
Types of Hole Instability and Its Associated Problems
There are several types of borehole instability, each with a unique cause. Understanding the different types can allow workers to ensure proper preventative measures are in place.
· Hole closure or narrowing
· Hole enlargement or washouts
Borehole closure is a narrowing time-dependent process of borehole instability. When a borehole begins to narrow or close, workers refer to it like a creep under the overburden pressure. Hole closure causes increased pipe sticking, increased difficulty of casings landings and increased torque and drag before total loss of the borehole.
The following problems are associated with hole closure:
· Increase in torque and drag
· Increase in potential pipe sticking
· Increase in the difficulty of casings landing
Hole enlargements are commonly called washouts because the hole becomes undesirably larger than intended. Hole enlargements are generally caused by:
· Mechanical abrasion caused by drill-string
· Hydraulic erosion
· Inherently sloughing shale
Problems associated with hole enlargement includes:
· Increase in hydraulic requirements for effective Hole Cleaning
· Increase in potential hole deviation
· Increase in cementing difficulty
· Increase in potential problems during logging operations
Fracturing occurs when the wellbore drilling-fluid pressure exceeds the formation-fracture pressure. Lost Circulation and possible Kick occurrence are the associated problems.
Borehole collapse occurs when the drilling-fluid pressure is too low to maintain the structural integrity of the drilled hole. The associated problems are pipe sticking and possible loss of well.
Methods of Preventing Borehole Collapse
Constant monitoring of borehole integrity is essential to preventing integrity loss. Workers monitoring the situation can adjust trajectory, mud weight and hole stability.