Squeeze Cementing Job Failures
Improper Slurry Selection
The cement slurry must be designed so that the filtrate enters the formation and the cement filter cake builds up in the perforation tunnels in the required amount of time. The key slurry parameters of fluid loss and viscosity must be carefully selected.
If fluid loss is uncontrolled, cement may dehydrate and bridge off the upper portion of a perforated interval before slurry is displaced to the lower perforations. Conversely, very low fluid loss can result in very slow filter-cake development and unacceptably long placement operations. Slurry-fluid (filtrate) loss can be controlled with additives as required over the wide range of temperature and pressure conditions normally encountered.
Excessive squeeze pressure
In a low pressure squeeze job, it is important that the squeeze pressure never exceeds the fracturing pressure of the formation. It is important for all personnel to be aware of the downhole impact of increasing pump pressure to “finish the job.”
Plugged perforations
Not all of the perforations in an interval are open and receptive to pumped fluids or cement before squeezing. A partially plugged perforation tunnel can behave as if it is properly cemented when pressure is applied during a squeeze, and then clean up easily when exposed to a pressure differential in the opposite direction. In the case of previously producing perforations, those at the top of the interval are often the only ones completely open to flow. Perforation washing is the only way to increase the chances of all perforation being equally receptive to the squeeze.
Improper packer location
If the packer is set too high above the perforations, the cement slurry can become contaminated as it channels through the mud or completion fluid in the casing. If it is set too close to the perforations, pressure communication through the annulus above the packer may cause casing collapse. The length of the tailpipe extension below the packer, and the position of the tailpipe shoe relative to the perforations, can be adjusted to accommodate specific situations.
