Remedial, or secondary, squeeze cementing procedure is performed to exclude water or gas from a well, improve primary cementing job, recomplete in a new zone or repair corroded/damaged casing. Good primary cement jobs eliminate problems when drilling, completing and producing a well. If primary cement job is inadequate, and cement bond log (CBL) did not show deficiency, a great deal of money may be spent trying to repair it by squeeze cementing.
Squeeze cementing displaces cement to a desired point; it is controlled by a packer(s) or a permanent packer already in casing is used as a squeeze tool. Once at the desired depth, cement is circulated down to the squeeze point. The tool is set to isolate/protect casing from high pressure. Cement is pumped into area to be sealed off. Hydraulic pressure is applied, squeezing cement slurry against the formation. This may be done in open hole or through perforations in casing or liner. Excess cement can be reversed out of well or drilled out at a later date.
Jobs are successful if cement is left in casing opposite perforations or damaged area, and not drilled out after squeeze operation.
So plug back jobs have been the most successful. There have been poor results with block squeezes to shut off water, especially in gas wells where at common depths fractures are vertical, not horizontal, (cement layers radiating from wellbore in a circle) as was once thought.
Vertical fractures have vertical wings which make it difficult when trying to shut off water. In almost all cement squeezes, cement goes up the hole between the formation and casing. Once annular channel is shut off, producing zone can be squeezed. Whole cement does not enter formation pores, but rather the water in the cement. Water is forced into the formation under pressure, leaving cement to plate out across formation face. The water loss, coupled with a chemical reaction, sets up, or hardens, cement. If enough pressure is applied to fracture the formation, cement could enter fracture.
Important prerequisites for a good squeeze cement job are clean perforations, channels and a cement slurry designed to meet the downhole conditions and type of squeeze to be performed. Minimal blockage and clean surfaces assure a better and more thorough bond; sometimes an acid job may be used to ensure this. A wide selection of oil well cement is used for squeeze cementing, varying from heavy to light slurries. Additives adjust water/cement ratios, viscosity, set strength, pumpability time, temperature tolerance and other factors. There are many methods of applying cement under pressure.
Terms used in Squeeze cementing procedure
Bradenhead Squeeze – There is no packer in the hole. Casing valves are closed and the well is pressured up on the casing and the workstring during the operation.
Bullhead Squeeze – The packer is set when the job starts and all fluid in the workstring is pumped into the formation ahead of the cement. The casing may be pressured, if necessary, to reduce the differential pressure across the packer.
Hesitation Squeeze – Cement is pumped out through the casing perforations and into the annular area between the casing and formation. Then the pumps are stopped for a few minutes. Pumping is started and stopped until the desired pressure is obtained.