Oil well cementing is the proccess of mixing and displacing a cement slurry down the casing and up the annular space behind the pipe where it is allowed to set, thus bonding the pipe to the formation. No other operation in drilling or completion is as important in the producing life of the well as a successful primary cementing job.
The first verified use of portland cement in an oil well, to shut off water that could not be held with a casing shoe, was in 1903. After placing the cement, the operator normally waited 28 days before drilling the cement and testing. Improvements in cements, understanding WOC times, and the use of admixes have reduced WOC time to a few hours under present-day practices.
Cementing procedures are clasified in to primary and secondary phases. Primary cementing is performed immediately after the casing is run into the hole. Its objective is to get effective zonal separation and to help protect the pipe itself. Cementing also helps to
- Bond the Pipe to the formation.
- Protect producing sttrata.
- Minimize the danger of blowouts from high-pressure zones.
- Seal off lost-circulation zones or other troublesome formations as a prelude to deeeper drilling.
Secondary Cementing, or squeeze cementing, is the process of forcing a cement slurry into holes in ther casing and cavities behind the casing. These operations are usually performed for repairing or altering a completed well at some later date, or they may be used during the initial drilling process. Squezze cementing is necessary for many reasons, but probably the most important one is to segregate hydrocarbon producing zones from those formations producing other fluids. The goal on a squeeze cementing job is to place the cement at the desired point or points necessary to accomplish the purpose.
- Squezze cementing is also employed to:
- Supplement or repair a faulty primary cementing job.
- Reduce the gas-oil, water-oil, water-gas ratio.
- Repair defective casing or improperly placed perforations.
- Minimize the danger of lost circulation in an open hole while drilling deeper.
- Abandon permanently a nonproductive or depleted zone.
- Isolate a zone prior to perforating for production or prior to fracturing.