When a certain section length of an oil or gas well has been drilled successfully, the drilling fluid cannot prevent the wellbore permanently from collapsing. Therefore, metal tubes - casings - are introduced and fixed with cement to stabilize the well.
The first step of oil well cementing is pumping the cement slurry downhole through the inner side of the casing. Then the slurry is squeezed upwards in the annulus between casing and formation wall, filling all void spaces.
This cement layer separates different subterranean formations from each other. This zonal isolation is necessary in order to prevent exchange of gas or fluids among different geological formations. Subsequently, the drilling process is continued with a smaller diameter.
Sprint Oil & Gas Services provides both primary and remedial cementing services and products.
Primary and remedial cementing services.
Primary cementing is the process of placing cement slurries in the annular space between the casing and the borehole or previous casing or both. Slurry is pumped down the string to be cemented, exits the bottom through the shoe and, with a preflush normally pumped ahead of it, and displaces the mud while moving up the annulus. Cemented strings include conductor pipe, surface casing, intermediate casing, production casing and liners. The downhole equipment associated with cement placement for each casing/pipe type is the main difference in the cementing techniques:
- stage cementing where the cement column is placed in the annulus in "stages" using a stage collar, because a downhole formation is unable to support the hydrostatic pressure exerted by a long column of cement
- stab-in cementing where the slurry is pumped down drillpipe to the casing bottom using stab-in equipment liner cementing where the slurry reaches the shoe by traveling first through drillpipe, next through the liner hanger and then through the liner itself; final cement placement is across the liner interval only (with some cement left immediately above the liner).
The objectives of a primary cement job vary depending on the application. They can be any combination of the following.
- prevent the migration of formation fluids or gases in the wellbore annulus (zonal isolation)
- anchor and support the casing string
- protect the casing string against corrosion
- confine stimulation treatments to target intervals (zonal isolation)
- meet government regulations
- provide customer value cost effectively.
These objectives are met when the cement job achieves:
- effective mud removal, which results in a complete cement sheath in the annulus
- a hydraulic seal, which provides zonal isolation
- the top of cement (TOC) as per design.
Remedial Cementing is the process of placing specially formulated cement slurries to cure losses or bad primary cementing, either by pumping through casing, drill pipe, or coiled tubing.