What Does Annular Injection Mean?
Annular injection is one of the two ways in which cuttings reinjection (CRI) is carried out. The CRI process involves the injection of drilling waste (cuttings and slurry) into the sub-surface using high pressure pumping above the injection formation's fracture gradient.
In the annular injection method, the slurry is injected into the annular space behind the intermediate or production casing above the top of the cement. The method is a zero-discharge solution, cost-effective, weather independent, and leaves no future liability for the contractor.
The zero-discharge solution helps diminish the risks associated with the transportation, treatment, and disposal of drilling waste, especially concerning the environment.
Trenchlesspedia Explains Annular Injection
In the annular injection method of drilling waste management, the waste slurry is injected through the annular space between two casing strings into the receiving strata. The casing has to be cemented below and above the injection zone so that the drilling waste does not migrate to surrounding formations.
Annular injection injects waste into shales or other formations with low permeability. The well used for annular injection could be one that is being currently drilled or an exploratory well. Usually, annular injection is carried out in a well that has previously been drilled and completed.
The CRI process involves the milling and shearing of slurried drill cuttings and oil field wastes with water into an appropriate size. The resulting slurry is then disposed of by pumping it into dedicated disposal wells or through the open annulus of a previous well into a fracture created near the casing shoe set in a suitable formation.