Permanently isolating one or more producing zones from another is occasionally required as a means of maximising net flow from a producing well. In this case, zonal isolation is required to minimise the crossflow of a high-temperature depleted, perforated, upper sand section from a lower, higher-pressured zone targeted for future production. Any chemical isolation treatment applied to the upper sand perforations must withstand not only the high temperature involved, but also differential pressures in the region of 300 bar (4,351 psi). Following the treatment, flow would then be initiated from the lower sands by removing an isolating sand plug. By effectively plugging a formation, crossflow between the two producing sections of the well would be minimised, the degree of which would be dependent upon the efficiency of any final perforation seal.
The treatment incorporates specially sized and selected particles designed to invade the matrix permeability, a temperature-triggered bonding agent and ingredients which ensure that the treatment reaches the target. The mixture of the bonding agent and the sized particles creates a well defined seal within the perforation tunnel.
Both the development and testing of the perforation plugging treatment incorporated high-temperature, high-pressure permeability plugging tests in combination with innovative coreflood testing techniques. Detailed analysis of the treatment, cores and perforations with electron microscopy and computed tomography (CT) allowed the initial idea to be tailored and perfected for the specifics of the field application.
This paper will discuss the laboratory development of a perforation plugging treatment designed to limit reservoir crossflow under conditions of high-temperature and high-differential pressures.