Foam Cementing Design and Application: A Cure for Low Gradient-Associated Problems in Deepwater Operations in the Gulf of Guinea

Abstract

Abstract Cementing in the deepwater environment could pose some challenges because deepwater formations are buried with much reduced overburden. This gives a lower fracture gradient resistance than the same formation at the same sedimentary depth onshore. In situations like this, the relative density-to-compressive strength ratio of the cement slurry used for zonal isolation becomes critical; hence foamed cement helps to address these challenges. Slurries ranging in density from 4 to 15 lb/gal can be prepared with foamed cement. Foamed cement can be used at temperatures from 28 to 600ºF (82 to 1112ºC). In this project, Laboratory analysis of foamed and unfoamed cement at different slurry weights was determined and compressive strength results were evaluated. Test results indicated that the compressive strength for 12.0 ppg unfoamed cement after 24 hours was 254psi while the foamed slurry of 11.8 ppg gave compressive strength of 1050 psi after 24hours. It is imperative to note that conventional slurries at higher slurry weight that will give higher compressive strengths will fracture weak formations and not recommended. Foamed cement slurry offers a comparative advantage of enhanced mud removal, good ductility, fluid loss and gas migration control, insulation properties and excellent compressive strength development at low slurry density. However, the disadvantage of foamed cement is the need for specialized cementing equipment for both field application and laboratory testing, nevertheless, the associated benefits arising from application of foam cement in deep water weak formation environments makes it a slurry of choice in locations such as Gulf of Guinea.