Improved Zonal Isolation Through the Use of Sealants Before Primary Cementing Operations

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435.References at the end of the paper. AbstractZonal isolation in injection, geothermal, and producing wells is critical both to reservoir evaluation efforts and to operations, but often, cementing between the casing and the wellbore is still the only method of zonal isolation performed in many wells. Although zonal isolation and well diagnostics techniques have improved, primary cementing techniques may be inadequate for some reservoir conditions, resulting in undesirable water flows, gas flows, or both. If zonal isolation is inadequate, then expensive, often complicated remedial cementing work will be needed for improved well and reservoir performance.If conformance technology is applied during the drilling phase, it can improve the performance of primary cementing processes, making them safe and economical. Conformance treatments seal problem intervals before primary cementing, thereby alleviating potential well-control problems. These treatments also help ensure successful primary cementing operations and prevent isolation loss caused by the casing expanding and contracting during production-pressure cycles. The formation itself, rather that the cement sheath alone, becomes the zonal isolation mechanism.During the drilling phase, zonal isolation requires the use of coiled tubing, a hydrajetting device, a depth-correlation device, and a sealant. The sealant should be water-thin during placement, and should become an elastic polymer only after it is set in place. This zonal isolation technique requires an understanding of (1) depth correlation to openhole logs, through the use of mud-pulse technology, and (2) hydrajetting tech-niques that remove mud filter cake while placing the sealant. This paper presents examples of this technique for a 7 7 /8-in. wellbore and a 13 ½-in. wellbore.