A New Cost Effective and Reliable Water Shutoff System: Case Study in Kuwait

Abstract

Abstract Increased water cut represents one of the biggest challenges to the oil industry, with more than 75% of the produced fluid being water that brings an increased cost per barrel of oil through water handling, scale deposition, corrosion, and mainly the bypassed oil reserve. Water shut off solutions range from mechanical solutions like bridge plugs to chemical treatments that include cement, resins and polymer gels. Cement applied as a plug or a squeeze treatment is often the preferred option to the operating company for isolating unwanted production intervals near the wellbore, and crosslinked polymer systems are also commonly used when deeper penetration is required. However, the success of these treatments often suffers from mixed fluid quality, zonal isolation (cementing quality), proper placement, numerous downhole conditions and more importantly backflow of unset cement slurry or immature gels while cleaning up leftover slurries in the wellbore or pulling out the work string after the treatment. In this paper, a new system based on a single nano-additive is described to shut off a water zone in a South Kuwait regional oil producer. The new system, which does not require curing but acts rapidly in porous media, addresses the concern of backflow associated with unset cement or crosslinked polymer fluids. The objective of this treatment was to seal off the upper zone that produces mostly water, reduce overall water cut from 90% to less than 10%, and test the productivity of the lower zone. The well configuration does not allow zonal isolation without a rig, so cement and other known chemical treatments were unsuitable for this application. Eighteen barrels of the water shut-off treatment was pumped through coiled tubing (CT) and injected into a 34 ft zone resulting in nearly immediate response through increased wellhead pressure. The injection was resumed every three to four hours to ensure a complete sealing of the target interval. The fluid starts workingupon injection into porous media but always remains as liquid phase when kept in the wellbore or surface tanks, so there is no concern about sticking or plugging the coil. The operational time was reduced compared to normal water shut off jobs, and the single additive fluid is low viscosity making surface mixing simple. The novelty of this water shut-off system is efficient sealing of a high permeability formation with minimal fluid and achieving a drastic water cut from 90% to1%. This new system, unlike polymer-based systems, doesn't degrade with temperature, water hardness or salinity, and plugging of the porous media works by acompletely different mechanism leading to a more robust barrier against water production with reduced interventional risk.