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.
Numerous methods have been applied in matrix acidizing over the previous decades to successfully stimulate multiple zones. These methods have also been implemented in fracture acidizing with varying degrees of success. This paper discusses the application of a new biodegradable material used for diversion in multiple zones or long formation intervals and presents improved results obtained using a new biodegradable diverter. Acid-fracturing diversion can be more challenging than diversion for matrix acidizing. To effectively stimulate multiple or large zones, the diversion treatment should be able to bridge not only the perforations themselves, but often inside the fracture system as well. This can be difficult because acid reacts with the rock, forming an etched/enlarged path, thus the diversion also requires bridging inside this conductive path. This differs from matrix acidizing techniques, in which the diversion depends mostly on the perforations in an interval(s) and the stimulated reservoir permeability. Historically, several methods have been implemented for acid-fracturing diversion, such as ball sealers, viscous fluids, packers, etc., resulting in limited success or cost-ineffective results. The new biodegradable material helps improve acid fracturing diversion success in multiple zones or long formation intervals. The development of this biodegradable material is discussed along with a case study. Also, details are provided of the biodegradable material evaluation that consists of 1) pre and post-temperature logs, 2) pre and post-injection logging profiles, 3) pre and post-production history, and 4) further recommendations. The results of the evaluation methods show that the biodegradable material can be used as an effective alternative diversion method to seal existing perforations and effectively stimulate all perforated intervals. Production increased more than threefold, and the targeted fracture height was achieved based on the temperature log data.
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