No abstract

Channeling behind casing connecting two sandstone reservoirs in well 13 was suspected due to poor cement job, possibly due to the high angle well of 76 deg. Avoiding communication behind casing between two sands is detrimental for field reservoir management where reservoir pressure maintenance with water injector wells is paramount for continuous production. This paper describes the treatment background, engineering approach, laboratory testing and QA/QC procedures, fluid design stage and job execution using the propriety low viscosity polymer system to seal off channeling behind casing. Cement bond log performed in well 13, a 76 deg. directional well drilled offshore Peninsular Malaysia showed very poor bond behind casing. An injectivity test conducted by setting a retrievable packer in between perforation intervals of the two sand bodies near the suspected channeling confirmed communication between the two sands. Repair alternatives were evaluated opting between cement or polymer gel squeeze. Hydraulic calculation based on the injectivity test result, roughly set the equivalent channel diameter as 0.15 in. Cement squeeze was therefore rejected in view of the small and long cement channel of 109 m. An alternative method to squeeze a low viscosity polymer system into the channel behind casing was hence designed for the purpose of sealing off the channel. The procedure developed was to create a single perforation in between the two perforations in both reservoirs and squeezing the polymer. A retrievable bridge plug and a retrievable packer straddled the squeeze perforation interval and a polymer gel squeezed through the said perforation. After several squeezes each followed by a curing time, pressure tight seal isolating the two reservoir sands was obtained. This was confirmed by setting a retrievable packer above the lower most perforation in the reservoir sand followed by injecting brine while monitoring for returns through the upper perforation, which were none. This unique method, never applied before, to repair a 109 m continuous cement channel between two reservoir sands separated by a thick shale layer using cross linked gel was successful. Two years later the seal is still intact with production from this dual completion well continuing trouble free. The proprietary gel applied is a cross linked low viscosity polymer which cures under downhole temperature to form a tough seal. It is learned that running a retrievable bridge plug and a retrievable packer in tandem in high angle well best not be attempted in future, instead, both should be run separately. Acidizing through the squeeze perforation will assist to improve squeeze pressure. Application of cross linked gel to repair cement channel has been proven to be a viable alternative to cement squeeze.