Novel Approach to Repairing Cement Channeling Between Two Reservoir Sand Bodies with Differential Pressure Gradient

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.

Preparation and Characteristics of a pH Intelligent Response Blocking Agent for the Microcrack in the Cement Sheath

“…Consequently, cement extrusion operations are primarily effective for larger crack channels, while smaller cracks are often left untreated, leading to a low success rate for cement extrusion in controlling annular water channeling. 21 To successfully control water channeling in the annulus, researchers have proposed a method that uses underground gelling profile control and water-blocking agents as sealing fluids to seal microcracks in the annulus cement sheath. This sealing fluid is a polymer aqueous solution before gelling and does not contain solid particles, making it suitable for use as the annulus sealing fluid.…”

“…Unfortunately, the solid particles present in the cement slurry, such as cement or ultrafine cement, are often too large to enter crack channels that are smaller than 120 μm. Consequently, cement extrusion operations are primarily effective for larger crack channels, while smaller cracks are often left untreated, leading to a low success rate for cement extrusion in controlling annular water channeling …”

Bentonite–Acrylamide Hydrogels Prepared by the Nonmixing Method: Characterization and Properties

“…The field applications indicate that the effective period of hydrogel sealing annular channeling is at least 2 years. 13,14…”

“…The field applications indicate that the effective period of hydrogel sealing annular channeling is at least 2 years. 13,14 This paper proposes a novel application of hydrogels in improving the sealing of cement sheath in oil and gas wells. The process of oil and gas well cementing operation is to insert a casing into the oil and gas well after drilling the oil and gas well hole and filling the cement slurry between the casing and the well wall.…”

“…In the production process of oil and gas wells, after an interlayer cross flow is formed in the annulus by the crack of the annulus cement ring, the hydrogel is squeezed into the channel to prevent the fluid flow from high-pressure formation to low-pressure formation through the channel. The field applications indicate that the effective period of hydrogel sealing annular channeling is at least 2 years. , …”