Laboratory Validation of Microannulus Repair Using Nanosealant Technology: Pre- and Posttreatment Logging and Permeability Characterization

Abstract

With aging oil and gas fields, permanent plug-and-abandonment activity is becoming significant and requires solutions capable of repairing leak paths. The use of nanosealant technology to treat defects in annular cement was evaluated using ultrasonic logging and permeability tests on test cells. A repeatable testing procedure was developed to validate the usability of the nanosealants to repair cemented annular barriers. Two identically constructed test cells were fabricated with 7-in. and 9 5/8-in. casings filled with standard Class G cement. Pressurization of the inner casing during cementing enabled a controlled debonding of the annulus cement and the 7-in. casing upon relieving the pressure after the cement was cured. Permeability tests with water and ultrasonic logging measured the baseline state for the test cells in dry and wet conditions before treatment with a nanosealant solution. After treatment, permeability testing and ultrasonic logging in dry and wet conditions were repeated, and the results were compared with the baseline measurements. The test cells were shown to have equivalent properties with respect to permeability and debonding and demonstrated along with related experiments that a consistent and repeatable procedure for the qualification of microannulus treatment materials can be followed. The nanosealant was able to penetrate a microannulus with an initial hydraulic aperture of about 50 μm, and the permeability measurements showed that the permeabilities were significantly reduced in both cells after the treatment. Ultrasonic logging using pulse-echo and flexural measurements results indicated improvement in the bond quality. Even though nanosealant has been used successfully in the field, this work represents the first comprehensive laboratory validation of the product supported by logging measurement and provides insight into the nano-sealant activation mechanism. A procedure for consistent fabrication of test cells for qualification of microannulus treatment materials was demonstrated. A multidisciplinary team developed a methodology that combined physical flow measurements with ultrasonic measurements to validate the performance of a nano-sealant system and confirm the coverage of the microannulus.