Innovative Approach to Enhanced Well Integrity Evaluation in Unconventional Completions with Fiberglass Casings

Abstract

More wells are being completed with fiberglass casings to overcome the challenge of corrosion of the carbon steel casings. Fiberglass casing is expected to increase the longevity of the wells. The wells completed with fiberglass still require the operators to confirm that the casing is in good condition and also the annular cement sheath is able to provide mechanical support and zonal isolation. The evaluation poses a challenge as the properties of the fiberglass casing are very different from those of the carbon steel casing. Studies were performed in 2018 to test the ultrasonic physics in fiberglass, and this paper describes the challenges and how we developed an innovative data acquisition, processing, and interpretation workflow to properly evaluate both the fiberglass casing condition and the annular cement condition. It was observed through surface experiments that the conventional ultrasonic technique applicable to carbon steel casing is not valid for fiberglass casing because the velocity and acoustic impedance of fiberglass are much lower than they are for steel; therefore, there is no resonance in fiberglass. A new interpretation workflow was developed and applied to raw data to build specific parameters for the fiberglass samples to determine the acoustic properties: acoustic impedance, attenuation factor, and velocity. It is for the first time that data have been acquired in a very large fiberglass casing. Fiberglass casings were run in a water well, and wireline acoustic logs were successfully acquired for cement and corrosion evaluation across 18-in. and 10-in. fiberglass casings. The interpretation workflow was applied to raw field data, and a comprehensive cement map and corrosion answer products were obtained with an acceptable quality control level. The paper will review the data from three wells. This innovative data acquisition, processing, and interpretation workflow can be deployed in wells for decision making prior to completion and production. The new method also opens up future opportunities for the evaluation of noncarbon steel casings, and, with knowledge of mechanical and acoustic properties, the method can be adapted to perform a full evaluation. This method is expected to provide valuable information for wells planned to be completed with fiberglass casing.