Application of a New Concept for Enhanced Well Integrity Evaluation in Unconventional Completions with Fiberglass Casings in Kuwait

Abstract

The cement bond evaluation of wells completed with fiberglass casings has always been a challenge due to the very large difference in the acoustic behavior of fiberglass with respect to steel. This problem was faced in Kuwait when ultrasonic image logs were recorded for some wells completed with fiberglass casings that gave highly erratic readings and posed significant challenges with interpretation when applying the conventional methods. It was critical to field development engineers to have the precise status of the cement bond around fiber casings to ensure integrity of casing from encroachment of formation fluids in the zone of interest. This, in turn, required that cement bond logs do accurately and precisely evaluate the cement integrity. The logging company along with drilling engineers resolved the challenge of interpretation innovatively by an integrated approach of ultrasonic and sonic data. The approach used a recently introduced platform to develop a new concept of data processing in which high-accuracy interpretation of the cement bond behind fiberglass was made possible. As has been observed through field and laboratory experiments, the conventional ultrasonic technique applicable to carbon steel pipes has been proven to be invalid in fiberglass tubulars because the velocity and acoustic impedance of fiberglass are much lower than steel; therefore, there is no resonance in fiberglass. A new method and interpretation tool was developed and applied to raw data to build on parameters specific to the fiberglass samples used in Kuwait through surface tests to identify the acoustic properties of fiberglass: acoustic impedance, attenuation factor, and velocity. Standardized processing parameters were established for consistency and accuracy to determine the actual pipe thickness, radius and cement acoustic impedance from ultrasonic measurements in many wells. The resulting logs from the new method were found to be satisfactory by field development and they were then applied to earlier drilled wells to validate the results. The advanced platform used for data processing and integration has provided a reference interpretation prototype of log response in fiberglass casings in different scenarios to accurately determine whether cement bond is poor, good, or non-existing. A further investigation of ultrasonic late waveform arrivals could elaborate unique information on casing standoff and centration inside the wellbore. A reasonable casing integrity evaluation was also feasible from the new method resulting in good estimate of valid pipe thickness and acoustic impedance. This paper illustrates the application and evolution of the new method, which enables advanced data processing and integration to provide robust images even beyond cement and pipe integrity. It has been implemented in many wells, and it has provided a significant improvement in quality of logging results in fiberglass casing wells. The new interpretation model can be successfully adopted wherever there is similar material used for casings.