Cognizing Integrity of Ultra-Light Weight Cement Slurry Placement Across Fractured Reservoir using Advanced Flexural Technology in TAL Block

Abstract Ensuring well barrier and cement integrity has remained an operation of utmost importance throughout the life cycle of a well with numerous challenges and proposed solutions associated with it. Due to advancements in the design of cement slurry when subjected to various rock properties and downhole environments, the methods for cement evaluation also evolved from traditional measurement by cement bond log-variable density log (CBL-VDL) to ultrasonic and advanced flexural measurements. This paper presents the application of integrated cement evaluation (ICE) using flexural technology for the evaluation of a 9 lbm/gal ultralight weight cement slurry, which was used across the naturally fractured limestone reservoir of the Well X-1 in the TAL block [Kohat plateau, province of Khyber Pakhtunkhwa, Pakistan] to avoid any losses due to high annular pressure as in the case of conventional cement slurries. By examining flexural technology in depth, this paper presents the advantage of using advanced flexural waveform measurements over traditional ultrasonic measurements and cement bond logs. To resolve the uncertainty and incomplete picture of material present directly behind the casing, the ultrasonic and flexural technology are combined to not only provide complete azimuthal coverage but to accurately distinguish between the three states of matter quantitatively by reducing the reliability on thresholds. The flexural wave emitted by the logging tool's transmitter propagates along the casing in the flexural mode and provides an evaluation of the attenuation during propagation along the casing in the form of a solid, liquid, gas (SLG) map. This measurement improved the accuracy of characterizing the material in the annulus, which allows for discriminating very light cement from liquid beyond what is attainable by basic ultrasonic measurement alone. A case study from Pakistan of using ultralight weight (ULW)- cement slurry is presented where the objective was to provide a clear picture of the cement barrier and to alleviate the ambiguity from conventional cement evaluation methods. As a result, a novel and advanced measurement technique was implemented to provide the answers. The results demonstrated and proved the superiority of this technology by resolving the micro debonding puzzle and rectifying 30 to 40% of liquid as solid cement on the SLG map. This integrated approach saved the operator from costly remedial jobs, provided confirmation for zonal isolation, and aided in optimizing well completion.