Analysis Behind Casing to Assess Zonal Isolation and Casing Deterioration in a High Pressure Exploratory Well - ABC to Z of Well Integrity Barrier Evaluation

Abstract

The UHP exploratory well subject of this study faced with myriad challenges, including fishing, side-tracking, and other undesirable incidents with consequences to the 9-7/8" production casing. Torque and drag analysis, preliminary casing wear simulations, and actual drilling parameters pointed towards multiple uncertainties concerning barrier integrity. Consequently, a multi-physics evaluation was conducted including well-integrity logs in a combination of thickness-mode with flexural-mode of the casing. Signals from these independent measurements are then processed to provide robust interpretation of solid-liquid-gas behind casing using acquired flexural attenuation and acoustic impedance data. In addition, casing wear is quantified by thickness changes measured through the resonance frequency of the waveform and represented in the form of a joint-by-joint corrosion summary, reporting the average metal loss. Furthermore, propagation of flexural wave-fronts as it leaks to the third interface is tracked to produce a unique image of the annulus geometry in terms of casing eccentricity and acoustic velocity of the medium. Subsequently, the former, provides a quantifiable, unique in-situ casing standoff measurement to be used for centralization evaluation. Application of the developed data-integrated workflow allowed for comprehensively analyzing well integrity barrier condition. Cement barriers were assessed with confidence by flexural imaging, which were difficult to determine solely with pulse-echo. Additionally, annulus imaging using third interface- echo (TIE) helped in characterizing the potential causes of casing wear and quality of cement behind casing by providing actual in-situ casing standoff. It was observed that casing wear was at the low side of the wellbore where the casing had the least standoff as shown by flexural waveform TIE arrivals. Moreover, high percentage of metal loss was correlated to regions with centralization lower than 40-50%. Integration of these results with casing side forces and remaining casing strength (under worst case scenario) was performed to evaluate casing endurance for future drilling, production, and injection operations.