On Quantitative Assessment of Effective Cement Bonding to Guarantee Wellbore Integrity

Abstract

Methane leakage due to compromised wellbore cement integrity may result in operational complications and environmental contaminations in oil and gas wells. In this work, the problem of fluid-driven fracture propagation at the cement interfaces is revisited by a thorough and comprehensive consideration of the non-uniform cement bonding to the formation along the wellbore. While previous works were mainly focused on discharge without attention to mechanical failure or mechanical failure without ties to seepage rate, here we couple these two analyses to provide a practical aspect of this approach. As revealed by cement evaluation logs, the quality of the cement behind the casing varies and may include flaws in the form of channels or pockets of mud residuals. A novel methodology, initiated with laboratory-scale cement bonding properties using the push-out test, is introduced to estimate the cohesive properties of the cement interface, considering mud removal and mud residuals in the rock. Then the measured cohesive properties are applied to a field-scale numerical model with an embedded cohesive layer between cement and formation to evaluate the susceptibility of the wellbore to develop cement debonding. The excessive fluid pressure at the casing shoe is assumed to be the source for the fracture initiation. The proposed numerical model has been tested against actual SCP field tests for validation purposes. This model may estimate the geometry of leakage pathways and predict leakage flow rate within acceptable ranges. The effect of several key factors in the development of SCP due to the cement debonding is investigated. The results show that the early stage of SCP build up is controlled by the cohesive properties of the cement interfaces (i.e., cement properties), but the cohesive properties have minor effects on the stabilized pressure. The method proposed herein presents a method to evaluate the cement bond quantitatively to be further integrated in cement design.

Fluid Migration Characterization of Full-Scale Annulus Cement Sections Using Pressure-Pulse-Decay Measurements

“…Similar effective wellbore permeabilities have also been reported by Crow et al [12] and Kang et al [13]. When combined with a model for fluid migration along the wellbore, sustained casing pressure records can be used to assess properties of the migration paths and leakage rates [14].…”

Impact of microannulus on the efficiency of heat transfer in the bottomhole

“…In extreme cases, the microannulus encompasses the full circumference of the wellbore. However, in most cases, only part or the cement is affected, as it can be seen in cement evaluation logs (Vrålstad and Skorpa, 2020;Santos and Dahi Taleghani, 2021). To evaluate the effect of the size of the microannulus on the bottomhole temperature, different degrees of severity were evaluated, ranging from 0 (no microannulus) to 1 (full circumference).…”

“…Microannulus is a well-known issue in the oil and gas industry that can sometime harm production, cause fluid migration between different zones and lead to methane emission. Proper drilling practices, such as more effective mud removal techniques (Santos and Dahi Taleghani, 2021) and more accurate casing centralization (Liu et al, 2018), decrease the chance of failure at the cement interface. However, microannuli may still form, mainly due to the variations in pressure and temperature during or after the cementing process (Baumgarte et al, 1999).…”

Improving the Rheological and Mechanical Properties of Oil Well Cement Slurries Using Multiple Chemical Admixtures for Enhancing Zonal Isolation: A Laboratory Evaluation

“…Oil spills generate ecological disasters due to harmful substances other than financial catastrophes, particularly in marine areas. The oil industry has invested billions of dollars in developing mechanically driven equipment and supplies to enhance oil extraction and reduce oil and gas loss [3,26]. In any case, the reality is that it is difficult to address each new issue that arises.…”