Experimental and Numerical Evaluation of the Integrity of Cement and Geopolymer Under Low and Elevated Temperature Well Conditions

Abstract

ABSTRACT: Wellbores constructed in high-temperature environments require more reliable cement systems to overcome complicated near-borehole loads. In this study, we numerically evaluate the effect of temperature on the interfacial bond integrity of two cementitious materials - an industrial class expansive cement and a rock-based geopolymer based on their experimental triaxial test properties. The results from the triaxial test indicate that the test temperature did not have a significant impact on the mechanical properties of both types of materials except for the confined compressive strength. Geopolymer showed higher flexibility, higher Poisson’s ratio, and lower compressive strength than the industrial class expansive cement at both temperatures. From the numerical analysis, the results show that the most likely cement failure location is at 90° to the maximum in-situ stress on the casing-cement interface. Without considering pore pressure effects, cement crushing resulting from excessive compressive stress is the main reason for the inner interfacial debonding. The test temperature has a significant influence on hoop stress. High test temperature results 13 – 45% increase in the hoop stress. Radial stress was insignificantly influenced by the test temperature. When test temperature changes from 30 to 90°C, geopolymer experiences an 80% increase in hoop stress while the industrial class expansive cement only experiences a 1% increase. 1. INTRODUCTION Cement is one of the major barrier elements for maintaining well integrity. It is conventionally used for in primary, remedial and plug and abandonment operations. The loss of well integrity can lead to environmental risks, economic losses for the operator and even safety issues. Several factors can compromise cement integrity during its placement, these include but are not limited to poor cement displacement, fluid loss, mud contamination, etc. Despite the completion of a good cement job, fissures, cracks and microannuli may still develop long after well completion.