Mechanical performance of oil-well cement slurries cured and tested under high-temperatures and high-pressures for deep-well applications

Abstract

The American Petroleum Institute testing standard (API TR 10TR7) recommends determining the mechanical performance of oil-well cement slurries in an ambient-temperature testing environment. However, with exploration and exploitation resources moving toward deep formations, cement slurries for oil, gas, and geothermal wells are increasingly being utilized in high-temperature and high-pressure (HTHP) in-site formations. It is unknown if the current standard is suitable for assessing the mechanical performance of cement slurry under in-site HTHP conditions in deep wells. To fill this research gap, an innovative experimental platform was developed for this study to mimic the in-site HTHP environments in real production wells; then oil-well cement slurries were cast, cured, and tested at elevated temperatures (i.e., 90 °C, 115 °C, 140 °C) and the confining-pressure (i.e., 20 MPa). The mechanical performance of cement slurries was evaluated under triaxial compression and cyclic loads. The microstructures of cement slurries were also studied. This study revealed that the high-temperature testing environment accelerated the crack propagation and stress drop of stress-strain curves, decreased the failure stress (up to 14.0 %), Young's modulus (up to 16.4 %), and Poisson's ratio (up to 31.7 %), and resulted in more brittle characteristics of cement slurry samples. This study confirmed that using the current standard will significantly overestimate the mechanical properties of oil-well cement slurries in HTHP environments. The authors suggest updating the standard to take HTHP environments into consideration, which should ultimately meet the increasing demands of developing deep oil, gas, or geothermal wells.