Abstract

Volume changes due to shrinkage are inherent to the hydration process of ordinary portland cement (OPC) and alkali-activated cementitious materials. Under elevated temperature and pressure conditions, as is the case in oil and gas wells, the internal stresses created by shrinkage can result in loss of zonal isolation and the need for expensive repairs.

This paper compares the early age shrinkage behavior of Class H OPC, alkali-activated Class F fly ash (referred to as geopolymer in this study), and geopolymer-hybrid (geopolymers incorporating drilling mud) slurries with up to 20% (by volume) synthetic based mud (SBM) contamination cured at 23°C and 50°C. In addition, the use of zinc and aluminum-based expansive agents to mitigate shrinkage was explored. Results from various test methods characterizing shrinkage behavior show that (a) shrinkage increases with temperature for all cases, (b) geopolymers shrink less than OPC slurries at low temperature, (c) geopolymer shrinkage exceeds that of OPC slurries at higher temperatures, (d) the addition of SBM increases the shrinkage of both OPC and geopolymer slurries, and (e) the use of suitable expansive agents has the potential to neutralize shrinkage of both OPC and geopolymer slurries. The work also shows that the current set of ASTM and API shrinkage tests need to be augmented with a test that can be conducted at elevated temperature and pressure, particularly when testing expansive agents that generate gases. A proposal for a more relevant test is included.

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