The thermal properties of set Portland cements – a literature review in the context of CO2 injection well integrity

Abstract

Depleted hydrocarbon reservoirs are a promising target for CO2 sequestration. Injection of cold CO2 into such geological reservoirs will cause thermal stresses and strains in wellbore casings, cement seals and surrounding rock, which may lead to the creation of unwanted pathways for seepage. Joule-Thomson effects could potentially produce freezing conditions. The design of CO2 injector wells must be able to cope with these thermal loads. While numerical modelling can be used to develop our understanding and assess the impact of thermal processes on wellbore integrity, such analyses require reliable input data for material properties, such as those of the cement seals. This critical review provides an overview of existing lab measurements and theoretical considerations to help constrain the thermal behaviour of Portland cement under relevant subsurface conditions. Special attention is given to the i) thermal conductivity, ii) specific heat capacity, and iii) coefficient of thermal expansion. Influences on these properties of factors such as a) temperature, b) pressure, c) mixing water-to-cement ratio, d) extent of hydration, e) porosity, and f) pore fluid saturation are discussed. Our review has shown that lab datasets obtained under relevant downhole conditions are limited, constraining the input for numerical assessment of wellbore cement integrity.