Abstract

Ordinary Portland cement (OPC) has been the material of choice for oil & gas well cementing and abandonment for many decades now. However, there are drawbacks to the use of OPC for cementing and abandonment purposes, particularly in wells with higher temperatures. OPC is brittle and does not re-heal when cracked. It is easily contaminated by mud and spacer fluids. Furthermore, it has relatively low tensile strength and low strength when bonding to rock formations and casing. Moreover, the production of OPC is the 2nd largest source of CO2 emissions in the world. At the CODA industry-affiliate consortium at the University of Texas at Austin dedicated to well construction, decommissioning and abandonment, work is ongoing to find technically superior alternatives to OPC. Particularly promising materials are so-called geopolymers, formed by activating an alumino-silicate material such as fly ash (a waste material that is often discarded) with an alkali. It was found that these geopolymer materials offer more ductile strength and failure behavior, considerable resistance to contamination, higher tensile strength and bond strength, and an ability to re-heal when damaged. The results obtained for geopolymers formed by activating flyash with potassium and sodium silicates indicate that these may be well-suited for achieving long-term thermal well integrity.

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