Abstract

When a well reaches the end of its life-cycle, it should be permanently plugged and abandoned. Geopolymers have recently attracted attention as potential alternative materials to cement, and hence, have the potential to be used as permanent barriers. This paper presents a brief overview of geopolymers and their chemo-physical properties and how they can be applied to the plug and abandonment (P&A) operation.

To give a better understanding of geopolymers, Class C fly ash-based geopolymers were prepared and examined. Fly ashbased geopolymers were produced by the alkali –activation of the Class C fly ash with an activator solution (a mixture of NaOH and sodium silicate solution). The NaOH solution was prepared at three concentrations of 6, 8 and 10 mol/L and it was mixed with the sodium silicate solution at a mass ratio of 1 in order to prepare the activator solution. The fly ash-C to liquid mass ratio was 1.9, typically producing final densities in the range of 2.44 s.g. In order to investigate the effect of curing temperature on the mechanical property of the obtained geopolymer, specimens were cured at two different temperatures (87 °C and 125 °C) under a pressure of 5000 psi. This work studies the effect of curing temperature and NaOH concentration on the mechanical properties of the specimens. Uniaxial compressive strength (UCS) tests and Ultrasonic cement analyzer (UCA) tests were carried out to measure the compressive strength development of the specimens. Scanning Electron Microscope (SEM) images were taken to study the microstructure of the specimens. Measurements of pH of ground specimens was performed and based on the obtained results pH alters during the curing time. These measurements will found a basis for selecting the correct material for the P&A operation.

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