Material characterization of graphene enhanced Class-H cement under thermal cyclic conditions

Abstract

Geothermal heat harvesting is the process of extracting heat from the earth’s subsurface where it is trapped below the diverse rock formations to be converted into usable energy. Cementing of the drilled wells requires the use of materials that are stable at high cyclic temperatures as production ranges between 160°C and +300°C. Ordinary Portland Cement a brittle material (OPC) when mixed with additives can provide improvement to the mechanical stability and enhance fracture resistance at these conditions. One such additive that has gained interest in other fields and applications, but not much explored in cementing field due to its unreactive and hydrophobic nature, is graphene nanoplatelets (GNPs). This study focuses on mixing GNPs with Class-H cement in very low concentrations of 0.1% or less by weight of cement (bwoc) and evaluating the performance and effectiveness in fracture prevention when undergone thermal cycling between 20 °C and 110 °C, 95% relative humidity when hydrated for 7 and 28 days in pH 13 Ca(OH)₂ solution. GNPs in the form of powder (PG) prepared from the environmental waste and a 99.5% carbon purity lab grade liquid dispersion GNPs (LG) were used. 0% GNPs (neat) control, 0.008%, 0.1% of PG and LG mix design cement samples were prepared following API 10B specifications. Results show that 0.1%LG samples hydrated for 28 days had greater dispersion of GNPs with a notable increase in the ductile behavior out of all the designs tested. There is a 13.21% decrease in permeability, 27.77% decrease in hardness and 50.71% decrease in elasticity when compared to neat sample hydrated for 28 days thus proving its effectiveness for wellbore integrity with increase in hydration time.