Performance evaluation of structurally modified wellbore cement with graphene nanoplatelets undergone thermal cyclic loading

Abstract

Geothermal energy is identified as one of the alternatives to fossil fuels in global climate crisis and the effective efforts for net-zero carbon emissions by 2050. The potential of geothermal heat at high temperatures is yet to be unlatched thus requiring a novel approach in all aspects of wellbore technology including cementing. Understanding the characteristics of the geothermal system is critical as we aim to develop wellbore materials for these thermally and chemically challenged wells. Materials used require stability at high temperatures and chemical resilience in contact with geofluids, where ordinary Portland cement (OPC) is deteriorating due to low pH that leads to loss in overall mechanical strength. Recent studies have shown that adding graphene nanoplatelets (GNP) to OPC based materials can improve properties and reduce risks from mechanical failures. GNP effect on overall cement properties has been studied and experimental results show promising outcomes at very low concentrations (<1% bwoc), significantly impacting strength and stiffness of the cement. The Class-H cement is hydrated with and without, liquid and powdered GNP at 0.008% and 0.1% concentrations each and cured in approximately pH 13 Ca(OH)2 solution to examine the influence of GNP on cement hydration. All the samples were subjected to cyclic temperature loading between 20 °C and 110 °C at 95% RH following an 8-hour cycle for 7 and 28 days in an environmental chamber. These temperature cycles help us evaluate close to the subsurface conditions where enhanced geothermal systems undergo thermal changes over tens of thousands of times during a lifetime of a well. Following API RP-10B specifications, GNP in the powdered form (PG) prepared from environmental waste and a 99.5% carbon purity lab grade liquid dispersion GNP (LG) were used. 0% GNP (neat) control, 0.008%, 0.1% of PG and LG mix design cement samples were prepared. Results show that 0.1%LG samples hydrated for 28 days had greater dispersion of GNP 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 elastic modulus when compared to neat sample hydrated for 28 days thus proving its effectiveness for wellbore integrity with increase in hydration time.