Improved Wellbore Cement with Graphene Nanoplatelets for Primary and Plug and Abandonment Cementing

Abstract:

Primary cementing in geothermal and oil and gas wells are subject to high temperatures, high pressures, and corrosive fluids that can cause leakage and failure of the cement barrier by inducing permeation or microcracks of the cement barrier, allowing subsurface fluids to flow upward and contaminate aquifers and surface soil. Graphene is a high strength, lightweight material that can be added to cement in low quantities. 16.4ppg Class-H cement cores were made with less than 0.1% by weight of cement graphene added and cured at 90°C and 95% relative humidity, to simulate wellbore conditions. Hydrated cement was then examined with microscopy tools such as scanning electron microscopy (SEM) and powdered x-ray diffraction (XRD), and petrophysical and mechanical properties measured. Preliminary results show that the graphene nanoplatelets tend to gather in pores and space within the cement matrix. Graphene additive appeared to not affect the porosity of the cement but reduced permeability by approximately 35%. Shear strength was also increased by approximately 20% under triaxial loading at wellbore temperature and pressure. As graphene is a relatively new material and is still being explored in a wide range of fields, the underlining mechanism of how it improves cement properties has yet to be determined and accepted. A potential mechanism of the graphene nanoplatelets affecting cement properties such as strength and permeability could be that the presence of graphene in micropores, as it is the strongest material currently known, could strengthen and reinforce these weak and empty points. A further investigation is needed, as the study is in progress, to support this hypothesis to study these effects of graphene when added to the cement. The potential for a graphene additive to increase strength while reducing brittleness in cement materials could have a large impact in geothermal/oil and gas, but in a wide range of applications as well.