A Non-Portland Cement System: A Step Forward Towards Sustainability of Oil Well Cementing

Although ordinary Portland cement (OPC) is widely used in oil well cementing for different applications such as zonal isolation and plugging, it does have technical and environmental drawbacks. Portland cement is responsible for approximately 8% of the global carbon dioxide (CO2) emissions and consumes massive energy while manufacturing. Geopolymer cements, which are made from non-traditional, nonOPC ingredients, have garnered attention as potential candidates for oil well cementing due to their low CO₂ footprint, and less energy consumption. This work introduces a proposed non-Portland cement system that totally replaces Portland cement using volcanic tephra (VT) activated by an alkaline solution. The study started by collecting, crushing, and sieving VT until getting fine VT powder. Rheological properties, unconfined compressive strength (UCS), Poisson's ratio (PR), and Young's modulus (YM) were also evaluated for the developed formulation. Sedimentation evaluation was conducted using the API method. The developed VT based geopolymer used sodium hydroxide (NaOH) solution and VT. The 24 h UCS was 3,132 psi with a PR of 0.29 and a YM of 7.69 GPa. It has a thickening time of 3.5 h without using any retarder at 170°F. The density variation between the top and bottom sections was only 0.65 %. This work introduced a new cement system made of VT without any processing except milling and sieving. This reduces the overall carbon footprint, and costs of oil well cementing operations. Moreover, it solves some technical problems associated with the use of Portland cement.