A Volcanic Tephra-Based Non-Portland Cement System for Well Cementing Sustainability

Summary Although Portland cement (PC) is extensively used in oil and gas well cementing for different applications such as zonal isolation and plugging, it does have technical and environmental drawbacks. PC is responsible for approximately 8% of global carbon dioxide (CO2) emissions and consumes massive energy while manufacturing. Geopolymer cements, which are made from nontraditional, non-PC ingredients, have garnered attention as potential candidates for oilwell cementing due to their low CO2 footprint and less energy consumption. This work introduces a proposed non-PC system that totally replaces PC using volcanic tephra (VT) and an alkaline solution. The study started by collecting, crushing, and sieving VT until it became a fine VT powder. Rheological properties, thickening time, unconfined compressive strength, and dynamic elastic properties were also assessed for the developed formulation. Sedimentation evaluation was conducted using the API method and nuclear magnetic resonance (NMR). The experimental evaluation included thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, and particle-size distribution. The developed 15.8 ppg VT-based geopolymer used a 4 M sodium hydroxide (NaOH) solution and VT only. The 24-hour unconfined compressive strength was 2,900 psi, with a Poisson’s ratio of 0.29 and a Young’s modulus (YM) of 1.11 Mpsi. The developed formulation had a thickening time of 3.5 hours at a bottomhole circulation temperature of 170°F without using any retarder. The density variation between the top and bottom sections was only 0.65%. This work introduces a new cement system made of VT without any processing except milling and sieving. This reduces the overall carbon footprint and costs of oilwell cementing operations.