Direct CO2 Mineralization Through Oilwell Cementing

Abstract Cement production industry alone produces about 7% of the total anthropogenic CO2 around the world. Therefore, utilization of some carbon dioxide (CO2) in the construction of oilwell is a great way to recycle and contribute to decarbonization effort. The concept of recycling and utilization of CO2 has been realized to be applicable to both oilwell and civil engineering constructions including 3D printed structures. It is envisioned that there is potential of utilizing a total of up to 0.4Gt CO2 or over 1% of total global CO2 by incorporating into cement and Concrete systems. Portland cement hydration produces 15% Ca(OH)2 (Calcium Hydroxide or Portlandite). All these Calcium Hydroxide have potential to be directly mineralized to CaCO3 by blending with CO2. We have developed a proprietary laboratory size blender that can blend CO2 at up to 1000psi. Testing allows us to monitor irreversible conversion of CO2 to CaCO3. We were able to design Oilwell pumpable slurry formulations using CO2 blending technology with up to 15-20% enhanced compressive strength compared to commercially available technology without the use of carbonation, such as water extended, and/or silica fume based. CO2 acts as a cement setting accelerator which enables us to eliminate the use to traditional ones like CaCl2 or NaCl especially at temperature below 160°F and at lower slurry density. In addition, up to 70% reduction of the amount of Viscosifier like Xanthan gum or Hydroxyethylcellulose (HEC) has been realized. Laboratory testing has been performed to optimize CO2 mineralization efficiency without affecting the mechanical integrity of cement. Rheology, Free fluid and Thickening Time have been used to monitor and optimize slurry properties. Compressive strength measurement has been performed to ensure the mechanical integrity of cement. Direct incorporation of CO2 into the matrix of cement blends reduces the hardening time or waiting on cement (WOC) significantly which is another way of reducing loss of net productive time (NPT) towards sustainability. In addition, it also maximizes the amount of CO2 can be utilized in this process without compromising wellbore integrity. CO2 induced cement setting acceleration has potential to be applicable in both deepwater and permafrost cementing wherein lower bottomhole temperature demands large amounts of inorganic accelerators. The CO2 blending into oilwell cementing is a novel process and has great potential to directly mineralize CO2 without affecting the mechanical properties of cement sheath while concurrently eliminating/reducing chemical additives like accelerator/viscosifier.