Mitigating the Risks of Natural Fractures During Drill Cuttings/Produced Water Reinjection in Conventional Wells

Abstract Drilled Cuttings Reinjection (DCRI) is crucial in addressing environmental pollution and achieving a circular economy. However, the success of DCRI is hampered by the risks and uncertainties associated with unplanned natural fractures (NF). These NFs result from tectonic activities, which distribute them predominantly, particularly between South America and the Niger Delta. Consequently, slurry leakage via unplanned NFs poses a nontrivial challenge during DCRI. Developing practical steps to mitigate the risks of the NFs is a welcome development. Thus, this study presents a model that enables the operators to predict the density of NF (NFD) to mitigate the risk of slurry leakages. The authors combined geomechanical modelling with fracture mechanics to predict the NFD and used a vertical well in the Passive Continental Margin of the Gulf Coast for evaluation. The results suggest that the operators need to avoid high porosity intervals to mitigate the risks of NFs during DCRI. Such intervals possess lower compressive strength and tend to open up, enhancing slurry leakage. The NFD is higher around the wellbore than away; the near wellbore is a high-risk region. Consequently, the authors suggest the addition of siloxanes into the slurry to seal off high-porosity intervals, due to their chemical properties, including water-repelling capacity, unusual stability over a wide temperature range, low toxicity, and production of silicon carbide (SC) under inert combustion. SC has a high melting point of up to 2830°C, which can withstand high-temperature injections. However, the slurry need not contain alkali solution or molten iron to prevent SC solubility. Furthermore, a higher Poisson's ratio yields a higher NFD, and the decrease in slurry temperature leads to an increase in the NFD. Thus, the authors recommended that the operators should inject deeper into the well, strengthen the near wellbore region, ensure thermal equilibrium, and minimize vibrations in the wellbore.