Toward Understanding the Crevice Corrosion Susceptibility and Kinetics of P110 Steel in the Supercritical CO2 Fracturing Shale Oil Production Environment

The susceptibility of P110 steel to crevice corrosion was initially assessed in a 10% CO2-saturated shale oil-produced solution by using weight loss measurements and surface analysis, simulating corrosion induced by CO2 leakage at the casing/cement interface. Subsequently, the crevice corrosion kinetics were investigated by electrochemical techniques. All corrosion experiments demonstrated that corrosion occurred once a crevice was physically created. However, the corrosion behavior differed from classic critical crevice solution, and IR drop crevice corrosion theories, which typically involve acidification, destruction of corrosion products and an acceleration of corrosion inside the crevice. In this study, hydrogen reduction is used as the cathodic reaction rather than oxygen reduction. The surface morphology and protectiveness of the corrosion product formed inside the crevice are different from those outside the crevice. A thin and well-crystallized corrosion product formed inside the crevice, whereas a thick layer of corrosion product without discernible crystallinity was visible outside the crevice. A distinct difference was noticed in the three crevice areas, where slight corrosion was inside the crevice, but severe corrosion occurred outside the crevice, and a deep groove appeared at the crevice mouth. The strong galvanic effect between the inside and outside crevices triggered crevice corrosion. The electrode inside the crevice acted as the cathode, and the electrode outside the crevice worked as the anode, with the potential difference between them increasing over time. The crevice corrosion phenomenon in this study is attributed to alkalization inside the crevice, and a corresponding mechanism is proposed. Crevice corrosion may diminish or even vanish in the long-term operation of shale oil fields after supercritical CO2 fracturing if the cathode and anode do not reverse over time.