ZHENG Yijie，GONG Peng，DENG Zhuoran，HE Xin，ZHANG Chunmei，MEI Kaiyuan，CHENG Xiaowei

（School of New Energy and Materials， National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation， Southwest Petroleum University， Chengdu 610500， China）

Abstract

Objective Using CO₂ injection to enhance oil and gas recovery is crucial in the carbon neutralization process. However，the pres⁃ence of supercritical CO₂ in CCUS wells poses higher demands on the corrosion resistance of wellbore cement. Magnesia olivine，characterized by abundant sources and low cost， has been extensively studied in the field of construction cement. Yet， research on enhancing the resistance of wellbore cement to CO₂ corrosion using magnesia olivine is relatively limited.In this study，con⁃ducted in the unique environment of CCUS wells，corrosion experiments will be carried out using supercritical CO₂-saturated solutions. Various testing methods，including compressive strength， permeability，X-ray diffraction（XRD），thermogravimetric analysis（TGA），and scanning electron microscopy（SEM），will be employed to investigate the optimal dosage of magnesia oliv⁃ine and its role in the micro-mechanism of corrosion resistance. This research aims to provide new theoretical and practical sup⁃port for enhancing the resistance of wellbore cement to CO₂ corrosion，contributing technological solutions towards achieving the“carbon neutrality and peak carbon”goals.

Methods Utilizing layered olivine magnesium with an average particle size of 23 μm as an additive and cement slurry with a den⁃sity of 1. 92 g/cm³， oil well cements with varying additive concentrations（0，0. 5，1，1. 5，2，2. 5，3 wt.%）were formulated and cured following GB/T 19139—2012. Under conditions of 150 °C and 50 MPa CO₂ pressure，compressive strength and per⁃meability were tested for both blank samples and samples with magnesium olivine，aiming to identify the optimal dosage of mag⁃nesium olivine. Thermal Gravimetric Analysis（TGA），X-ray Diffraction（XRD），and Scanning Electron Microscopy （SEM）were employed to analyze the impact and mechanisms of magnesium olivine on the CO₂ corrosion resistance performance of the cement slurry.

Results and Discussion Formulated cement slurries with different concentrations （0，0. 5，1，1. 5，2，2. 5，3%） of magnesium olivine. No significant impact on the density of oil well cement slurries was observed with the addition of magnesium olivine.Maintained good fluidity of the slurry，indicating favorable rheological properties. Conducted testing under conditions of 150 °C and 50 MPa CO₂ pressure. Magnesium olivine addition enhanced the compressive strength of cement both before and after corro⁃sion， showing a 35. 47% increase at 2% olivine concentration. The compressive strength initially increased and then decreased with higher olivine concentrations. Improved compressive strength attributed to the filling of micro-pores by magnesium olivine，enhancing cement density. Super-critical CO₂ corrosion resulted in the formation of calcium carbonate（CaCO₃）on the cement surface.The presence of magnesium olivine contributed to the reduction of Ca（OH）₂ and the formation of dense CaCO₃enhanc⁃ing the cement's resistance to CO₂ corrosion. The addition of 2% magnesium olivine demonstrated the highest compressive strength before and after corrosion. Extended corrosion testing up to 28 days revealed a gradual decrease in compressive strength for both control and magnesium olivine-added cement. Magnesium olivine-added cement showed better long-term performance，with slower deterioration in compressive strength compared to the blank cement stone，which improved by 193. 71%. The perme⁃ability of the cement was effectively reduced by magnesium olivine，indicating improved resistance to CO₂ corrosion. XRD and TGA analysis confirmed the presence of magnesium olivine and the formation of carbonates（CaCO₃）in the corroded cement.The addition of magnesium olivine reduced Ca（OH）₂ content and influenced the types of carbonate phases formed during corro⁃sion. SEM images illustrated the microstructural changes in cement，showing the impact of magnesium olivine on the formation of corrosion products. Magnesium olivine addition resulted in a denser microstructure， reduced pore formation，and better over⁃all cement integrity. The observed improvements in cement performance were attributed to the role of magnesium olivine in hin⁃dering the penetration of CO₂，optimizing microstructure， and promoting the formation of stable carbonate phases. The optimal addition of 2% magnesium olivine was identified as providing the best balance between enhancing compressive strength and resisting CO₂ corrosion in oil well cement. The study demonstrates the potential of magnesium olivine as an effective additive for improving the durability and performance of oil well cement in the context of super-critical CO₂ corrosion.

Conclusion The optimal addition of 2% magnesium olivine was identified as providing the best balance between enhancing com⁃pressive strength and resisting CO₂ corrosion in oil well cement. The study demonstrates the potential of magnesium olivine as an effective additive for improving the durability and performance of oil well cement in the context of super-critical CO₂ corrosion.

Keywords：magnesium olivine； high temperature and high pressure； supercritical CO₂； corrosion； oil-well cement

Get Citation:ZHENG Y J， GONG P， DENG Z R， et al. Effect of magnesium olivine on CO₂ corrosion resistance of oil well cement［J］. China Powder Science and Technology，2024，30（2）：151−163.

Received：2023-10-02，Revised：2023-11-29，Online：2024-02-20。

Funding Project：国家自然科学基金项目，编号：42207206。

First Author：郑怡杰（1999—），男，硕士生，研究方向为超临界CO₂环境下油井水泥石抗腐蚀性能。E-mail：2817950245@qq. com。

Corresponding Author：程小伟（1977—），男，教授，博士，四川省学术和技术带头人，博士生导师，研究方向为先进胶凝材料与其在固井中应用。 E-mail： chengxw@swpu. edu. cn。

DOI：10.13732/j.issn.1008-5548.2024.02.013

CLC No：TE256；TB4；TQ324.8                  Type Code：A

Serial No：1008-5548（2024）02-0151-13