LI Kun1，ZHANG Chunmei1，LIU Cheng2，MEI Kaiyuan1，HU Chen1，CHENG Xiaowei1
（1. School of New Energy and Materials， National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation， Southwest Petroleum University， Chengdu 610500， China；2. Exploration Division， Southwest Oil and Gas Field Branch， Chengdu 610000， China）
Abstract
Objective The expansion of micro-cracks in oil well cement seriously affects the safe exploitation of oil and gas. Self-healing cement slurry can respond timely to repair these micro-cracks. When micro-cracks form， the self-healing agent activates to repair them. As a potential self-healing agent in cement-based materials， sodium silicate reacts with calcium hydroxide （CH） to form calcium silicate hydrate （C-S-H）. Microcapsule technology is usually used to encapsulate sodium silicate. However， these microcapsules have poor compatibility with cement paste. To overcome this problem， this paper aims to use diatomite， an inorganic porous mineral with an intricate pore structure and excellent physical and chemical properties， to adsorb sodium silicate to prepare diatomite-based self-healing materials. Also， the paper explores their effect on the self-healing properties of oil well cement.
Methods Diatomite-based self-healing materials were prepared using the vacuum impregnation method. The materials were characterized by scanning electron microscopy （SEM）， Fourier-transform infrared spectroscopy （FTIR）， and an automatic surface area and pore structure analyzer （BET）. The self-healing effect was evaluated by comparing and analyzing cement stone's compressive strength， recovery rate， and permeability before and after the incorporation of diatomite-based self-healing materials. The self-healing mechanism was analyzed using X-ray diffraction （XRD）， thermal analysis （TG）， and SEM.
Results and Discussion After adsorption， it was found that the number of pores on the sample surface was significantly reduced compared to pre-adsorption， and most of the pores were filled. BET analysis also showed that the pore volume and average pore size were smaller after adsorption. FTIR analysis confirmed that sodium silicate filled the pores of diatomite. Then， diatomite-based self-healing materials were added to cement at different mass fractions of 0%， 3%， 6%， 9%， and 12%. The 14-day compressive strength of the sample with 9% content was （39. 56±1. 98） MPa， 17. 95% higher than that of pure cement. At the same time， the self-healing experiment of cement stone after the Brazilian splitting method was carried out. After 14-day self-healing， the compressive strength of the 9% cement sample reached （36. 90±1. 85） MPa， 99. 57% higher than that of pure cement. Its permeability was 0. 42 mD after 14-day of self-healing， and the permeability reduction rate was 75. 44%， 40. 94% higher than that of pure cement. XRD analysis of the cracked sample surface showed a lower CH content in diatomite-based self-healing material compared to pure cement. TG analysis further confirmed that CH content was lower， and C-S-H content was higher than that of the pure cement. SEM analysis confirmed that the self-healing product of the diatomite-based self-healing material at the cement stone cracks was C-S-H.
Conclusion The preparation and characterization of a sodium silicate and diatomite-based self-healing material for oil well cement were reported in this paper. The prepared samples were analyzed by SEM， FTIR， and BET. The diatomite-based self-healing materials could be successfully prepared using vacuum impregnation method. At the same time， the diatomite-based self-healing material was added to the cement to explore its effect on the self-healing performance of the oil well cement stone. The optimum content of the material in cement was 9% （mass fraction）. Diatomite-based self-healing materials exhibited good dispersibility and stability in cement slurry， which could promote the self-healing of micro-cracks in oil well cement stone. Their simple preparation process and compatibility with cement paste suggest that inorganic porous materials can provide a reference for further research on the repair of micro-cracks in cement sheath.
Keywords：sodium silicate； diatomite； oil well cement； micro-crack； self-healing
Get Citation:Li Kun， Zhang Chunmei， Liu Cheng， et al. Preparation and characterization of oil well cement self-healing materials based on sodium silicate and diatomite［J］. China Powder Science and Technology，2024，30（3）：64−75.
Received:2023-09-28.Revised:2023-11-28,Online:2024-04-15。
Funding Project:国家自然科学基金项目，编号：42207206；文昌 9-7 油田多分支复杂结构井固井方案及工作液体系研究项目，编号：CCL2022RCPS0702PSN。
First Author:李锟（1999—），男，硕士生，研究方向为固井自愈合材料。E-mail：1194074067@qq. com。
Corresponding Author:
张春梅（1977—），女，副教授，硕士生导师，研究方向为固井新材料研发。E-mail：200531010045@swpu. edu. cn。
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及其在固井中应用。E-mail： chengxw@swpu. edu. cn。
DOI：10.13732/j.issn.1008-5548.2024.03.006
CLC No:TE256； TB4； TQ324.8 Type Code:A
Serial No:1008-5548（2024）03-0064-12
