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 will seriously affect the safe exploitation of oil and gas. Self-healing cement slurry has the advantage of timely response to repair micro-cracks. When micro-cracks are generated， the self-healing agent is triggered to repair micro-cracks in time. As a potential self-healing agent in cement-based materials， sodium silicate can react with calcium hydroxide （Calcium hydroxide， CH） to form hydrated calcium silicate （Calcium-silicate-hydrate，C-S-H）. Microcapsule technology is usually used to encapsulate sodium silicate. However， the compatibility between microcapsules and cement paste is poor. To overcome this problem， this paper aims to use inorganic porous mineral diatomite with rich pore structure and excellent physical and chemical properties to adsorb sodium silicate to prepare diatomite-based self-healing materials and to explore its effect on the self-healing properties of oil well cement.
Methods Diatomite-based self-healing materials were prepared using the vacuum impregnation method. The diatomite-based self-healing materials were characterized by scanning electron microscope （SEM）， infrared spectrometer （FTIR）， and 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 incorporation of diatomite-based self-healing materials. The self-healing mechanism of diatomite-based self-healing materials was analyzed by X-ray diffraction analysis （XRD），thermal analysis （TG） and SEM.
Results and Discussion It was found that the number of pores on the sample surface after adsorption was significantly reduced compared with that before adsorption， and most of the pores were filled. BET analysis also showed that the pore volume and average pore size after adsorption were smaller than before adsorption. Combined with FTIR analysis， it was confirmed that the adsorption material in the pores of diatomite was sodium silicate. Then， diatomite-based self-healing materials were added to cement at different mass fractions of 0%，3%，6%，9%， and 12%. The 14 d compressive strength of the sample with 9% content was （39. 56±1. 98） MPa， which was 17. 95% higher than that of the pure cement sample. At the same time， the self-healing experiment of cement stone after the Brazilian splitting method was carried out. The compressive strength of the sample with 9% content reached （36. 90±1. 85） MPa after 14 d of self-healing， which was 99. 57% higher than that of the pure cement sample after 14 d of self-healing. The permeability of the sample with 9% content was 0. 42 mD after 14 d of self-healing， and the permeability reduction rate was 75. 44%， which was 40. 94% higher than that of the pure cement sample. The XRD test analysis of the material at the crack surface of the sample showed that the content of CH in the material at the crack surface of the diatomite-based self-healing material was lower than that of pure cement. The results of TG analysis showed that the CH content in the crack surface of the diatomite-based self-healing material was lower than that of the pure cement sample， and the C-S-H content was higher than that of the pure cement sample. Combined with SEM analysis， it was confirmed that the self-healing product of diatomite-based self-healing material at the crack of cement stone was C-S-H.
Conclusion The preparation and characterization of a self-healing material for oil well cement based on sodium silicate and diatomite 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 by the 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 diatomite-based self-healing material in oil well cement was 9% （mass fraction）. Diatomite-based self-healing materials exhibited good dispersibility and stability in oil well cement slurry， which could promote the self-healing of micro-cracks in oil well cement stone. The preparation process of diatomite-based self-healing materials was simple， and the compatibility with cement paste could be solved using inorganic porous materials， which provided a reference for further research on intelligent repair of micro-cracks in the cement sheath.
Keywords：sodium silicate； diatomite； oil well cement； microfractures； 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
