刘 涛¹ ，张宏波² ，白云飞³ ，梅开元¹ ，张春梅¹ ，程小伟¹

刘涛，张宏波，白云飞，等. 煅烧菱镁矿对油井水泥石综合性能的影响［J］. 中国粉体技术，2024，30（6）：1-11.

LIU Tao ， ZHANG Hongbo， BAI Yunfei， et al. Effect ofmagnesite calcination methods on comphresiveperformance of oilwell cement stone［J］. China Powder Science and Technology，2024，30（6）：1−11.

基金项目：国家自然科学基金项目，编号：42207206。

第一作者简介：刘涛（2000—），男，硕士研究生，研究方向为固井水泥石的膨胀性能。E-mail：571355219@qq. com。

通信作者简介：程小伟（1977—），男，教授，博士，博士生导师，四川省学术和技术带头人后备人选，研究方向为先进胶凝材料与其在固井材料中的应用。E-mail：chengxw@swpu. edu. cn。

摘要：【目的】 解决油井水泥在水化过程中因体积收缩而导致水泥环出现微裂缝、进而出现一系列固井作业安全问题。【方法】 以菱镁矿为原料，采取不同的煅烧工艺制备具有不同活性的氧化镁膨胀剂（magnesia expansive agent， MEA），探讨煅烧工艺对MEA的微观结构和活性的影响，研究掺加不同活性MEA的油井水泥石的膨胀性能、抗压强度和渗透率性能。【结果】 菱镁矿煅烧温度为 900 ℃、煅烧时间为 30 min时，菱镁矿出现欠烧现象，制得的 MEA虽然活性较高，但膨胀性能较弱，水泥石的14 d线性体积膨胀率仅为5. 37‱；菱镁矿煅烧温度为1 200 ℃、煅烧时间为90 min时生成的MEA活性较低，MEA水化所需诱导时间较长，水泥石体膨胀量较小，水泥石的14 d线性体积膨胀率仅3. 26‱。【结论】 活性较高且有效成分多的MEA水化产生较大的膨胀力会破环水泥石的内部结构，综合考虑掺MEA水泥石的膨胀性能、力学性能、渗透率性能，菱镁矿最优煅烧方法为煅烧温度1 100 ℃、煅烧时间90 min。

关键词：油井水泥；氧化镁；煅烧菱镁矿；微观结构；综合性能

Abstract

Objective In oil drilling， shrinkage and fracture issues in cement slurry are particularly prominent. Due to the high temperature and pressure during the cementing process， significant shrinkage occurs. The volume shrinkage can create micro-cracks in cement sheath， compromising its bonding strength with the borehole wall and casing， and as well as the integrity of the cement sheath. These issues can cause annular channeling，resulting in pollution and loss of oil and gas resources. The use of expansion agents is an important means to avoid cracksin cement sheath.

Methods The studyused magnesite from Hebei Province as raw material. Magnesite powder was calcined in an electric furnace to obtain different active magnesia expansive agent （MEA）. MEA activity and microstructure were tested to establisha relationship between them. A comprehensive performance evaluation of cement slurry methods with different MEA activitieswas carried out，measuring linear volume expansion rate， compressive strength， and permeability of the cement stone.

Results and Discussion During calcination， magnesite initially decomposed into MEA grains. With the growth of MEA grains，their arrangement became more regular， reducing the crystal defects and limiting their deformation，thereby decreasing activity. With increasing calcination temperatures and extended holding times， the diffraction peaks of MEA graduallysharpened and the diffraction intensity increased， indicating a more complete structure. At the same calcination temperature， the longer the holding time， the more sufficient the decomposition of magnesite. As the temperature reached above 1 000 ℃， grain size increased，resulting in a denser MEA structure with lower lattice distortion. Increasing the temperature from 900 ℃ to 1 200 ℃， the grain size increased from 43. 92 nm to 126. 32 nm. At 1 000 ℃，extending the holding time from 30 min to 90 minincreased the grain size from 54. 11 nm to 115. 57 nm. When magnesite was calcined at 900 ℃ for 30 min， the resulting magnesite exhibitedsigns of insufficient calcination. Although the obtained MEA had high activity， its expansion performance was weak， with a linear volume expansion rate of only 5. 37 ‱ after 14 days. When calcined at 1 200 ℃ for 90 min， the activity of MEA was low， with a longer hydration induction time and minimal expansion， and its linear volume expansion rate was only 3. 26 ‱ after 14 days. In the 14-day cement stone， two strength development trends were observed：（Ⅰ） continually increasing；（Ⅱ） increasing first and then decreasing. The 14-day cement stone calcined at 1 100 ℃ for 90 minachieved a compressive strength of 43. 20 MPa.

Conclusion The paper shows thata single MEA particle is composed of many aggregated MEA grains， sintered at high temperatures. Calcination temperature and time influence the microstructure of MEA， affecting grain size， lattice distortion， and specific surface area. Higher calcination temperatures and longer calcination timespromote the growth of MEA grains，leading to a more regular grain arrangement， reduced lattice defects， increased grain sizes， decreased lattice distortion， and ultimately reduced hydration activity. Although the MEA activity is the highest when calcinedat 900 ℃ for 30 min， the expansion rate of MEA cement paste is the lowest，due to the insufficient decomposition of magnesite and weak expansion performance. In contrast， at 1 200 ℃， magnesite decomposition is complete， with larger grain sizes， smaller lattice distortion， and greatly reduced activity. Although higher activity MEA can compensate for the larger cement shrinkage by providing greater expansion in a short time， the excessive expansion force can break the internal structure of the cement stone， thus affecting its mechanical properties.

Keywords：oil well cement； magnesium oxide； calcination method， microstructure， comprehensive property

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