Abstract: During the drilling of deep tight oil and gas reservoirs, polymer-based additives are susceptible to high-temperature degradation, resulting in the deterioration of properties such as rheology and filtration loss in bentonite-free water-based drilling fluids. To address the limitations of traditional high-temperature stabilizers, carbon microspheres (Cy-CMSs)were synthesized via a green hydrothermal carbonization process using β-cyclodextrin as a precursor. The structure of Cy-CMSs was comprehensively characterized, and their effects on the rheological and filtration loss properties of various polymer solutions, experimental base slurries of the AM-AMPS-NVP (Cop-1)copolymer, and bentonite-free water-based drilling fluids were evaluated before and after thermal treatment at different temperatures. The underlying mechanisms of Cy-CMSs were also investigated. The study demonstrated that Cy-CMSs possess abundant hydrophilic oxygen-containing functional groups on the surface and hydrophobic polyfuran rings in the core, exhibiting a typical core-shell structure. Traditional biopolymers and high-temperature-resistant synthetic polymers degrade and lose their functionality after exposure to high temperatures of 120-140 ℃ and 180-200 ℃, respectively. However, the addition of 0.5%Cy-CMSs results in an apparent viscosity retention rate exceeding 80%after hot rolling. When Cy-CMSs were incorporated into the Cop-1 experimental base slurry, the apparent viscosity retention rate reached up to 95%after hot rolling at 240 ℃. Furthermore, under long-term static aging conditions at 220 ℃, the degradation of performance was significantly delayed. After adding 0.5%Cy-CMSs to the bentonite-free water-based drilling fluid formulated with biopolymers, both the rheological and filtration properties remained stable after hot rolling at 160 ℃. Cy-CMSs effectively absorb dissolved oxygen in the drilling fluid, reducing its concentration to the order of 10^-2mg/L, while also scavenging free radicals generated under high temperatures, thus preventing the thermal oxidative degradation of polymers. In addition, Cy-CMSs can form bridged structures with polymers, further enhancing their thermal stability. Cy-CMSs significantly improve the high-temperature and even ultra-high-temperature thermal stability of water-based drilling fluids, outperforming the traditional high-temperature stabilizer Na₂SO₃. This provides a novel approach for regulating the high-temperature rheological and filtration properties of bentonite-free water-based drilling fluids used in deep and tight oil and gas reservoirs.

Key words: water-based drilling fluid, high-temperature stability, hydrothermal carbon microsphere, free radical scavenging, bridged structure

摘要： 深层致密油气储层钻井过程中,聚合物类处理剂容易高温降解而导致无黏土相水基钻井液流变和滤失等性能恶化。针对传统高温稳定剂的不足,以β-环糊精为原料,通过"绿色"水热炭化反应制备出炭微球Cy-CMS,对其结构进行综合表征,分别考察不同温度作用前后Cy-CMS对不同聚合物溶液、AM-AMPS-NVP(Cop-1)共聚物实验基浆和无黏土相水基钻井液流变性和滤失性的影响,并探讨其作用机理。研究表明,Cy-CMS表面含有丰富的亲水性含氧官能团,内部为疏水性聚呋喃环,为典型的核壳结构。传统的生物聚合物和抗高温合成聚合物分别在120~140 ℃和180~200 ℃作用后降解失效,加入0.5%Cy-CMS热滚后表观黏度保持率均大于80%。Cop-1实验基浆中加入Cy-CMS,240 ℃热滚后其表观黏度保持率最高达95 %, 220 ℃长期静置老化条件下其性能恶化得到明显延缓。以生物聚合物构建的无黏土相水基钻井液中加入0.5%Cy-CMS,160 ℃热滚前后流变性和滤失性保持稳定。Cy-CMS可吸收钻井液中溶解氧并将其降至10^-2mg/L数量级,同时有效清除高温下产生的自由基,避免聚合物热氧化降解。此外,Cy-CMS还可与聚合物形成桥连结构,进一步提高聚合物的热稳定性。Cy-CMS能显著提高水基钻井液高温甚至超高温作用下的热稳定性,明显优于传统高温稳定剂Na₂SO₃,为深层致密油气无黏土相水基钻井液高温流变和滤失性能调控提供了全新途径。

关键词: 水基钻井液, 高温稳定性, 水热炭微球, 自由基清除, 桥连结构