High temperatures (HT) and the corrosive environment make the design of a geothermal drilling fluid a highly complex task. The presence of HT exacerbates the problems due to thermal degradation. Geothermal aquifers usually combine high-temperature and complex chemistry, making them highly corrosive. Although geothermal drilling fluids are exposed to thermal degradation, research of the effect on mud rheological properties in temperatures near or above 149°C (300°F) is limited.

In this study, a High Pressure-High Temperature (HPHT) rheology setup was used to measure drilling fluids' properties up to 204.4°C (400°F). Rheological behavior of viscosity, density, lost circulation, and alkalinity control additives were analyzed at HT. It was found experimentally that Bentonite alone is thermally stable at HT. In contrast, Caustic Soda showed a tendency to gelate at temperatures above 93.3°C (200°F), adversely affecting mud rheology. Alkalinity control materials to replace Caustic Soda were evaluated. Among them, Lime presented the best thermal stability at 204.4°C with a range of variation of 0.0024 Pa.s (2.4 cP) on apparent viscosity after three consecutive tests. Besides, it was tested 11 different lost circulation materials (LCM) for understanding their rheological behavior at HT. It was found that HT has less impact on fine granular materials rheological behavior with an average increase of 17.7% compared with the baseline. In contrast, flaky, fibrous, and coarse granular materials presented a more apparent impact in WBM rheology with a deviation of 166% compared with the baseline.

高温 (HT) 和腐蚀性环境使地热钻井液的设计成为一项非常复杂的任务。HT的存在加剧了由于热降解引起的问题。地热含水层通常结合了高温和复杂的化学性质，使其具有很强的腐蚀性。尽管地热钻井液会发生热降解，但在接近或高于 149°C (300°F) 的温度下对泥浆流变特性影响的研究是有限的。

在这项研究中，高压-高温 (HPHT) 流变学装置用于测量高达 204.4°C (400°F) 的钻井液的特性。在 HT 上分析了粘度、密度、堵漏和碱度控制添加剂的流变行为。实验发现，单独的膨润土在 HT 下是热稳定的。相比之下，苛性钠在高于 93.3°C (200°F) 的温度下表现出凝胶化的趋势，对泥浆流变学产生不利影响。评估了替代烧碱的碱度控制材料。其中，Lime 在 204.4°C 时表现出最好的热稳定性，连续 3 次测试后表观粘度变化范围为 0.0024 Pa.s (2.4 cP)。此外，还测试了 11 种不同的堵漏材料 (LCM)，以了解它们在 HT 下的流变行为。发现HT对细颗粒材料流变行为的影响较小，与基线相比平均增加17.7%。相比之下，片状、纤维状和粗粒状材料对 WBM 流变学的影响更明显，与基线相比偏差为 166%。