Coal powders, as cuttings, invade the drilling fluid along a coal seam during coalbed methane development, thereby changing the properties of the drilling fluid. Therefore, this work aims to investigate the influence of coal powders on drilling fluid performance. The powders of lignite, anthracite, and contrasting shale were added to a water-based polymer drilling fluid. Then, the rheology, filtration, lubricity, and adhesiveness were measured, and the natural degradation, as well as the wettability were further evaluated. The results show that some parameters of the drilling fluid, including viscosity, lubrication coefficient, adhesion coefficient, contact angle, and surface tension, increase after adding coal powders, while other parameters, such as filtration loss and natural degradation, decrease. Compared with lignite and shale, anthracite powders, with the lowest mineral content, exhibit the smallest change in the rheological property, lubricity, adhesion, and natural degradation of the drilling fluid. Moreover, the content and size of the coal powders generally have opposing effects on the drilling fluid. When the coal powder content reaches 3 wt.%, the surface tension and contact angle of the drilling fluid show more evident changes than other parameters. Based on the analysis of the stress intensity factor, the drilling fluid with coal powders exceeding 100 mesh can reduce the capillary force in microfractures, and in combination with other factors (such as reduced filtration loss and sealing and supporting of the microfractures), improves wellbore stability. Therefore, coal powders with suitable particle sizes and concentration levels are expected to become a new drilling fluid material to protect coal field reservoirs.

中文翻译：

---

煤粉对水性聚合物钻井液性能影响的试验研究

在煤层气开发过程中，煤粉作为岩屑沿煤层侵入钻井液中，从而改变钻井液的性质。因此，本工作旨在研究煤粉对钻井液性能的影响。将褐煤、无烟煤和对比页岩粉末添加到水基聚合物钻井液中。然后，测量流变学、过滤性、润滑性和粘附性，并进一步评估自然降解以及润湿性。结果表明，加入煤粉后，钻井液的黏度、润滑系数、粘附系数、接触角、表面张力等参数增加，而其他参数，如滤失量和自然降解等则降低。与褐煤和页岩相比，无烟煤粉的矿物含量最低，对钻井液的流变性能、润滑性、粘附性和自然降解等方面的变化最小。此外，煤粉的含量和粒度通常对钻井液具有相反的影响。当煤粉含量达到3wt.%时，钻井液的表面张力和接触角的变化比其他参数更明显。根据应力强度因子分析，超过100目煤粉钻井液可降低微裂缝中的毛细管力，并结合其他因素（如降低滤失和微裂缝的封闭支护等），改善井筒稳定。所以，