响应面法优化纳米材料稳定的泡沫钻井液

为提高泡沫钻井液的稳定性，向体系中引入纳米材料，并研究了纳米材料润湿性对于泡沫质量的影响。根据Box-Behnken Design设计原理，采用三因素三水平响应曲面法，优化了起泡剂BS-12、亲水性纳米SiO2和增黏剂XC的加量，探究了它们之间交互作用对于泡沫综合指数的影响，并以此为基础研制了泡沫钻井液体系。结果表明，纳米材料润湿性会显著影响不同类型起泡剂的泡沫质量，疏水性纳米材料能够提高阴离子起泡剂SDS的泡沫稳定性，但对两性离子起泡剂BS-12的泡沫起泡量和半衰期呈现负相关关系，亲水性纳米材料才能提高两性离子起泡剂BS-12的泡沫稳定性；通过响应曲面优化设计得到的最优浓度配比为：0.6% BS-12+4%纳米SiO2+0.3% XC。响应曲面分析表明，对于泡沫综合指数的显著性影响程度，纳米材料浓度 > 起泡剂浓度 > XC浓度；纳米稳定的泡沫钻井液体系性能评价表明，该体系表观黏度为42mPa·s，密度为0.81 g/cm3，半衰期达60 h，能长时间保持性能稳定，抑制性强，线性膨胀率较清水下降65%，储层保护效果好，煤岩岩心气测渗透率恢复率在90%以上，携岩效果好，岩屑和煤屑的沉降速度较清水降低92%以上，能够满足现场煤层气钻井的需要。

Study on Foam Drilling Fluid Stabilized with Nanomaterials Optimized with RSM

Nanomaterials have been used to improve the stability of foam drilling fluids, and the effects of the wettability of the nanomaterials on the foam quality were studied using three-factor three-level response surface methodology (RSM) in accordance with the Box-Behnken Design principle. In the studies the concentrations of the foaming agent BS-12, the hydrophilic nanoSiO2 and the viscosifier XC were optimized, and the effects of their interaction on the comprehensive performance of the foam were investigated. A new foam drilling fluid was designed based on these studies. It was found in the studies that the wettability of the nanomaterials remarkably affected the foam quality of the foaming agents. Hydrophobic nanomaterials was able to enhance the stability of the foam produced with an ionic foaming agent SDS. Increased treatment of the hydrophobic nanomaterials decreased the foam quality and halflife of the foam produced with an amphoteric foaming agent BS-12. The optimized foam mud was obtained using RSM design, which is: 0.6%BS-12 + 4%Nano SiO2+0.3%XC. RSM analysis showed that order of magnitude of effect of the concentrations of the three agents on the comprehensive performance of the foam is: nanomaterial > foaming agent > XC. Laboratory evaluation showed that this foam drilling fluid had apparent viscosity of 42 mPa·s, density of 0.81 g/cm3, half life of 60 h, meaning that the foam drilling fluid is able to sustain its stability for a long time. The foam drilling fluid also showed strong shale inhibitive capacity; the linear expansion rate is 65% lower than that of clean water. The recovery rate of coal rock core gas permeability is over 90%, and settling velocity of rock and coal cuttings in the foam drilling fluid was reduced by at least 92% compared with clear water, indicating that the foam drilling fluid had both good reservoir protection performance and good cuttings carrying capacity. The results of the performance evaluation test showed that this foam drilling fluid is able to satisfy the needs of coal-bed methane drilling.