硅酸盐钻井液泥包形成的趋势研究

硅酸盐钻井液因其优异的防塌抑制性常应用于泥页岩地层，但其在钻进过程中极易发生钻具泥包现象。笔者通过分析硅酸盐钻井液极易产生泥包的原因，选取用膨润土制成2.0 mm～3.2 mm的泥球来模拟钻屑用于实验研究，利用自制直径为25 mm的钢球，老化罐的滚动模拟井下钻进情况，通过硅酸盐加量、硅酸盐模数、膨润土含量、KCl加量及不同防泥包剂对硅酸盐钻井液体系产生泥包的实验研究，探讨了不同因素对硅酸盐钻井液产生泥包的程度及趋势的影响。结果表明，硅酸盐模数对泥包影响不大；随着硅酸盐含量的增加，泥包程度呈上升趋势，但加量超过9%后泥包程度相差不大，建议加量在3%～5%之间；随着膨润土加量的增加，泥球的直径呈先减小后增大的趋势，膨润土加量为1%时，泥球直径最小；KCl在一定浓度内降低泥包的产生，过量的KCl反而会促进泥包生成，最佳浓度为3%～6%；加入3%防泥包快钻剂WETMINE能有效防止钢球泥包的产生。通过与钻井液体系流变性相结合，优选出能最大程度减少钻具泥包的硅酸盐钻井液体系关键外加剂的加量，为选择合适的外加剂提供参考依据。

Study on Bit Balling in Drilling with Silicate Drilling Fluid

Silicate drilling fluid is always used to drill mudstone and shale formations because of its excellent inhibitive capacity. A drawback of the silicate drilling fluid is the ease of bit balling. By analyzing the causes of bit balling using silicate drilling fluid, a laboratory experiment was designed to study the factors affecting the bit balling tendency of using silicate drilling fluid. In the experiment, mud balls of 6-10 mesh, made from bentonite, were used to simulate drilled cuttings. Steel balls of 25 mm and aging cells were used to simulate the conditions prevailing downhole. Several factors, such as the concentration of silicate, the module of the silicate, bentonite concentration, KCl concentration and addition of different bit balling preventing agents were studied for their effects on the occurrence of bit balling. The experimental results showed that the effect of the module of the silicate on bit balling can be ignored. The likelihood of bit balling increased with increase in the concentration of silicate; when the concentration of silicate was more than 9%, the severity of bit balling did not change greatly anymore. The concentration of silicate was suggested to be between 3% and 5%. With the increase of the bentonite content, the diameters of the mud balls reduced first and then increased. When 1% bentonite was used in the mud, the diameter of the mud balls became minimum. KCl at certain range of concentration can mitigate the occurrence of bit balling; excessive use of KCl on the other hand accelerate the occurrence of bit balling. The optimum concentration of KCl was 3%-6%. 3% WETMINE (a bit balling preventing agent and fast drilling agent) in the silicate drilling fluid can effectively prevent the occurrence of bit balling on the surface of the steel balls. Taking into account the rheology of the drilling fluid, the concentrations of the key additives used in the silicate drilling fluid were determined to provide a reference for selecting suitable additives for the silicate drilling fluid.