煤层气复杂结构井可降解钻井完井液实验

为了解决煤层气复杂结构井钻井过程中钻井安全与煤层保护的矛盾,研制了可降解的钻井完井液,分析了其常规性能和降解性能,并分别采用解吸率法和渗透率恢复率法评价了钻井完井液对煤层解吸能力和渗流能力的保护效果.通过室内实验优选了适用于复杂结构井的可降解钻井完井液中的增黏剂、降失水剂和降解剂,并确定了钻井完井液的配方.钻井完井液各项常规性能良好,可有效携岩和保护井壁.钻井完井液具有良好的降解性能:加入浓度为2.0%~4.0%的降解剂后,3 h内降解率可达85%以上;降解完成后固相残渣少.钻井完井液可以有效保护煤层解吸能力和渗流能力:具有和清水一样良好的煤层解吸能力保护效果;煤样在不同返排压差下的渗透率恢复率均在60%以上,最高可达100%左右,且渗透率恢复率随着返排压差的增大而增大.图2表7参11

Laboratory research on degradable drilling-in fluid for complex structure wells in coalbed methane reservoirs

In order to address the contradiction between drilling safety and coalbed damage control, a degradable drilling-in fluid (DIF) was developed for complex structure wells in coalbed methane (CBM) reservoirs. Its conventional properties and degradability were analyzed, and the desorption rate and return permeability methods were presented to evaluate its protection on coal desorption and seepage performance. Laboratory experiments were carried out to optimize thickening agent, fluid loss additive and filtrate reducer in DIF which is applicable to complex structure wells, and to determine the DIF formula. The DIF, with good conventional properties, can effectively carry cuttings and protect sidewall. It is also degradable. The experiment results show that DIF degradation rate is up to 85% in three hours when degradation agent is added at a concentration of 2.0% to 4.0%, and there is less solid residue after degradation. The DIF can effectively protect the seepage performance and also coal desorption, similar to clean water. The return permeability is all above 60% at different flow back pressure and the return permeability becomes bigger with increase of the flow back pressure, the maximum is up to 100%.