水力压裂支撑剂嵌入深度计算方法

Calculation method of proppant embedment depth in hydraulic fracturing

针对水力压裂支撑剂嵌入问题,基于支撑剂嵌入岩体的力学过程,建立支撑剂嵌入岩体的本构方程,并结合岩体-支撑剂体系的接触应力分析,提出考虑弹塑性变形的支撑剂嵌入深度计算方法,基于该方法分析了嵌入深度的影响因素。相对于弹性模型,新方法计算结果更接近于实验测量结果,预测更加可靠,且更便于进行理论计算和分析。研究表明:支撑剂嵌入岩体的过程主要发生弹塑性嵌入;支撑剂单层铺置条件下铺置浓度越高嵌入深度越小,多层铺置条件下增大支撑剂铺置浓度不会改变嵌入深度;支撑剂嵌入比例越大,承压支撑剂越多,支撑剂嵌入深度越小;高闭合应力情况下支撑剂嵌入更加显著,流体压力下降会显著增大支撑剂嵌入深度;增大支撑剂粒径或岩石与支撑剂弹性模量比值,会减小支撑剂嵌入深度。

For the issue of proppant embedment in hydraulic fracturing, a new calculation method of embedment depth considering elastic-plastic deformation was proposed based on the mechanism of proppant embedment into rocks by combining proppant embedment constitutive equations and contact stresses on the rock-proppant system. And factors affecting embedment depth of proppant were analyzed using the new method. Compared with the elastic embedment model, the results calculated by the new method match well with the experimental data, proving the new method is more reliable and more convenient to make theoretical calculation and analysis. The simulation results show the process of proppant embedment into rocks is mainly elastic-plastic. The embedment depth of monolayer proppants decreases with higher proppant concentration. Under multi-layer distribution conditions, increasing the proppant concentration will not change its embedment depth. The larger the proppant embedment ratio, the more the stress-bearing proppants, and the smaller the embedment depth will be. The embedment depth under higher closure stress is more remarkable. The embedment depth increased with the drawdown of fluid pressure in the fracture. Increasing proppant radius or the ratio of proppant Young＇s modulus to rock Young＇s modulus can reduce the proppant embedment depth.