天然裂缝压裂液滤失模型

Study on fluid loss model for natural fracture

在裂缝性储层水力压裂过程中,天然裂缝在水力裂缝的作用下产生剪切滑移或张开,使压裂液的滤失量显著增加,从而增大了施工风险。目前的压裂液滤失模型大多是针对均质储层的,不适用于裂缝性储层。为此,从天然裂缝内压裂液的动态滤失过程出发,描述了压裂液滤失的物理过程;根据压力连续及流体体积守恒原理,建立了天然裂缝压裂液滤失模型;结合模型求解思路和方法,编制了计算程序。研究结果表明,压裂液性质、天然裂缝性质和施工参数等对压裂液的滤失影响较大,重点模拟分析了充填带对滤失量的影响。天然裂缝压裂液滤失模型计算结果表明:当最大缝宽较窄时,存在最小滤失量的临界缝宽;当最大缝宽较大时,累积滤失量与临界缝宽成反比;增大充填物的体积浓度可减小压裂液滤失量;而增大充填带临界厚度会增大滤失量,但存在最佳临界厚度。

In the process of Hydraulic fracture in fractured formation,the interaction between hydraulic fracture and natural fractures made the natural fracture open or shear slip,which leads to the fluid loss in fractured reservoirs dramatically,at the same time,the hydraulic fracturing risk increased greatly.However,at present most of the leak-off models aims at homogeneous formation only.On the basis of natural fracture dynamic loss process,this paper builds a natural fracture leak-off physical model.Based on the combined pressure continuation and volume conservation,we proposed the leak-off mathematical model which is originated from microscopic understanding of the fluid leak-off mechanization of the fractured formation.We programed in the light of the idea and method shown above in this paper.The calculated results of model shows fracturing fluid,the natural fractures and construction parameters can affect fluid loss.Through calculating and analyzing the affecting factors,the conclusion is that the model can fit to practical project,and it has a strong engineering significance.