Role of Turbulent Flow in Generating Short Hydraulic Fractures with High Net Pressure in Slickwater Treatments

摘要

This paper provides an argument for considering turbulent flow for hydraulic fracturing using slickwater in shale reservoirs.It shows that the tendency of models that assume laminar fluid flow to over-predict fracture length and under-predict net pressure can be corrected by instead recognizing that the flow regime is turbulent for high rate,water-driven hydraulic fractures.Firstly,we provide a rationale supporting the appropriateness of assuming turbulent flow.Then,using a Perkins-Kern-Nordgren(PKN)fracture model and parameters similar to slickwater treatments in shale reservoirs,we show that the laminar flow model overpredicts fracture length and underpredicts fracture width and net pressure,compared to the turbulent flow model.The result,if indeed a hydraulic fracture grows in the turbulent fluid flow regime,is that matching the length with the laminar model requires input of an unreasonably large leak-off coefficient, resulting in an exacerbation of the underprediction of the wellbore pressure.On the other hand,the turbulent model is shown to be able,in principle,to account for short,high pressure hydraulic fractures without resorting to inflating the leak-off coefficient or compromising the calibration of the model to the wellbore pressure.