Experimental Study of Hydraulic Fracture Initiation in Colton Sandstone

摘要

We performed laboratory scale experiments for the study ofrnhorizontal fluid driven fracture initiation from an open-holernsection. In order to clarify the role of material microstructurernand fluid infiltration, we used viscous Newtonian fluids torninitiate penny shaped fractures from radial notches in blocksrnof natural sandstone. We varied the fluid viscosity andrninjection rate over ranges allowing for significant fluid lossesrntoward the dry porous rock. For low efficiency fluids, thernfracture propagation was characterized by non-monotonicrnpressure variations. We propose a formulation of the problemrnof hydraulic fracture initiation in an elastic homogeneousrnpermeable material. Our model accounts for fluid lossesrntoward the rock and a cohesive zone at the fracture tip. Wernperformed dimensional analysis in order to lump the physicalrnparameters into meaningful dimensionless groups. Scalerneffects concerning the fluid efficiency, decompression effectsrnand material failure could be predicted from dimensionalrnanalysis and corroborated with experimental observations. Wernalso propose a numerical solution for this model. Thernnumerical results compare well with experimental results. Thisrnwork provides a proper scaling for hydraulic fracturerninitiation. This scaling is necessary for comparing laboratoryrnscale results to field observations.