![]() Additional experiments were performed to evaluate the coefficient of friction for the different interface surface preparations used. ![]() The frictional shear stress that the interface can support without slippage appears to be critical in determining fracture growth across the interface. It was found that as the interface surface friction coefficient was decreased, the normal stress had to be increased for a hydraulic fracture to cross the interface. Lubricants and surface roughening were used to vary the frictional properties of the interfaces. Prismatic blocks of the rock materials to be studied were held adjacent to one another in a hydraulic press so that a normal stress was set up across their mutual interface. The fracturing fluid was oil (viscosity ~ 300 cp) injected into the rock through high-pressure steel tubing. The materials used in these studies were Nugget sandstone from Utah (3 to 6% porosity) and Indiana limestone (12 to 15% porosity). The purpose was to evaluate under which conditions the hydraulic fractures would cross the interface. Small-scale laboratory experiments were performed to study the growth of hydraulically driven fractures in the vicinity of an unbonded interface in rocks.
0 Comments
Leave a Reply. |