Device and method for the determination of rock fracture toughness of a reservoir and the effect of confinement on the fracture toughness

A method for determining fracture toughness (KIC), and the effect of confinement on said fracture toughness, of specimens under controlled conditions, wherein the method comprises the following steps:

• providing a device comprising a frame;
• a hydraulic pressure testing rig supported by the frame and comprising a pressure gauge, a lever and a pressure diaphragm;
• a storage tank for storing hydraulic fluid, supported by the frame;
• and a pressure chamber supported by the frame, wherein the test specimen is placed to be subjected to hydrostatic pressure through conduits that connect said pressure chamber with the storage tank in fluid communication;
• preparing the specimens by machining a notch in each one of the specimens;
• testing each one of the specimens in the pressure chamber, wherein each test comprises applying hydraulic fluid under controlled pressure to the specimen notch for generating a stress state, and measuring the pressure at which the specimen fractures;
• and
• processing the results obtained from the performed tests and calculate the fracture toughness using equation (1):
• KIC=Y·σ·√{square root over (π·a)} (1)
• where Y is a shape factor for membrane stresses, a is the notch depth and σ is the applied fluid pressure.