Experimental study of saturated porous medium fracturing by abrupt pressure drop

It has been proposed that rock fracturing can be obtained by the powerful and fast pressure discharge at some boundary of the rock (fracture, borehole). The fracturing related with rapid pore pressure discharge looks as a “fracturing wave”.  Laboratory experiments allow to evaluate the main characteristics of the phenomena and to estimate conditions for the fracturing. Experimental data on the fracturing process were obtained with the help of transparent pressure-drop setup (plexiglass tube with length 455 mm, inner diameter 60 mm, wall thickness 5 mm) using the weak-cohesive porous samples made from the sand wetted by glycerol. The tube ends were closed by brass covers equipped by pressure transducers. Additionally, nipples for the air pumping and decompression were mounted at one of the covers. The pressure was increased by air pumping in up to 0.35 MPa, then the pressure was released through solenoid valve with flow section 15 mm. Decompression rate was controlled by the diaphragms with different diameters: 2.8, 3.0, 3.4, 4.0, 4.8 mm. To observe the fracturing, high-speed camera with frame rate 1200 frames per second was used. The dependencies of maximum depth of the fracture formations and mean distance between the fractures on decompression rate were obtained. It was found that the number of fractures and the last fracture depth grow with the pressure drop rate, while the inter-fracture distance decreases.