The Fracking process or method, is done by pumping fracking fluid into a wellbore at a rate sufficient to increase pressure downhole to exceed that of the fracture gradient of the Shale rock. The rock then cracks and the fracking fluid continues farther into the rock, extending the crack still farther, and so on. To keep this fracture open after the injection stops, a solid proppant, commonly a sieved round sand, is added to the fluid. The propped fracture is permeabile enough to allow the flow of formation fluids to the well.The location of fracturing along the length of the borehole can be controlled by inserting composite plugs, also known as bridge plugs, above and below the region to be fractured. This allows a borehole to be progressively fractured along the length of the bore without fluid leaking through previously fractured regions. Fluid and proppant are introduced to the working region through piping in the upper plug. This method is commonly referred to as "plug and perf."
Typically, fracking is performed in cased wellbores and the zones to be fractured are accessed by perforating the casing at those locations.
Microseismic monitoring is commonly used to estimate the size and orientation of hydraulically induced fractures. Microseismic activity is measured by placing an array of geophones in a nearby wellbore. By mapping the location of any small seismic events associated with the growing hydraulic fracture, the approximate geometry of the fracture is inferred.
Tiltmeter arrays, deployed on the surface or down a well, provide another technology for monitoring the strains produced by Fracking.
