The most important data for designing a fracture treatment are the in-situ stress profile, formation permeability, fluid-loss characteristics, total fluid volume pumped, propping agent type and amount, pad volume, fracture-fluid viscosity, injection rate, and formation modulus. It is very important to quantify the in-situ stress profile and the permeability profile of the zone to be stimulated, plus the layers of rock above and below the target zone that will influence fracture height growth.
Dealing with and exploiting fracturing of rock has been part of mining engineering for hundreds of years, but the analysis of fracture of rock or other materials has only developed into an engineering discipline since the mid 1940s . In petroleum engineering, fracture mechanics theories have been used for more than 50 years. Rock fracture mechanics is about understanding what will happen to the rocks in the subsurface when subjected to fracture stress. Much of what is used in hydraulic fracturing theory and design was developed by other engineering disciplines many years ago. However, rock formatons cannot often be treated as isotropic and homogeneous. For example, their porous and fluid filled nature can require that poroelastic theory be used for some problems. There are a number of important parameters to consider in the fracturing of rock. Some of these are fracture toughness, in situ stress, Poisson's ratio, and Young's modulus.
In general, hydraulic fracture treatments are used to increase the productivity index of a producing well or the injectivity index of an injection well. Hydraulic fracturing can increase the flow rate of oil and/or gas from low-permeability reservoirs, increase the flow rate of oil and/or gas from wells that have been damaged, connect the natural fractures and/or cleats in a formation to the wellbore, decrease the pressure drop around the well to minimize sand production, enhance gravel-packing sand placement, decrease the pressure drop around the well to minimize problems with asphaltine and/or paraffin deposition, increase the area of drainage or the amount of formation in contact with the wellbore, and connect the full vertical extent of a reservoir to a slanted or horizontal well. The most critical parameters for hydraulic fracturing are formation permeability, the in-situ stress distribution, reservoir fluid viscosity, skin factor, reservoir pressure, reservoir depth, and the condition of the wellbore. The safety meeting also should be used to discuss the well completion details and the maximum allowable injection rate and pressures, as well as the maximum pressures to be held as backup in the annulus.