I am trying to understand PKN and KGD models for hydraulic fracturing. I am wondering why equations for fracture width and length does not include 'breakdown pressure' (pressure at which fracture initiates? The formula for fracture length for KGD include shear modulus, injection rate, viscosity, fracture height and time only. Why there is not a threshold value, after which fracture initiates in this formula?
Pl study the formula carefully. The breakdown pressure is taken into account in PK, PKN 3D and Psuedo. 3D method.
@Anirbid Sircar Here is the formula for fracture length used in literature. Can you please tell me where is breakdown pressure in this final solution?
https://earthscience.stackexchange.com/questions/10273/measuring-fracture-length-and-width-using-pkn-and-kgd-models-for-hydraulic-fract
In the development of the PKN and KGD models for hydraulic fracturing, it was stated that the average net pressure in the fracture would greatly exceed the minimum pressure for propagation, unless the fluid flow injection rate was extremely small or the fluid had an unrealistically low viscosity. Therefore, under typical fracturing conditions, the pressure resulting from fluid injection is practically larger than the minimum pressure (breakdown pressure) required to create or extend a stationary fracture. This justifies neglecting fracture mechanics effects in the models. Furthermore, it was stated that the fracture would continue to extend after pumping stopped, until either leak-off affects further extension or the minimum pressure for fracture propagation is reached.
@Azeez Aregbe, Thankyou very much. Can you plesase refer me to a text where this thing is mentioned in more detail.
You are welcome. You can find more details in 'Reservoir Stimulation' by Michael J. Economides and Kenneth G. Nolte.
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