Field data show that fracturing in poorly-consolidated rocks is not adequately represented by traditional models for brittle, linear-elastic rocks. This is not unexpected since unconsolidated sands do not exhibit brittle- elastic behavior.In addition, sands have very low tensile and shear strengths.

A model is presented for the propagation of "fractures" in unconsolidated sands.The model departs radically from current models in that brittle fracture mechanics is not used.Instead the propagation of pore pressure is computed and the porosity and permeability of the sand is specified as a function of the effective stress.This results in the creation of an anisotropic zone of increased porosity and permeability along the plane of maximum in-situ stress (normal faulting stress regime) or at a certain angle to it (strike slip faulting regime). This region of enhanced porosity defines a "fracture" in unconsolidated sands.The physics of creation and propagation of this oriented, high permeability zone, is modeled for the first time.

It is shown that in-situ stress anisotropy and shear failure play a very important role in determining the dimensions of this fracture zone. In addition, the permeability anisotropy generated due to the stress anisotropy in the sand is the critical driving force behind the creation of the oriented "fracture".

During the hydraulic fracturing of an unconsolidated formation, a high permeability zone (channel or fracture) will form in response to the difference in situ horizontal stresses and the decrease in the net effective stress near wellbore.To correctly model the fluid distribution, the fluid flow behavior must be coupled to the mechanical behavior of the sands. Based on the coupled geo-mechanics and reservoir simulation (model, iterative-coupled 2-D finite difference software is developed to simulate the strain, stress change due to the injection. Based on the constitutive relationship of permeability and porosity, we modeled permeability and porosity as a function of effective stress.