Improved Depleting Sand Fracture Model

An improved depleting sand fracture model was derived in this work using finite element methods and putting into consideration the effect of pore pressure and production on in-situ stresses. Sets of governing equations from commercial finite element simulator COMSOL multi-physics(TM) were used to obtain a model which compares well with existing fracture model, majorly based on the Mohr's coulomb failure criterion. A constant overburden load was used since its value majorly depends on depth, and the formation is assumed to be fixed at the bottom. The reservoir is assumed to be depleting at a constant rate with no water injection to assist pressure with average porosity of 25% and average permeability of 251mD at beginning of production. The reservoir compacted as it produces and in turn porosity and permeability reduces over the years of observation. Fracturing was observed to be much easier for the depleted reservoir due to the fact that horizontal stresses, which might have created friction, reduces as the reservoir is being produced signifying that for depleted reservoirs small fracture pressure is required. Fractures created are observed to propagate in the direction of the maximum horizontal stress and perpendicular to the direction of the minimum horizontal stress.