Traditional hydraulic fracture simulators do not take into account the compositional, thermal, and phase behavior effects that are crucial to the success of energized fractures.  This implies that until recently there has not been a systematic, simulation based approach for energized hydraulic fracture design. 

Traditional water-based fracturing fluids are not ideally suited for use in tight, depleted or water sensitive formations.  In such situations, if the drawdown pressure does not overcome the capillary forces in the formation, the liquids leaking-off will remain trapped in the invaded zone around the fracture face.  A fluid is energized by adding a gas component to the fracturing fluid.  Gas addresses the water trapping problem by creating a high gas saturation in the invaded zone, thereby facilitating gas flowback. 

In this paper, a fully compositional fracture simulator is used to evaluate different designs for energized fractures.  It is shown that gases with high solubility in aqueous solutions perform significantly better than gases that are not.  CO2 has higher solubility than N2, and therefore outperforms N2 in most cases.  Because N2 is less soluble in water, additional measures are needed to make sure it is present in the invaded zone.  This can be done by delaying flowback and allowing the gas phase to penetrate into the invaded zone.  Adding methanol to the liquid phase can increase the solubility of CO2 and reduce clay swelling in some formations resulting in more effective fracture treatments.

It is shown that energized fluids should be applied to rocks when the drawdown pressure is insufficient to remove the liquid.  This corresponds to a drawdown pressure of  200 psi for 0.1 md formations,  500 psi for 0.01 md, and  1500 psi for 0.001 md.

Simulations show that under a wide range of reservoir conditions, foam qualities from 30 to 50% are optimum because they allow enough gas to saturate the liquid to maximize gas flowback and they yield long fractures.  Higher quality (up to 70%) may be necessary if shorter and wider fractures are preferred. 

Use of a compositional fracture simulator allows us for the first time to systematically design energized fracture treatments.  Simulations provide a cheap and effective method of predicting fracture performance and reaching conclusions that allow the design of better performing fractures.