Abstract
Almost all commercial hydraulic fracture models are simulators that use injection variables such as fluids and proppants to predict fracture geometry. Totally different in both philosophy and approach are fracture design models which are aimed to first determine the optimum fracture geometry to maximize production (or injection) and then to establish the best way to achieve the desired geometry.
Starting with a treatment schedule, and with fracture mechanics, fluid mechanics and rock mechanics modeling of varying degrees of sophistication, fracture simulators predict the fracture geometry. While these models were originally using the classic 2D models they have evolved into pseudo-three-dimensional (p-3D) and, even, in some cases, fully three-dimensional (3D) models.
The same models are used to match the observed pressure in the field and because usually the original intent was to match net fracturing pressure they have incorporated among other things, near-wellbore tortuosity and tip-propagation effects, adding further dimensions of complexity. At the same time they provide facility to adjust their predictions with actual pressure measurements. Whether this multi-adjustment capability leads to better understanding of phenomena is another matter.
The most serious deficiency of most industry models is that they do not provide for optimum fracture performance from a production engineering point of view. They try many "proppant schedules" until one appears the "best". Clearly such ad hoc approach is flawed and statements such as "maximizing conductivity" still torment the industry.
We have a different approach. We use the Unified Fracture Design (UFD) theory to pinpoint the optimum fracture dimensions and then use our p-3D model to allow for the necessary injection. The main benefit of our p-3D approach is to account for constraints, real reservoir configurations and heterogeneity. The use of p-3D models in a design-driven fracture simulation is recommended with the resulting fracture geometry satisfying all elements that other p-3D models can do but, far more important, the geometry thus derived is exactly the one that can maximize well productivity.
