Hydraulic fracturing is an economically important stimulation technique applied to reservoirs to increase oil and gas production. During hydraulic fracturing stimulation process, highly pressurized fluids are injected into a reservoir rock. Fractures are created when the pressurized fluids overcome the breaking strength of the rock (i.e., fluid pressure exceeds in-situ stress). These induced fractures and fracture systems (network of fractures) can act as pathways through which oil and natural gas migrate en route to a borehole and eventually brought up to surface. Efficiently and accurately characterizing created fracture systems is important to more fully realize the economic benefits of hydraulic fracturing. Determination and evaluation of hydraulic fracture geometry can influence field development practices in a number of important ways such as, but not limited to, well spacing/placement design, infill well drilling and timing, and completion design.
More recently, fracturing of shale from horizontal wells to produce gas has become increasingly important. Horizontal wellbore may be formed to reach desired regions of a formation not readily accessible. When hydraulically fracturing horizontal wells, multiple stages (in some cases dozens of stages) of fracturing can occur in a single well. These fracture stages are implemented in a single well bore to increase production levels and provide effective drainage. In many cases, there can also be multiple wells per location.
There are several conventional techniques (e.g., microseismic imaging) for characterizing geometry, location, and complexity of hydraulic fractures out in the field. As an indirect method, microseismic imaging technique can suffer from a number of issues which limit its effectiveness. While microseismic imaging can capture shear failure of natural fractures activated during well stimulation, it is typically less effective at capturing tensile opening of hydraulic fractures itself. Moreover, there is considerable debate on interpretations of microseismic events and how they relate to hydraulic fractures. Other conventional techniques include solving geometry of fractures as an inverse problem. This approach utilizes defined geometrical patterns and varies certain parameters until numerically-simulated production values matches field data. In practice, the multiplicity of parameters involved combined with idealized geometries can result in non-unique solutions.