Unlocking shale gas has been extremely successful during the last decade. Nevertheless, new challenges will continuously arise. One of the most pressing current issues is to know the stimulated reservoir volume (SRV), the part of the reservoir that actually received fracturing fluid. The most widely used technology for estimating SRV is downhole microseismic mapping. Under many conditions, it yields reasonably accurate/reliable information about SRV (Mayerhofer et al. 2008). Unfortunately, it requires an observation well in close proximity to the treatment well in which to place the geophone string used to sense the small seismic signals. This requirement often makes it impossible to provide an SRV estimate for many of the hydraulic-fracture treatments that could benefit from this information.
This paper presents an alternative to the downhole-microseismic SRV mapping. A new method, stimulated reservoir characterization (SRC), is based on surface microdeformation measurements obtained with a precision surface tiltmeter array. Tiltmeter-based hydraulic-fracture diagnostics have been successfully used for more than two decades on more than 10,000 hydraulic-fracture treatments. SRV is typically calculated for highly jointed shale reservoirs or coal seams in which injected fluids can inflate a myriad of interconnected hydraulic fractures in two or more dominant orientations. The measured surface deformation is the superposition of all the deformation fields resulting from the inflation of each individual fracture. This makes the deformation-based approach for SRV estimation a convoluted process and requires much more complex tilt-data analysis than does a simple planar hydraulic fracture. This paper describes a new technique for tilt-based SRV estimation, which is capable of resolving spatial distribution, orientations, and volume percentages of the major components of a fracture network. Hence, the new technique allows not only an insight into the areal penetration of treatment fluids into the reservoir, but also an understanding of how multiple joint sets, each with unique orientations, are actually accepting the injected fluids and proppant. This paper includes synthetic data examples and SRV results derived by applying the new technique to a hydraulic-fracture-stimulation project in the lower Eagle Ford shale formation.