Unconventional resources such as shale gas are becoming increasingly important exploration, development, and production targets. The variation in well performance observed between various shale reservoirs and indeed within individual basins and on individual pads, has served to dispel the myths regarding the perceived homogeneity of shale gas targets. With increased quantities of geological and engineering data and more quantitative and deterministic analyses, it is now clear that in order to ensure the economic success of shale gas production we must understand the microscopic and mesoscale heterogeneity of the shale reservoirs. This can be advanced through interdisciplinary studies that incorporate traditional and advanced geophysical data and methods with geological understanding and engineering measurements. This understanding is critical in field development, optimizing well placement, well spacing and length of horizontal wells, and the hydraulic fracturing effort needed to maximize recovery. Some of the key parameters are total organic content and porosity that control the resource density estimation, and geomechanical properties that are related to the rock’s mechanical strength. These parameters and their lateral distributions are needed for areal and interval selection in order to optimize stimulation programs.
- Mapping natural faults/fractures – We want to know the spatial distribution, the scale (micro or macro), the density, and the relationship to the stress field.
- Identifying “fraccable” intervals that can be easily fractured – We want to know the brittleness, the fraccability in terms of geomechanical properties, such as Young’s modulus, Poisson’s ratio, and stress field.
- Monitoring of hydraulic fractures – We want to know the length, height, and shape of the fractures.
This is also true for other types of unconventional resources such as tight sand and tight oil. Geophysics plays the key role in addressing all these “fracture” issues. So there are abundant opportunities to apply geophysical tools to characterize unconventional resources.