Seismic inversion in the Barnett Shale successfully pinpoints sweet spots to optimize well-bore placement and reduce drilling risks

Abstract

A successful drilling campaign in an unconventional shale play usually brings together disparate pieces of relevant geological, petrophysical, and geophysical information to build a realistic and accurate model of the subsurface. Including seismic inversion information in the knowledge mix promises to be a gamechanger because it can pinpoint sweet spots in the play, even with sparse well control. The sweet spots should have all of the ingredients to make wells profitable -good free gas volumes, good poro permeability, and brittleness (hence fracable). If the rock interval exceeds a threshold of brittleness, its fracability can be reliably estimated by the combination of Poisson's Ratio and Young's Modulus. These two mechanical properties are combined (Rickman et al, 2008) to indicate the rock's propensity to fail under stress (Poisson's Ratio) and to maintain a fracture (Young's Modulus). In this Barnett Shale project, a simultaneous AVO inversion was used to demonstrate the feasibility of constructing a subsurface geological and geomechanical model describing the thickness and complex architecture of the brittle/fracable formation portion. This information can, in turn, be used to determine the optimal well bore trajectory. Considering that the Barnett Shale has a significant structural component, an accurate design of the well bore trajectory is required to remain within the bounds of the most appropriate facies. The ultimate result of strategic well bore placement is the maximization of cumulative volumes of hydrocarbon production per barrel of frac fluid.Historical data show that productivity is a function of the induced fracture extent and how well the formation can maintain those fractures. Fracability, the propensity of the formation to fracture and maintain the fracture, is directly correlated with brittleness. In turn, the field results validate that the formation's susceptibility to fracturing can be reliably predicted from the brittleness as calculated using Poisson's Ratio and Young's Modulus (Pitcher and Buller, 2012).

Quantification of potential macroseismic effects of the induced seismicity that might result from hydraulic fracturing for shale gas exploitation in the UK

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