ABSTRACT
The development of unconventional resources, whether shale gas and oil or tight gas and oil, involves the challenge of producing hydrocarbons from formations with very low porosities and permeabilities. The absence of a significant natural permeability in unconventional resources has economic consequences that affect the method by which these resources are assessed and developed. Conventional field development relies upon both well production tools and dynamic reservoir models to estimate the production from wells of specific geometries. The estimates are based on pressures, fluid properties, matrix or gross permeabilities, as well as the porosity, water saturations, relative permeabilities and net to gross lithology estimations of the formation. These reservoir models are used to predict the expected production profile for wells, the plateau production, and production decline for specific development scenarios. The well production forecasts are, in turn, used to generate revenue projections that are used in the field development economics to evaluate the project attractiveness and viability.
In sharp contrast, the development of unconventional resources in practice is less reliant on well production models and dynamic reservoir models. Production from these tight formations relies not only upon Darcy flow but also on diffusion and desorption from the matrix and two-phase flow along the fractures as detailed in Chapter 11 and Chapter 14. Models with this additional complexity are not well developed, and much of the required input data (such as the desorption isotherms, and the hydraulic fracture and natural fracture geometries and conductivities) are absent during the early development stages.
