| Title | The Nature of Reservoir Fracture Heterogeneity: I - A New Conceptual and Computational Model |
|---|---|
| Authors | Peter C Leary and Peter E Malin |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | fracture heterogeneity, percolation flow, numerical reservoir flow modeling |
| Abstract | The ability to quantitatively model geothermal well connectivity in fracture-heterogeneous reservoirs offers the opportunity to mold field data into physically accurate de facto models of reservoir-scale flow. Heretofore, however, incorporating fractures in reservoir flow models has tended to be mechanically ad hoc and computationally demanding. A large volume of well-log and well-core data points to a physically accurate and computationally tractable basis for simulating fluid flow in fractured reservoirs. Well-log fluctuation power S(k) tends almost universally to scale inversely with spatial frequency k, S(k) ~ 1/k, ~1/km < k < ~105/km. Such power-law scaling may be understood as long-range spatial correlation of in situ grain-scale fracturing of the cemented bonds that characterize most crustal rock. Sequences of porosity  and permeability  from hundreds of meters of clastic reservoir well core tend to obey the fluctuation relation   log() at ~85% +/- 8% cross-correlation level. If porosity fluctuations  in grain-scale fracture density  control permeability fluctuations log() via permeability proportional to grain-scale fracture connectivity factor !, the empirical spatial fluctuation relation is equivalent to the combinatorial identity   log(!). The well-log and well-core reservoir-empirical fluctuation relations for in situ fracture systems can be numerically represented in terms of 2D/3D fracture density fields with model realizations of porosity fluctuations scaled as S(k) ~ 1/k and associated permeability given by   log()). Fracture-borne fluid flow is efficiently computed with finite-element solvers. Grids of dimension 32x64x64 to 64x128x128 can represent broadband in situ fracture heterogeneity to allow rapid quantitative simulation of interwell connectivity systematics. |