Water Resources Research · 1984 · 430 citations · 33 references
EngineeringEarth SciencesGeological EngineeringGroundwater HydrologyReservoir EngineeringSubsurface Fluid FlowDual-porosity FlowDual-porosity ModelingFluid-flow In Porous MediaFracture MechanicsGroundwater FlowWell HydraulicsDual-porosity SystemsFracture Skin EffectsFractured Rock FlowHydraulic GradientsHydraulic Head GradientsMineral Deposition ProcessesPorosityTransient Flow
Theories of flow to a well in a double‑porosity reservoir are extended to include a thin, low‑permeability fracture skin at fracture‑block interfaces, showing that the standard pseudo‑steady‑state model is a special case of this more general theory. The model assumes transient block‑to‑fissure flow with fracture skin that can impede fluid exchange when its conductivity is lower than the matrix, and solves coupled boundary‑value problems for constant‑rate wells in slab‑ and sphere‑shaped blocks in the Laplace domain, accounting for well‑bore storage and skin. The fracture skin reduces spatial variation of hydraulic head gradients within blocks, justifying the neglect of block‑flow divergence in pseudo‑steady‑state models, and numerical inversion yields dimensionless curves that fit well‑test data from the Nevada Test Site fractured volcanic rock.
Theories of flow to a well in a double‐porosity groundwater reservoir are modified to incorporate effects of a thin layer of low‐permeability material or fracture skin that may be present at fracture‐block interfaces as a result of mineral deposition or alteration. The commonly used theory for flow in double‐ porosity formations that is based upon the assumption of pseudo–steady state block‐to‐fissure flow is shown to be a special case of the theory presented in this paper. The latter is based on the assumption of transient block‐to‐fissure flow with fracture skin. Under conditions where fracture skin has a hydraulic conductivity that is less than that of the matrix rock, it may be assumed to impede the interchange of fluid between the fissures and blocks. Resistance to flow at fracture‐block interfaces tends to reduce spatial variation of hydraulic head gradients within the blocks. This provides theoretical justification for neglecting the divergence of flow in the blocks as required by the pseudo–steady state flow model. Coupled boundary value problems for flow to a well discharging at a constant rate were solved in the Laplace domain. Both slab‐shaped and sphere‐shaped blocks were considered, as were effects of well bore storage and well bore skin. Results obtained by numerical inversion were used to construct dimensionless‐type curves that were applied to well test data, for a pumped well and for an observation well, from the fractured volcanic rock terrane of the Nevada Test Site.
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