3. FRACTURE AND MATRIX POROSITY INTERACTION

Fracture Properties Needed

Fracture porosity & permeabilityare both a function of

Fracture Width (e) & Fracture Spacing (D)

Fracture Porosity

Fracture Porosity Magnitude Guidelines for Fracture Porosity -Always Less Than 2% -Excluding Small Zones < 1% -General Less Than 0.5% -Vuggy Fractures 0-Large Fracture porosity is usually low but can be important in specific reservoirs with large vertical and areal extent.

Fracture Porosity is Difficult to Calculateand Even More Difficult to Interpret

While Fracture Porosity is Small in MagnitudeIt is very effective porosityA possible large volume per well due to large drainage area and reservoir thicknessAn assumed high recovery factor

Fracture System Volume as a Functionof Fracture Porosity & DrainageNelson (1985)

2 ftFracture Porosity & ScaleNelson (1985)

Depth & Depletion CorrectionsAre Much More Severe

in Fracture Porosity Than in Matrix Porosity

Fracture & Matrix PorosityCompressibility

Tr Ss from Daw & Others (1974)Fracture & Matrix PermeabilityCompressibility

Fracture Porosity CalculatorNelson (1985)

Fracture Porosity Determinations

Fracture Porosity from Core Analysis

Fracture Porosity vs. Fracture PermeabilityNelson (1985)

K. North SeaChalkValhall FieldFracture Porosity/PermeabilityRelationshipNelson (1985)

Fracture Porosity from OutcropFracture IntensitiesAssumes Fracture Width for Ls at 10,000 ft from Lab MeasurementsNelson (1985)

Sometimes FracturePorosity & MatrixPorosity are Related

PermeabilityFracturePermeabilityDarcy (1856)Lamb (1957)

Fracture System Permeability

Combined Permeability

Fluid Flow in Fractures & Matrix

Flow in Multiple Fracture Sets

Fracture Widths

In Situ Stress & Fracture Closure

kf & km with StressHod Chalk,North SeaConfining Pressure (psi)k (md)Nelson (1985)

Calculated Fracture Width with StressConfining Pressure (psi)e (cm)Nelson (1985)

Fracture & Matrix PorosityCompressibility

Fracture Permeability CalculatorNelson (1985)

% Fracture Permeability PlotNelson (1985)

% Fracture Porosity PlotNelson (1985)

kv vs. kh maxkh 90 vs. kh maxPermeability Anisotropy from Whole-CoreNelson (1985)

Permeability Anisotropy MapRyckman Creek WI # 6Nelson (1985)

kh 90 / kh maxKv / kh maxPermeability Features from Core LogFracturesBedding &FracturesBedding & FracturesStrongB&FFracturesNelson (1985)

Channeled Flow Along a Planar FractureNavajo SsPage Arizona3 ftFracture SurfaceSecondaryCalcite

Interaction Between Fractures & Matrix

Fracture reservoirs are inherently a two porosity system (at least 2)Communication or crossflow can be good, or it can be inhibited by mineralization within or deformation along the fracture planesIt is necessary to document porosity interaction to estimate reserves

PorosityMapOpen FractureNugget Ss, WyomingNelson (1985)

PorosityMapNugget Ss, WyomingSlickensidedFractureNelson (1985)

PorosityMapNugget Ss, WyomingGouge-FilledFractureNelson (1985)

PorosityMapNahanni Fm, NW TerritoriesPartiallyMineralized FractureNelson (1985)

Channeled Flow Along a Planar FractureNavajo SsPage Arizona3 ftFracture SurfaceSecondaryCalcite