Studies in Naturally Fractured Reservoirs for Improved EOR...Contribution to EOR in Wyoming •...
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Studies in Naturally Fractured Reservoirs for Improved EOR Scott P. Cooper John C. Lorenz
Transcript of Studies in Naturally Fractured Reservoirs for Improved EOR...Contribution to EOR in Wyoming •...
Studies in Naturally Fractured Reservoirs for Improved EOR
Scott P. CooperJohn C. Lorenz
Outline
1) Brief discussion on natural fractures2) Natural fractures associated with
anticlines
Acknowledgements: EORI, collaborators within EORI, Landowners
Who cares?
1. Natural Fractures
Why we care• Fractures enhance permeability and introduce a
direction of maximum and minimum permeability. Thus, fractures can be viewed as a subsurface plumbing system.
• Fractured reservoirs are not isotropic, and models of fluid movement must account for such heterogeneity.
• Directional permeability has important applications to draw-down and/or injection with regard to well placement, and EOR.
kk
Isotropic and Anisotropic Drainage Areas
kmin
kmax
kmin
kmaxkmin
kmax
kmin
kmax(Harstad, 1998)
1. Fractures are not simple. -Populations are spectra-Many fracture types-Different effects on reservoirs
2. Vary by lithology, stress regime3. Enhance or degrade reservoirs4. Permeability is dynamic
“Fracture” is a basket term
Extension Fractures• Most common, Simplest• Typically vertical• Form by opening against the minimum stress • Motion normal to the fracture walls
Evenly spaced, bed-normal extension fractures in sandstone
Shear Fractures• Fracture walls are
offset • Faults vs. fractures• Commonly as
conjugate pairs– Strike-slip, normal
dip-slip, reverse dip-slip
• Horizontal shear fractures
σ1
σ2
σ3
Normal
Strike-slipσ1
σ2
Reverseσ1 σ2
σ3
Dip-slip conjugate shear fracture set in sandstone
Mineralization and Dissolution
• Quartz, calcite, clay, barite, hydrocarbon, etc.
• Multiple phases are common• Complete or partial fill, often in the same
fracture• Dissolution provides enhanced
permeability and connectivity
Calcite crystals cover a fracture face, Mesaverde Fm., Colorado
Slot permeability along a dissolved fracture
1/2 mile
Over 132 miles of mapped dissolution passageways
Wind Cave, South Dakota
N
2. Natural Fractures associated with Anticlines
1) Highlight three outcrop studies of fracture origins, characteristics, and distributions at Teapot Dome, Flat Top and Beer Mug anticlines as part of a spectra
2) Subsurface studies of fracture characteristics, distributions, and effects at East Salt Creek, Alcova, Hatfield, Mahoney, Rangely, Zeisman and several other reservoirs around the state
A thorough understanding of fractures (including type and distribution) across this spectra will allow operators to place wells in optimum positions and design EOR programs that will maximize EOR efficiency
Flat Top-Teapot-East Salt Creek-Alcova-Hatfield-Beer MugIntensity of folding/deformation
Spectra of Anticlines
Teapot Dome
Conjugate Normal Faults and Fractures
Fold Hinge
Hinge-parallel
Hinge-perpendicular
Hinge-oblique
NN
Cooper, S. P., Goodwin, L. B., and Lorenz, J. C., 2006, Fracture and fault patterns associated with basement-cored anticlines: The Example of Teapot Dome, Wyoming, American Association of Petroleum Geologists Bulletin, v. 90, n.12, p. 1903-1920.
Plan view of conceptual model of permeability domains related to intersecting or relatively nonintersecting fracture patterns along a Teapot Dome-type anticline.
Potential drainage ellipses are shown outside the anticline. Areas of nonintersecting fractures show drainage ellipses that parallel the fracture orientations. Areas with numerous intersections should have near circular drainage patterns.
Flat Top anticline
Early fractures
basement
-F1 fractures form before folding, parallel to the max horizontal compression that initiates thrusting and folding: hinge normal
F1
• Later fractures: bending
Later Fractures
-F2 fractures form during folding due to flexure: hinge parallel
F1
F2
Thin-bedded sandstone
Average spacing 0.7 m. Bed thickness 1.2 m.
Thrust translation was oblique to the thrust front
1 mi/1.6 km
N
Blevins, 1984
10 km/6 mi
N
Medicine Bow
• Later fractures: bending
Later Fractures
-F2 fractures form during folding due to flexure: hinge parallel
F1
F2
Minimal facies variations in fracturing, backlimb
Cross-bedded
Flat-bedded
50 m
Beer Mug anticline
3
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Dr. Peigui Yin
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Linear Scaling
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Complicated yes but …
• We are reviewing a spectra of anticlines
• To develop predictive capabilities and models
• To be used as tools for EOR
SummaryContribution to EOR in Wyoming
• Natural fractures dominate fluid flow in Tensleep reservoirs and are therefore a dominant control on the recovery of oil from the subsurface.
• A thorough understanding of fracture characteristics and distributions will allow operators to place wells in the optimum positions and design EOR programs that will maximize EOR efficiency.
• An understanding of the origins of the fractures will provide a basis for predicting fracture characteristics and distributions between wells, and thus their effects on flow for various EOR techniques.
Thank You
Projects• Outcrop studies
– Flat Top Anticline study– Alcova Sand Creek/Casper SS– Beer Mug Anticline– Sand Creek/Casper outcrop study (with Mark Tomasso)
• Subsurface study– Hatfield core– Mahoney Dome– Teapot Tensleep– East Salt Creek studies– Minnelusa studies
• Fractures class Jackson Hole, Feb 2009
Tensleep Natural Fractures Project
1) an assessment of the published literature on outcrop and subsurface natural fractures in the Tensleep Sandstones, as well as their effects on oil production
2) outcrop studies of fracture origins, characteristics, and distributions at Flat Top and Beer Mug anticline
3) subsurface studies of fracture characteristics, distributions, and effects at Hatfield Dome, Mahoney Dome, and several other reservoirs around the state
• Fractures are the plumbing system.
• Fractures enhance permeability and introduce a direction of maximum and minimum permeability.
• Directional permeability has important applications to draw-down and/or injection.
• Fractured reservoirs are not isotropic, and models of fluid movement must account for this heterogeneity.
Summary
Deformation Bands
• Shear fractures– Minimal shear
• Form in poorly-cemented, high-porosity sands– The sand often becomes well cemented later
0 1mm
Best applied to thin-skinned thrusts
Best applied to basement-involved thrusts
σ3
σ3
σ1σ1
σ1
σ3
σ1
σ3
10 km/6 mi
N
Medicine Bow
Complicated yes but …
• We are reviewing a spectra of anticlines• To develop predictive capabilities and
models• To be used as tools for EOR
Thank You
Slot permeability along a dissolved fracture
