Natural Fractures; Their Role in Resource Plays - Tight Oil From Shale Plays World Congress 2011
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Tight Oil From Shale Plays
World Congress 2011
January 31st & February 1st , 2011 Denver, CO
Natural Fractures;
Their Role in Resource Plays
By
Hutch Jobe
SM Energy
Evolution of the Resource Play
1970’s 1990’s 2010’s
Tight Gas Sands (TGS) CBM become vogue
Confined to deep basin areas Realization of sorbed & absorbed gas Resource play targets not litho-
Recognize no distinct LKG Recognition of coal composition dependent
Recognized perm as a driver Fractures and cavitation in coals
Recognized pervasive Sw Dewatering concept Brittleness, TOC, natural fractures are key
Unconventional pay concept born Pattern & high density drilling
Antrim & Barnett Shale play emerge Designer frac’s optimize induced fractures
Image logging is greatly enhanced
Source and carrier bed relationships
Sequence stratigraphic framework
1980’s 2000’s Aggregate development drilling
TGS plays expanded/evolved Shale Resource Plays explode Surface array/Buried array micro-seismic
Recognition of over pressuring Source rocks become reservoirs
Basin Center Gas concept Horizontal drilling becomes an art form
Tight Gas tax credits Horizontal logging and frac’ing evolve Simal-fracs and Zipper-fracs
Improvements in 2D and 3D Multi-stage completions
Role of natural fractures emerges 3D is a “must” Go horizontal in produced TGS fields
Micro-Seismic becomes very popular
Natural fractures are key to perm Vertical drilling phases out to horizontal
Shale oil and oil resource play focus
Misconceptions about Resource Plays
They are all shales; you stimulate them all the same;
stimulation of the matrix makes the play; and they should all
produce the same.
The prospective Resource Play is an unconventional
reservoir.
Since nothing shows up on seismic, the reservoir is not
fractured; we drill in “quiet areas” where no faulting is
present.
What is the definition of a Shale?
Grain Size and Bedding are the controlling factors defining a Shale
Bedding Thickness
.0625 mm .0039 mm < .0039 mm
(1/16 inch) (1/256 inch)
Grain Size
(Modified Rose & Assoc.; from Levine, 2003)
Thinly Laminated Shales Interbedded with
Siliceous Layers; Woodford Shale
Lithologies of High Profile Resource Plays
Closest to a Shale Closest to a Limestone Closest to a Siltstone Closest to a Dolomite
Barnett Eagle Ford Haynesville (“stack”) Bakken
Woodford Niobrara Montney Three Forks
Fayetteville Mancos Collingwood
Marcellus Bossier?? (Utica)
SWS?? SWS??
Muskwa
Conasauga
Huron
New Albany
Antrim
Bossier??
Closest to a Clastic/Congl
Granite Wash
A Statement from Experience
All reservoirs have some component of
natural fracturing which contributes to the
permeability within the rock
What is a Natural Fracture?
---”discontinuity caused by brittle failure” (Narr etal, 2006); a compromise of the
structural fabric in rock caused by stress (tectonic, HC, and impact generated)
---a fracture can be a crack, joint, fault, deformation band or vein, and
predominantly perpendicular to bedding
---a fracture is a function of scale; some may have displacement, some may have
have shear, but all impact the ability for fluid flow; transmissibility; permeability
The Role of Fracturing on Permeability Upon
Compaction in Sandstones
Fracturing therefore is beneficial for flow in Tight Gas Sands; natural and induced
How Do We Describe Natural Fracturing?
Via Fracture Intensity>>>length, height, density, spacing, aperture,
patterns, bed thickness, rock composition;
relationships with curvature, structure, dip
and faulting; it’s 3-dimensional
(Hennings, 2006)
Understand the difference between closed/healed fractures
versus cemented fractures
Closed fractures on a surface do not imply they are closed
throughout the volume, cemented fractures canKey Drivers to Resource Play Performance
Know the Structural History; Understand Natural Fractures
Know the Rock; Sequence Stratigraphic Framework
Brittleness: Understand Rock Properties
TOC Content; % Percent by Weight, Kerogen Type
(richness), and Maturity ( Ro--heat)
3D Seismic and Micro-seismic; Fault Geometries, Fault
Magnitudes, SRV
Stimulation ProceduresStructural Setting Determines Natural
Fracture Geometry
Drape over Enhancement via
structural highs structural closure
Dip-slip & Strike-slip
faulting generate fracturing
*Natural fractures can help
determine productive limits
(Modified Rose & Assoc.; Steward, 2009)
associated with Resource Plays*Silo Field Isocum Map: Fractured Niobrara
0 to 50 MBO 100 to 150 MBO >200 MBO
12 wells have produced between
50 to 100 MBO 150 to 200 MBO 200 MBO to 481 MBO
*Data comes from 114 producers; Swanson mean of 74 MBO; range is .3 to 481 MBO*Silo Field Isocum Map: Fractured Niobrara
0 to 50 MBO 100 to 150 MBO >200 MBO
12 wells have produced between
50 to 100 MBO 150 to 200 MBO 200 MBO to 481 MBO
*Data comes from 114 producers; Swanson mean of 74 MBO; range is .3 to 481 MBO*Sequence Stratigraphic Framework Helps
Define the Resource Target
Off lap sands and
washes
(modified)
Key attributes: position of the margin, geometry of margin, angle of slope,
fauna diversity optimizes TOC, water depth governs TOC, water depth
governs faciesRock Properties ---Brittleness; the ability for rock to fracture naturally or fracture via stimulation; it can be proportional to permeability and stimulation enhancement ---Brittleness and elasticity is a function of lithology/composition ---Siliceous and dolomitic rocks tend to be more brittle than limestones and clay rich rocks; clay in rock correlates to more ductility
Thermal Maturation Windows for
Various Resource Plays
Eagle Ford
Marcellus
TOC % (modified: Bustin etal, 2008)Kerogen Types and Their Link to Ro,
Tmax, HC Phase, and HC Efficiency
Lacustrine, Marine, Terrestrial,
Oil Prone Oil Prone Gas Prone
(After Rose & Assoc,; Modified Jarvie, 2009)In Source Rock Resource Plays; Understanding Relationships Between
Fracturing Caused by Hydrocarbon Generation, Maturation, and Kerogen
Type Can be Important
(unpublished, MacKay, 2010)
Thermal maturation of organic material can affect fluid type in terms of molecule
size and compressibility (this can influence the areal extent of the pressure event)Micro-Seismic has Evolved into an Important
Part of Resource Play Development
---Down-hole monitor approach: initial application; monitor well can be
expensive or difficult to position; data is usually good from a vertical aspect;
fair to good lateral data
---Surface array approach: gaining popularity; no monitor well is needed;
reasonable expense; vertical resolution not as good as down hole; lateral data
is good; additional permitting and preparation
---Buried array approach: gaining popularity; no monitor well is needed; fairly
expensive but can be used multiple times; vertical resolution similar to the
surface array; lateral data is good; usually covers the largest area; additional
permitting and preparation
(Bennett etal Oilfield Review, 2006)Depiction of Surface Array Design
---Vertical well case
---Horizontal well case
---Each radius approx. equal to
---Survey has an ellipse shape due
depth of target
to lateral wellbore length
---Multiple geophones per radius
---Multiple geophones per radius
(Duncan & Laking, 2006)Depiction of Buried Array Design
---Spacing of stations is a func. of
budget, development plan,
signal to noise, etc.
---Depth of stations can vary but
100’ to 300’ foot is common
---Multiple geophones are hung in
each station
(MicroSeismic, 2010)Map View & Cross Profile of Micro-Seismic Data
Gaps in events suggest Varying vertical growth
poor stimulation coverage; of events suggests fracs
and the possible need for might not be confined to
more stages target interval
(Modified; MicroSeismic Website, 2010)Surface Array Micro-Seismic Application
**Damage zones associated with faulting
can be detrimental during stimulation**Map View of Events Associated with “Relax-a-Frac” Periods
Cross-Sectional View of Total Events During Stage Zone of Interest
Final Distribution of Events Throughout Lateral
Learning's and Value of Micro Seismic
---Helps confirm in-zone stimulation
---Helps define lateral extents of stimulation
---Can calculate a stimulated rock volume (SRV)
---Identify fracture orientation
---Identify faulting
---Identify “thief” zones during stimulation
---Confirm spacing of frac stages along the length of the lateral
---Confirm conductivity intensity of frac fluids and design
---Helps identify well spacing, unstim. SRV, and potential recompl.
Potential Re-fracs
or new drill areas
(Pinnacle Technologies Website, 2010)How Can Geo-Science Effect Stimulation Design?
---Accurate lithology/composition determines most effective frac design:
a.) high clay content>>>more gel design
b.) low clay content>>>more slick-water design
c.) more brittle rock might not need as high a rate
d.) elasticity of rock might give insight on pump procedures
---Natural fracture and fault knowledge effects:
a.) well placement
b.) stage periodicity along lateral (length and spacing)
c.) propant size, volume, and timing
d.) SRV aerial size and distribution
---3D Seismic and Micro-Seismic gives confidence to:
a.) did we stay in zone
b.) are we too close to a fault
c.) did we land in the correct spot
d.) does the target extend this far or in this direction
---Understanding the rocks direct us to which resource plays we should
pursue and which one’s we should avoidIn the past, we were concerned with the trap
at the end of a hydrocarbon migration event.
Now we are concerned with the pathway of
the entire migration process.You can also read
