different rock types … mechanical behavior and engineering ...€¦ · north of fort mcmurray,...
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Different Rock TypesDifferent Rock Types……Mechanical Behavior and Engineering Mechanical Behavior and Engineering
ChallengesChallenges
Maurice Dusseault
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Lithotypes Lithotypes –– Rock TypesRock Types
� (Igneous – metamorphic) –sedimentary� Clastics (particulate deposition)
�Sandstones (friable, competent, fractured…)
�Shales (smectitic – quartz-illite – others)
�Carbonates (shell beds, oolites…)
�Coal, diatomite, North Sea Chalk
� Chemical or Precipitates�Halite + associated strange minerals (bischofite)
�Gypsum (shallow) and anhydrite (deep)
�Carbonates (precipitates)
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Sandstone Sandstone –– Weak SandstonesWeak Sandstones
σ′ 3
σ′1
σ′σ′σ′σ′n
ττττ
φφφφ = 30% in situ, 35% in the core labdamage
Shaley zone, sheared
Oil sand, intact
σ′a
σ′r
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Sandstone DiagenesisSandstone Diagenesis
� Dense grain packing
� Many long contacts
� Concavo-convex grain contacts
� SiO2 precipitated in interstitial regions
� Only 1% solution at contacts = 8% loss in volume
� -A stable interpenetrative fabric, high stiffness
Fine-grained unconsolidated
sandstone
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Dense but Permeable QuartziteDense but Permeable Quartzite
Xal overgrowths, interpenetrative structure!
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70 m of Athabasca Oilsands, φ = 30%, So = 0.8, µ > 1,000,000 cP
North of Fort McMurray, Alta
Reservoirs are heterogeneous & aniso-tropic at all scales (microns to kilometers)
…UNCERTAINTY…
Even sandstone reservoirs show a great variability, especially vertically, and properties can change over distances as small as a few millimeters. Clearly, simplifications are needed for analysis.
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Conglomerates are ClasticsConglomerates are Clastics……
But, the grain size is larger. A problem for testing, but in the
reservoir a pebble or a 100 micron grain are the same (in a sense).
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This is a Sandstone with CoalThis is a Sandstone with Coal……
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specimen
∆σ′v
εh
= 0
εh
= 0
Unusual Materials (Diatomite)Unusual Materials (Diatomite)……
SPE75230, Barenblatt et al, 2002
Diatomites are formed from the skeletons and spicules of Diatoms. They are
“collapsing” materials.
Source: Bruno and Bovberg, 1992
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Grosmont Formation, AlbertaGrosmont Formation, Alberta
Courtesy : Alberta Geological Survey via Dr. Jose Alvarez
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Are Fractures Open or Closed?Are Fractures Open or Closed?
Sou
rce:
N. B
arto
n an
d A
. Mak
urat
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Heterogeneous EvaporitesHeterogeneous Evaporites
Original specimen - Post-test appearance
Salts and anhydrites are not reservoir rocks, but they are seals, or else containment rocks for gas storage (salt). Also, we have to
drill through 500 – 2000 m of salt occasionally!
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Different Rock TypesDifferent Rock Types……
� Different characteristics – stiff→soft, strong→weak, permeable→impermeable, etc…
� Different stratigraphic sequences in the ground (salt domes, clastic interbeds, evaporates, etc.)
� Different responses to factors such as depletion, EOR, thermal processes
� Different chemical interactions (shale, salt)
� Knowledge of different lithotypes allows us to develop a general picture of what to expect…
� …leading to better engineering, interpretation