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Different Rock Types … Mechanical Behavior and Engineering ...€¦ · North of Fort McMurray,...

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© M B D C I © M B D C I 5-A Different Rock Types Different Rock Types Different Rock Types Mechanical Behavior and Engineering Mechanical Behavior and Engineering Challenges Challenges Maurice Dusseault
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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


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