PETE311_06A_Class05_(Maggard)

PETE311_06A_Class05_ - COMPRESSIBILITY OF RESERVOIR ROCKS COMPACTION OF SEDIMENTS Porosity is reduced by compaction Porosity reduction is

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COMPRESSIBILITY OF RESERVOIR ROCKS
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• Porosity is reduced by compaction – Porosity reduction is determined by maximum burial depth – Principal effects are: • Changes in packing • Pressure solution • Recrystallization • Deformation of rock fragments • Compaction effects are not reversed by erosional unroofing (hysteresis effect) COMPACTION OF SEDIMENTS
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MECHANICS OF COMPACTION Modified from Jonas and McBride, 1977 Platy Grains (e.g., clays) Non-Platy Grains (e.g., qtz., feldspar) Rotation and Closer Packing Ductile Grain Deformation Breakage of Brittle Grains Pressure Solution At Grain Contacts Ductile Framework Grain, e.g., Shale Rock Fragment)
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Relationship of Original Formation Porosity to Overburden Pressure 50 Overburden pressure, psi P o ro s i t y , % 30 40 20 10 0 0 1,000 3,000 2,000 4,000 5,000 6,000 Sandstones Shales
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Isothermal Compressibility • General Definition – The relative volume change of matter per unit pressure change under conditions of constant temperature • Usually, petroleum reservoirs can be considered isothermal (an exception: thermal stimulation) • Increasing pressure causes volume of material to decrease (compression) - e.g. reservoir fluids • Decreasing pressure causes volume of material to increase (expansion) - e.g. reservoir fluids
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Isothermal Compressibility • General Equation – C: Coefficient of Isothermal Compressibility • ALWAYS positive value • oilfield units: 1/psia – V: Volume • oilfield units: ft 3 – p: Pressure exerted on material • oilfield units: psia – Negative sign in equation determined by V/ p term, to force the coefficient C to be positive
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This note was uploaded on 12/03/2009 for the course PETE 311 taught by Professor Staff during the Spring '08 term at Texas A&M.

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PETE311_06A_Class05_ - COMPRESSIBILITY OF RESERVOIR ROCKS COMPACTION OF SEDIMENTS Porosity is reduced by compaction Porosity reduction is

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