ROCK PROPERTIES

ROCK PROPERTIES

1. RESERVOIR

   • porous geological formation
   • pore space water+HC
   • eg: limestone, sandstone, dolomite
   • behavior determined by
     • gravitational force (density)
     • capillary force (fluid climb up surface)
   • requires a porous media

2. Tests

   • routine core analysis
     • Poro, Permea, saturation
   • special tests
     • press, wettability,tension

3. POROSITY

   • ratio of pore space:bulk volume
     • good reser. :15-20% poro. Poor: 5-10%
   • Types
     • Primary (deposition)
     • Secondary (changes: faults, fracture, cement)
   • Cal.
     • HC porosity
     • Total/absolute poro
     • Effective Poro
       • only inter-connected pore (not incl. trapped pore)
   • Influenced by
     • large grain size/shape/ narrow dist. (same size grains) (inc.)
     • sorting & angularity packing (inc.)
     • compaction (press, depth) decre.
     • chemical sol (decrease), fracturing (inc.)
   • Measured by
     • core scale
       • effective poro: fluid inject, extract mass
       • weight method
       • Helium Porosimeter (press)
     • log
       • >difficult,$$$, usually run to measure many properties at once
     • Production performance
       • data from reser. production over years
   • define rock ability to store fluid, void fraction
   • produce ISO-POROSITY map of reser.

4. CONSOLIDATED (lose grain) vs. UNCONSOLIDATED (cement/chemical stick rock together)

   • Gravel, sand, silt, clay vs. basalt, shale, lime/sandstone

5. FLUID SATURATION

   • fraction of pore vol. occupied by that fluid
   • during production S(oil/gas) decr., S(water) inc.

6. PEMEABILITY - HYDRAULIC CONDUCTIVITY

   • absolute permea
     • capacity to transport fluid through pores
     • large regular grains (decr. SA, friction) inc. pemea
     • exist of another phase, clay/cement form. decr. pemea
     • fracture readily incr. pemea
     • KLINKENBERG effect variate pemea
   • CONVENTIONAL (sandstone->gravel)
   • UNCONVENTIONAL (shale)
   • PARAMETERS
     • Average velocity (discharge Q)
     • Interstitial velocity (linear v or pore v)
     • Hydraulic gradient: ratio change height:length of sand pack
     • Potential gradient: ratio change poro: length of sand pack
   • measured by: Core flood test (inject fluid), well test (cal. from flow, press)

7. a rock property independent of position within porous medium

   • HOMOGENOUS medium

8. a rock property independent of direction within porous medium

   • ISOTROPIC medium

9. a rock property vary at a point of porous medium

   • ANISOTROPIC medium

10. COMPRESSIBILITY

    • change in vol. (rock, pore, fluid) in press
    • during production: press decr.- rock bulk vol. decr.- grains expand -pore vol. decr. (poro)
    • Formation compressibility
      • equal to pore compressibility

11. RESISTIVITY

    • electrical properties
    • depend on void, fluid type, salinity, temp, poro, pore geometry, form. stress, rock composition