Carbonate_Reservoir_Characterisation

Carbonate Reservoir Characterisations

Rock-Fabric - Classification Integration

• Combines geological rock fabric data with engineering data.

• Components include:

  • Stratigraphy

  • Wireline Logs

  • Geophysics

  • Rock-fabric data

  • Porosity measurements

  • Core analysis studies

  • Diagenesis

  • Permeability

  • Saturation

  • Production pressure

  • Structural analysis

  • Tracer tests

Main Objective

• Purpose is to:

  • Define key geologic parameters for mapping and quantifying carbonate geologic models.

  • Explore the relationship between carbonate rock fabrics and petrophysical properties.

  • Present a generic petrophysical classification of carbonate pore spaces.

Pore Space Terminology and Classification

• Discusses various classifications of carbonate pore types.

• Evaluates Lucia's (1983) classification against Archie’s original (1952) and Choquette and Pray’s fabric selectivity concept (1970).

Abbreviations for Pore-Type Terminology

• Compares pore types used in the report with other classifications:

  • Interparticle (IP) - BP

  • Intergrain (IG)

  • Intercrystal (IX) - BC

  • Vug (VUG)

  • Separate Vug (SV)

  • Moldic (MO) - MO

  • Intraparticle (WP)

  • Intragrain (WG)

  • Intracrystal (WX)

  • Intrafossil (WF)

  • Intragrain microporosity (iguo)

  • Shelter (SH)

  • Touching Vug (TV)

  • Fracture (FR)

  • Solution-enlarged fracture (SF)

  • Cavernous (CV)

  • Breccia (BR)

  • Fenestral (FE)

Petrophysical Classification of Carbonate Porosity

• Emphasizes the petrophysical aspects of carbonate pore space classification.

• Highlights important divisions by:

  • Interparticle porosity (between grains/crystals) and

  • Vuggy porosity (further subdivided into separate and touching vugs).

Classification of Interparticle Pore Space

• Focuses on geological and petrophysical classifications based on:

  • Size and sorting of grains/crystals.

  • Importance of interparticle pore volume in pore-size distribution.

Mercury Displacement Pressure

• Discusses the relationship between mercury displacement pressure and average particle size for nonvuggy carbonate rocks.

Classification of Vuggy Pore Space

• Classifies vuggy pore space based on interconnections, crucial for pore-size distribution characterization.

Separate-Vug Pore Space

• Defined by:

  • Either being within particles or significantly larger than the particle size.

  • Interconnected only through interparticle pore space.

  • Examples include:

    • Intrafossil pore space in gastropods.

    • Fabric-selective separate vugs should be identified for specific fabrics.

Touching-Vug Pore Space

• Defined as:

  • Significantly larger than the particle size.

  • Interconnected pore systems that are substantial in extent.

  • Often showcases nonfabric selectivity in origin.

Rock Fabric/Petrophysical Relationships

• Explores examples of different limestone rock fabrics:

  • Grainstone examples and their variations concerning separate-vug pore space.

  • Effects of pore space on permeability illustrated graphically.

Composite Porosity-Air Permeability Cross Plot

• Shows cross plots comparing nonvuggy limestone and dolostone fabrics with permeability fields.

Permeability Estimation

• Provides transforms between permeability and interparticle porosity for different petrophysical classes:

  • Class 1: Interaction with porosity of 45.35e10^(metric) and permeability based on interparticle ratios.

Continuum of Rock Fabrics and Related Transforms

• Continuum detailed described, showing influences of grain size and sorting on rock-fabric properties across various exercises.

Leverett ‘J’ Function

• Averages capillary pressure data effectively for the classification dimensions described.

Rock-Fabric/Porosity/Water Saturation Relationships

• Presents equations for estimating water saturation across petrophysical class boundaries based on reservoir details.

Summary

• Three classes identified:

  • Class 1: Grainstones and large crystalline dolostones.

  • Class 2: Grain-dominated packstones and medium crystalline dolostones.

  • Class 3: Mud-dominated limestone and fine crystalline dolostones.

  • Each class has generic transformations for permeability and propagates class-specific characteristics.