Lecture Notes: Reservoir Characterization - Carbonates

Introduction

• Moderator: Shahad Behjit, third-year petroleum engineering student at K&U, Kurdistan, Iraq.
• Speaker: Dr. Mustafa Archi, Ph.D. from North Carolina State University, 25 years in the petroleum industry.
• Session focus: Carbonates in reservoir characterization, differences from plastics.
• Important aspects: Deposition, porosity, lithology, saturation.

Key Differences Between Carbonates and Plastics

• Carbonates: Complex grain/crystal structure, secondary porosity (fractures), variability in evaluation.
• Plastics: Simpler, primarily grain-focused, less variability.

Importance of Porosity Structure in Carbonates

• Porosity structure crucial for understanding reservoir properties: depositional environment, water saturation.
• Archie’s initial models, progressed by others like Lucia.
• Different porosity types affect fluid saturation and permeability.

Gamma Ray in Carbonates

• **Gamma Ray Tool Types: **
  • Total Gamma Ray: Measures total gamma rays without distinguishing sources.
  • Spectral Gamma Ray: Differentiates between potassium, thorium, and uranium.
• **Role of Gamma Ray in Carbonates: **
  • More significant compared to plastics.
  • Helps identify rock types and fabrics.
• **Gamma Ray and Fabric Identification: **
  • Differentiates grain-dominated vs. mud-dominated structures.
  • Mudstone, whackstone, packstone, grainstone, limestone, dolostone.

Rock Fabric and Classification

• **Carbonate Structures: ** Limestone (grain), dolostone (crystal), grain-dominated or mud-dominated.
• **Types: ** Grainstone, Packstone, Whackstone, Mudstone, Crystal sizes (dolostone).
• **Evaluation: ** Mud logs describe carbonate rocks, emphasizing fabric and grain/crystal dominance.

Lucia’s Contributions

• Lucia’s models significant in carbonate evaluation: porosity, permeability, and saturation.
• Petrophysical properties linked with rock fabric: Interparticle (grains/crystals) and secondary porosity (bugs/fractures).
• **Classifications: ** Classes based on grain size, structure, and how these affect permeability.
• **Examples: ** Different classes (1, 2, 3) used to calculate porosity and permeability.

Water Saturation in Carbonates

• Complicated, not as straightforward as in plastics.
• Relationship between porosity and height above free water level (H_e).
• Example provided using Lucia's model vs. Archie's method.

Conclusion

• Gamma ray and spectral gamma ray play a crucial role in carbonate Evaluation.
• Understanding rock fabric and structure is essential for accurate reservoir characterization.
• Future session: Q&A on porosity in gas reservoirs, salt sections, and anhydrite sections.

Q&A Highlights

1. Neural Networks: Complex topic, needs dedicated webinars to cover comprehensively.
2. Sequence Stratigraphy: Applies to carbonates, linked with rock fabrics and deposition environments.
3. Types of Limestone: Misconception that production is exclusively from dolomite; important to know limestone types as well.