Lecture Notes: Formation Evaluation in Petroleum Engineering

Introduction

• Lecturer: Mustafa Orby, Graduate Program Director and Professor of Petroleum Engineering at the American University in Cairo
• Background: 25 years in the industry, now sharing experience with academia
• Focus of Lecture: Formation evaluation beyond tool usage (previously covered)

Formation Evaluation Overview

• Types of Analysis: Quick Look vs. Complex Well Analysis
  • Quick Look: Immediate decisions (e.g., continue completing a zone)
  • Complex Analysis: In-depth post-drilling evaluations in the office
• Tools for Formation Evaluation
  • Wireline Logging Data (post-drilling)
  • Basic tools: Borehole caliper, Gamma ray, Neutron, Density, Resistivity
  • Triple Combo: Neutron, Density, Resistivity (plus Gamma ray and Caliper)

Basic Wireline Logging Tools

1. Borehole Caliper
   • Measures borehole diameter at different depths
   • Important for understanding borehole conditions
2. Gamma Ray Tool
   • Measures total gamma ray activity of the rock
   • Identifies lithology
3. Neutron Tool
   • Measures hydrogen concentration
   • Used to find porosity
4. Density Tool
   • Measures rock density
   • Combined with neutron tool for lithology and porosity analysis
5. Resistivity Tool
   • Measures fluid saturation (water vs. hydrocarbon)

Formation Evaluation Workflow

1. Environmental Correction (Data Quality Control)
   • Borehole size correction
   • Mud weight correction
   • Salinity correction
   • Mud additives correction
   • Temperature and pressure correction
2. Porosity and Lithology Calculation
   • Calculate Clay Volume: Using gamma ray data
   • Calculate Density Porosity: Formula-based on density measurements
   • Average Neutron and Density Porosity: Cross plot porosity calculation
   • Effective Porosity: Corrected for clay volume
3. Fluid Saturation Calculation
   • Water saturation (Sw) and Hydrocarbon saturation (Sh) using Archie's equation
   • Visual lithology determination

Visual Lithology Determination

• Gamma Ray Response: High for clay, low for anhydrite and salt
• Neutron and Density Response: Key Indicators
  • Clay: Neutron to the left, density to the right, high gamma ray
  • Sandstone: Density to the left, neutron to the right, lower gamma ray
  • Limestone: Neutron and density overlay
  • Dolomite: Similar separation to clay but low gamma ray
• Effective Porosity: Influenced by clay content; critical for decision-making

Example Workflow Application

1. Load Data into Software: Environmental correction using software tools
2. Identify Logging Company: Knowing the company helps apply specific corrections
3. Apply Environmental Correction: Specific corrections for gamma ray, density, neutron, etc.
4. Visual Lithology Identification: Identify clay, sandstone, limestone, dolomite through log responses
5. Calculate Clay Volume: Using gamma ray minimum and maximum readings
6. Calculate Porosity: Density porosity, average neutron and density porosity, and effective porosity
7. Calculate Fluid Saturation: Using Archie's equation for quick decision-making

Summary

• Quick Look Well Evaluation: Steps include environmental corrections, visual lithology determination, calculation of clay volume, porosity, and fluid saturation
• Importance: Enables quick decisions on well completion and potential zones

Q&A Highlights

• Density Log in Cased Sections: Not reliable; density measurements are for open-hole analysis
• Geological Complexity of Gulf of Suez: High complexity requires skillful evaluation
• Identifying Hydrocarbon Zones: Use effective porosity and Archie's equation for quick look analysis
• Mechanical Errors in Logging Tools: Trained field engineer can detect errors
• Availability of Slides: Not provided, webinar recording is the resource

End of Lecture Notes