Well Logging Course Quiz - 2nd Semester

Well Logging Course

• Course Title: Well Logging
• Course Code: G 401
• Academic Level: Fourth Year
• Credit Hours: 3 hours/week
• Semester: First Semester
• Academic Year: 2023-2024

Course Aims

• Understand basic concepts and importance of well logging methods.
• Improve practical field survey and measurement skills for well logging.
• Develop specific interpretation techniques for well logging measurements.
• Employ a hands-on approach to basic open-hole well log analysis and interpretation, focusing on traditional targets like lithology, porosity, and fluid saturation.
• Introduce various computational and visual interpretation techniques, considering newer data and well-bore data (like cores, tests) to enhance and confirm interpretations.

Intended Learning Outcomes (ILOs)

• Knowledge and Understanding: Understand principles and theories of well logging methods, uses and importance of methods, recognize instrument elements, identify policy and field requirements for methods, and approach the principles of log data analysis, presentation, and interpretation.
• Intellectual Skills: Select appropriate field techniques, develop problem-solving abilities, differentiate between method applications, modify well logging methods for satisfactory information, and analyze well logging results in creative ways to report conclusions.
• Professional and Practical Skills: Perfect data analyzing and interpreting skills, manage data presentation, train exploration project design skills, train report-writing skills, and demonstrate differences between logging survey instrument types.

Teaching and Learning Methods

• Normal teaching methods (whiteboard/blackboard)
• Subjects and essay preparation
• Self-learning through library resources

Student Assessment Methods

• Written examinations (essay or MCQ)
• Practical examinations
• Oral examinations

Course Content

• Principles and mathematics bases (3 hours)
• Introduction to Logging Methods (6 hours)
• Self-potential and natural gamma ray (6 hours)
• Electrode resistivity/induction devices (6 hours)
• Porosity/density devices (6 hours)
• Mechanical devices (6 hours)
• Acoustic/optical/radar devices (2 hours)
• Quality Assurance (15 hours)
• Presentations (5 hours)

Facilities Required for Teaching

• Suitable class rooms with computers, data projectors, and slide projectors.

List of References

• Basic Well Log Analysis (Second Edition)
• Essential Books (Text Books) - An introduction to Geophysical Exploration, Philip Kearey.
• Principles of Applied Geophysics by D. S. Parasinis
• Geophysical methods in Geology by P.V. Sharma

Petrophysics

• Defined as the physical and chemical properties of rocks related to pore fluid distribution and crucial for hydrocarbon detection/evaluation.
• Key petrophysical parameters: Porosity, water saturation, and permeability
• Basic Measurements include Porosity and permeability assessment.
• Hydrocarbon Saturation can be directly measured from electric logs and indirectly from other logs.

Porosity

• Total Porosity: Ratio of pore volume to bulk volume.
• Effective Porosity: Ratio of interconnected pore volume to the bulk volume.

Resistivity

• Measure of rock material's resistance to electrical current flow.
• Influenced by water salinity, temperature, porosity, pore geometry, rock composition, and formation stress.

Permeability

• Measure of a porous rock's ability to transmit fluids (measured in darcy).

• Permeability theory: directly relates flow rate (-k * A * ΔP) / (Δl * μ) to permeability (k), fluid viscosity (μ), pressure difference (ΔP), length (Δl), and cross-sectional area (A).

• Porosity and Permeability Relationship for sandstone reservoirs commonly show a positive relationship, but for carbonate reservoirs the relationship is more complex.

Water Saturation

• Saturation percentage of porosity occupied by a specific fluid phase within the total bulk volume.
• Relationship: Sw (Water Saturation) + So (Oil Saturation) + Sg (Gas Saturation) = 100%

Deviated Wells

• TVD: True Vertical Depth, distance from a point in the well to the rotary table.
• TVDss: True Vertical Depth Subsea, vertical distance from a point in the well to the mean sea level.
• MD: Measured Depth.
• A: Azimuth
• The relationship between TVD, TVDss and MD is important to consider in deviated wells.

Well Logs

• A continuous record of measurements made in a bore hole.
• Responding to variations in physical properties of rocks.
• Include systematic recordings of rock properties and fluid content.

Log Acquisition

• Wireline Logging, Logging while Drilling(LWD)

Types of Well Logs

• Permeability and lithology logs (Gamma Ray, Self Potential (SP), Caliper logs)
• Porosity logs (Density, Sonic, Neutron logs)
• Electrical logs (Resistivity logs)

Borehole Environment:

• Gamma ray log measures natural radioactivity.
• Main radioactive elements: Potassium, Thorium, Uranium. K and TH occur mostly in shales.
• U from other sources.
• Primary use: indicates lithology (sand/shale).
• Gamma ray responses vary depending on minerals and lithologies.

Spontaneous Potential (SP)

• Records voltage difference between a moving electrode and a reference (mud pit).
• Requires conductive mud (not oil-based).
• Continuous recordings (approximately 1500 m per hour).

Factors affecting Spontaneous Potential (SP)

• Rmf/Rw Ratio: Ratio of mud filtrate resistivity to formation water resistivity affects SP deflections.
• Fresh mud: Higher Rmf results in + Ve SP.
• Saline mud: Lower Rmf results in -ve SP.

How to read an SP log:

• Sand with lower Rw than Rmf shows less deflection.
• Reverse deflection in sand indicates higher Rw: Formation water is fresher than mud filtrate.

Shale Volume Calculation

• Shale volume is often calculated using GR log measurements (GR responses to shale and clean formation).
• Methods and formulas for various rock types are used (Tertiary, Older Rocks)

Other Laboratory Topics & Calculations

• Temperature, Resistivity Calculations
• Determination of Rmf and Rmc from Rm
• Hydrocarbon Saturation
• Various Log evaluations (Chart uses relating different log parameters).

Additional Notes

• The provided documents contain detailed analyses of logs, practical exercises (like calculations), chart uses for specific situations and interpretations.
• Comprehensive procedures and step-by-step approaches for evaluation including calculations are described.