CHL

Test Your Knowledge

Quiz: Cased Hole Logs (CHL)

Instructions: Choose the best answer for each question.

1. What does CHL stand for?

a) Casing Hole Logging b) Cased Hole Logging c) Completed Hole Logging d) Core Hole Logging

2. When are Cased Hole Logs typically performed?

a) Before drilling a well b) During drilling a well c) After a well has been drilled and cased d) During well completion

3. What is NOT a benefit of using Cased Hole Logs?

a) Improved reservoir understanding b) Efficient well management c) Lower drilling costs d) Safety and environmental protection

4. Which type of Cased Hole Log uses sound waves to assess casing thickness?

a) Nuclear logs b) Acoustic logs c) Electrical logs d) Production logs

5. What information can Cased Hole Logs provide about a well?

a) Formation properties and hydrocarbon presence b) Casing integrity and well performance c) Potential future interventions d) All of the above

Exercise: CHL Application

Scenario: An oil well has been drilled and cased. The operator needs to determine the best location for a new production zone. They have decided to run a Cased Hole Log to assess the reservoir properties.

Task: Based on the information provided below, explain how the Cased Hole Log data can help the operator make an informed decision about the production zone:

• Nuclear logs: Show high porosity and permeability in a specific zone between 3,000 and 3,200 feet.
• Acoustic logs: Indicate good cement bond quality around the casing.
• Electrical logs: Identify a hydrocarbon-bearing zone within the same depth range as the high porosity and permeability.

Write your explanation in a short paragraph.

Techniques

CHL: Deciphering the Language of Oil & Gas - Cased Hole Logs

This expanded document breaks down the topic of Cased Hole Logs (CHL) into separate chapters.

Chapter 1: Techniques

Cased hole logging employs a variety of techniques to gather data from behind the casing of a wellbore. These techniques utilize different physical principles to measure various properties of the formation and the well itself. The key techniques include:

• Nuclear Logging: This involves using radioactive sources and detectors to measure properties such as:

  • Density Logging: Measures the bulk density of the formation, providing information about porosity and lithology. Different isotopes (e.g., Cesium-137, Americium-Beryllium) can be used depending on the desired depth of penetration.
  • Neutron Porosity Logging: Measures the hydrogen index of the formation, which is directly related to porosity. Thermal neutron and epithermal neutron tools offer varying depths of investigation.
  • Gamma Ray Logging: Measures the natural radioactivity of the formation, helping to identify lithology and potentially, shale content.

• Acoustic Logging: This utilizes sound waves to determine:

  • Cement Bond Logging: Measures the quality of the cement bond between the casing and the formation. Poor cement bonds can lead to leaks and reduced well integrity. Variations include the use of monopole and dipole sources.
  • Casing Thickness Logging: Determines the remaining thickness of the casing, helping to assess its structural integrity.
  • Stoneley Wave Logging: A type of acoustic logging used to identify fractures and other formations characteristics.

• Electrical Logging: These techniques measure the electrical properties of the formation:

  • Resistivity Logging: Measures the resistance of the formation to the flow of electricity, which is inversely proportional to the conductivity. This helps identify hydrocarbons (which are poor conductors) and water (which is a good conductor). Various tools exist, like induction and laterolog, with different depths of investigation.
  • Spontaneous Potential (SP) Logging: Measures the natural electrical potential difference between the borehole and a reference electrode, useful in identifying permeable formations.

• Production Logging: This focuses on measuring parameters related to fluid production:

  • Flow Rate Measurement: Determines the flow rate of fluids in different zones of the well.
  • Pressure Measurement: Measures the pressure at different points in the wellbore, helping to identify pressure gradients and flow restrictions.
  • Temperature Logging: Measures the temperature profile of the wellbore, aiding in the identification of fluid flow and heat sources.

Chapter 2: Models

The data acquired from cased hole logs is used in various reservoir models to create a comprehensive understanding of the subsurface. These models often integrate CHL data with openhole log data, core analysis, and seismic data. Key models include:

• Reservoir Simulation Models: These complex numerical models use CHL data (porosity, permeability, saturation) to simulate fluid flow within the reservoir, predicting production performance and optimizing well management strategies.
• Petrophysical Models: These models use the log data to determine petrophysical properties like porosity, permeability, water saturation, and lithology. These models often use empirical relationships and statistical techniques to estimate these properties from the measured log responses.
• Geomechanical Models: These integrate CHL data (particularly cement bond logs) with stress data to assess the stability of the wellbore and the surrounding formation, which is critical for well integrity and preventing formation collapse.

Chapter 3: Software

Specialized software is essential for processing, interpreting, and modeling the data obtained from cased hole logs. These software packages typically offer a range of functionalities including:

• Data Processing: This involves correcting for various effects (e.g., borehole effects, tool drift) to enhance the accuracy of the log data.
• Log Display and Interpretation: Allows visualization of the log data, facilitating quick identification of key features and zones of interest.
• Petrophysical Calculations: Performs various petrophysical calculations to estimate reservoir properties from the log responses.
• Reservoir Simulation: Integrates the CHL data into reservoir simulation models to predict production performance.
• 3D Visualization: Provides 3D visualization of the reservoir and wellbore, offering a more comprehensive understanding of the subsurface. Examples include Petrel, Kingdom, and Schlumberger's Petrel software suite.

Chapter 4: Best Practices

Effective cased hole logging requires adherence to best practices throughout the entire process. These practices ensure data quality, accuracy, and safety:

• Careful Wellbore Preparation: Before running the tools, the wellbore should be properly cleaned and conditioned to minimize the interference of debris or fluids on log readings.
• Proper Tool Selection: Selecting the appropriate logging tools based on the specific objectives of the logging program and well conditions is crucial.
• Quality Control: Rigorous quality control procedures should be implemented throughout the logging process to ensure the accuracy and reliability of the data.
• Data Calibration and Correction: Appropriate calibration and corrections should be applied to the data to account for various environmental and tool-related effects.
• Experienced Personnel: CHL interpretation requires the expertise of qualified engineers and geologists to correctly analyze and interpret the data.

Chapter 5: Case Studies

Illustrative case studies showcase the application of CHL techniques and their impact on decision-making in oil and gas operations. These case studies will depend on publicly available information and may include:

• Case Study 1: Example of using CHL to identify a previously undetected hydrocarbon zone, leading to improved production.
• Case Study 2: Example of using CHL to assess casing integrity and identify a potential leak, preventing environmental damage and production loss.
• Case Study 3: Example of using CHL data in reservoir simulation to optimize production strategies and maximize recovery. (Specific details will depend on available data).

This detailed breakdown provides a more complete and structured understanding of Cased Hole Logs and their importance in the oil and gas industry. Remember that specific examples and details within the case studies will need to be sourced from publicly available information or industry reports for ethical and confidentiality reasons.