electric survey

Electric Surveys: Illuminating the Secrets Beneath the Surface

In the world of oil and gas exploration, understanding the subsurface is paramount. This is where electric surveys, also known as electric well logs, come into play. These powerful tools provide a detailed glimpse into the geological formations encountered during drilling and well completion, guiding crucial decisions for successful resource extraction.

What are Electric Surveys?

Electric surveys involve lowering specialized instruments, called logging tools, down the wellbore. These tools measure various electrical properties of the rock formations, such as:

Resistivity: The ability of a formation to resist the flow of electricity. This reveals the presence of hydrocarbons, water, or gas, as each has a distinct resistivity signature.
Porosity: The amount of empty space within a rock formation, which determines its ability to store hydrocarbons.
Permeability: The ability of a formation to allow fluids to flow through it, crucial for hydrocarbon production.
Formation Density: The density of the rock formation, which helps identify different lithologies (rock types).
Sonic Velocity: The speed at which sound waves travel through the formation, providing information on rock type and porosity.

Types of Electric Surveys:

Different types of logging tools measure specific properties, leading to various electric survey types:

Resistivity Logs: These logs measure the resistance to electrical current, revealing the presence of hydrocarbons and the location of potential pay zones.
Porosity Logs: These logs measure the pore space within the rock, helping determine the reservoir's potential for storing hydrocarbons.
Permeability Logs: These logs measure the ease of fluid flow through the rock, crucial for understanding the producibility of a reservoir.
Density Logs: These logs measure the density of the rock formation, helping identify lithologies and potential pay zones.
Sonic Logs: These logs measure the speed of sound waves through the rock, providing information about the rock's composition and porosity.
Nuclear Logs: These logs use radioactive sources to measure various properties like density, porosity, and lithology.

Applications in Drilling & Well Completion:

Electric surveys play a crucial role in various stages of drilling and well completion:

Formation Evaluation: Identifying potential pay zones, characterizing reservoir properties, and guiding the selection of drilling mud.
Well Completion Design: Determining the optimal completion strategy, including the selection of casing and perforation intervals.
Production Optimization: Monitoring reservoir performance, identifying potential problems, and optimizing production rates.
Reservoir Management: Understanding reservoir architecture, fluid movement, and well performance, aiding in maximizing recovery.

Summary:

Electric surveys are indispensable tools in the oil and gas industry, providing valuable insights into the subsurface. They enable efficient exploration, well planning, completion design, and production management, ultimately contributing to the successful discovery and extraction of hydrocarbons. By illuminating the secrets beneath the surface, electric surveys empower the industry to make informed decisions and maximize its resource potential.

Test Your Knowledge

Electric Surveys Quiz:

Instructions: Choose the best answer for each question.

1. What is the primary purpose of electric surveys in oil and gas exploration?

a) To measure the temperature of the Earth's crust. b) To locate underground water sources. c) To provide a detailed understanding of subsurface geological formations. d) To determine the age of rocks.

Answer

c) To provide a detailed understanding of subsurface geological formations.

2. Which of the following properties is NOT measured by electric surveys?

a) Resistivity b) Porosity c) Magnetic field strength d) Sonic velocity

Answer

c) Magnetic field strength

3. Which type of electric survey is specifically used to determine the ease of fluid flow through rock formations?

a) Resistivity Logs b) Porosity Logs c) Permeability Logs d) Density Logs

Answer

c) Permeability Logs

4. Electric surveys are used in which stages of drilling and well completion?

a) Only during exploration. b) Only during drilling. c) Only during well completion. d) Throughout the entire process, from exploration to production.

Answer

d) Throughout the entire process, from exploration to production.

5. What type of electric survey uses radioactive sources to measure subsurface properties?

a) Resistivity Logs b) Porosity Logs c) Nuclear Logs d) Sonic Logs

Answer

c) Nuclear Logs

Electric Surveys Exercise:

Instructions: Imagine you are an oil and gas exploration geologist. You are analyzing electric survey data from a newly drilled well. The data reveals the following:

Resistivity Logs: High resistivity readings in a specific interval.
Porosity Logs: High porosity readings in the same interval.
Permeability Logs: Moderate permeability readings in the same interval.

Based on this information, describe the potential of this interval as a hydrocarbon reservoir. Justify your answer.

Exercice Correction

This interval has strong potential as a hydrocarbon reservoir. Here's why:

High resistivity readings suggest the presence of hydrocarbons, which are poor conductors of electricity.
High porosity readings indicate that the rock formation has a significant amount of pore space, which can hold hydrocarbons.
Moderate permeability suggests that while fluids can flow through the rock, it might not be exceptionally productive. However, this can be further evaluated with additional testing.

Overall, this interval shows promising characteristics for a potential hydrocarbon reservoir. Further analysis and testing are needed to confirm its viability.

Books

"Log Interpretation Charts" by Schlumberger: A comprehensive guide to interpreting well logs, including electric logs, with numerous charts and diagrams.
"Well Logging and Formation Evaluation" by Schlumberger: This book provides an in-depth overview of well logging techniques and their application in formation evaluation.
"Petroleum Engineering Handbook" by SPE: This handbook contains a section on well logging and formation evaluation, providing a broad overview of the topic.
"Reservoir Engineering Handbook" by SPE: This handbook covers aspects of well logging related to reservoir characterization and management.

Articles

"Electric Logging: Principles and Applications" by M.B. Dobrin: A classic paper explaining the fundamental principles of electric logging and its various applications.
"The Evolution of Well Logging: A History" by Schlumberger: This article traces the development of well logging technology from its early days to modern advancements.
"Advanced Logging Techniques for Improved Formation Evaluation" by SPE: This article explores recent developments in well logging techniques and their impact on formation evaluation.

Online Resources

Schlumberger's "Oilfield Glossary": A comprehensive glossary of oilfield terms, including detailed definitions of various electric log types.
SPE's "OnePetro" platform: This online platform offers numerous articles, technical papers, and presentations related to well logging and formation evaluation.
"The Well Logging Society (WLS) website": This website provides information on well logging practices, training resources, and industry events.

Search Tips

Use specific keywords: When searching for information, use specific terms like "electric well logs," "resistivity logging," "porosity logging," or "sonic logging."
Specify the context: Include keywords like "oil and gas," "hydrocarbon exploration," or "reservoir characterization" to narrow down your search results.
Combine keywords with operators: Use "+" to include specific terms in your search, "-" to exclude terms, and "" to search for an exact phrase.
Search for specific authors or organizations: Use "author: [author name]" or "site: [website name]" to find articles or resources from particular sources.