Deviation Survey

Navigating the Underground: Understanding Deviation Surveys in Oil & Gas

In the oil and gas industry, drilling for valuable resources often involves venturing deep underground. As the drill bit descends, it's crucial to ensure it stays on the intended path. This is where deviation surveys come into play.

What are Deviation Surveys?

Simply put, a deviation survey is a detailed record of the drillhole's trajectory. It tracks the deviation angle, which is the angle between the drillhole's axis and the vertical, and the departure, which is the horizontal displacement from the intended path. These measurements are usually taken on a depth unit basis, allowing engineers to visualize the drillhole's path in three dimensions.

Why are Deviation Surveys Important?

• Target Accuracy: Deviation surveys ensure the drillhole reaches the designated target zone, be it a specific reservoir or an existing well.
• Drilling Efficiency: Knowing the drillhole's trajectory helps optimize drilling operations by guiding the drill bit and minimizing unnecessary deviations.
• Safety and Cost Control: By predicting and managing potential deviations, surveys minimize the risk of wellbore instability, drilling complications, and costly re-entries.
• Formation Evaluation: Deviation surveys provide valuable information about the formations encountered during drilling, aiding in geological studies and reservoir characterization.
• Environmental Protection: They ensure the drillhole remains within the designated area, reducing the risk of environmental contamination.

Types of Deviation Surveys:

• Wireline Surveys: These are conducted using a wireline logging tool deployed in the drillhole, providing accurate and detailed information about the trajectory.
• Magnetic Surveys: Utilizing magnetic compasses, these surveys are less precise but offer a rapid and cost-effective way to track deviations.
• Gyro Surveys: These employ gyroscopes to determine the drillhole's orientation, offering high accuracy even in complex formations.

Data Analysis and Interpretation:

Deviation survey data is meticulously analyzed to create a detailed 3D map of the drillhole's path. This information is then used to:

• Develop drilling plans: Engineers can adjust drilling parameters to maintain the desired trajectory and optimize drilling performance.
• Forecast potential issues: Identifying areas of high deviation can alert engineers to potential wellbore instability or drilling challenges.
• Optimize production: Understanding the well's trajectory helps optimize production by ensuring the well is properly positioned within the reservoir.

Conclusion:

Deviation surveys are an essential tool in oil and gas exploration and production. They provide critical information about the drillhole's path, enabling engineers to navigate the underground effectively, minimize risks, and optimize drilling and production operations. By understanding the intricacies of deviation surveys, the industry can continue to explore and extract valuable resources safely and efficiently.