Gyroscope Surveying Technology and Tools
A gyroscope, or gyro, is a device designed to measure or maintain orientation based on the principle of conservation of angular momentum. This principle dictates that a rotating object inherently resists alterations to its orientation due to the momentum generated by its spin. Typically, a gyro consists of a centrally rotating mass, often referred to as a rotor, which preserves its axis of rotation when subjected to external forces. This inherent resistance facilitates the detection of rotational movements around its axes, enabling precise measurements of direction and orientation.
The operational efficiency of a gyroscope is fundamentally linked to its spinning mass. As this mass spins, it produces angular momentum that counteracts any external torque attempting to modify its orientation. By analyzing these resistance forces, the gyro can accurately gauge both the rate and direction of rotation. Gyroscopes have applications in many fields due to their ability to determine orientation without being affected by external references, such as magnetic fields.
Gyro tools offer higher accuracy because they utilize gyroscopic technology to measure true north, thereby avoiding errors caused by magnetic interference. MWD tools often rely on magnetic sensors, which can be inaccurate near cased holes or other wellbores where magnetic fields are distorted. MWD tools utilize magnetometers for azimuth and require correction for magnetic declination, whereas gyro surveying tools do not.
Common Gyro tools used in oil & gas drilling operations:
Various types of Gyro tools are used in oil and gas drilling depending on the needs of the application:
1. Single Shot Gyro:
A single-shot gyro is used in oil and gas drilling to measure the orientation of a wellbore at a specific depth. It captures a single wellbore inclination and azimuth measurement at a predetermined point. A single-shot gyro focuses on a single particular location per deployment. Single-shot gyros are used when a quick one-time measurement is sufficient. It is a useful tool for quick trajectory checks, deviation verification, and tool orientation in areas with magnetic interference. Single-shot gyro surveys have the advantage of simple setup, facilitating quick deployment and retrieval. It’s less expensive than advanced multi-shot or continuous gyro tools, making it an economical choice for specific scenarios.
The tool is lowered into the wellbore in one of two ways:
Wireline: The gyro is attached to a wireline, which is lowered inside the drill string to the intended depth. Once at the target depth, the gyroscope activates manually or automatically to measure inclination and azimuth. After recording the data, the tool is retrieved by pulling it back to the surface via wireline.
Drop Method: In this deployment method, the tool is dropped down in the drill string, free-falling through the drilling fluid to a landing point at the desired depth. This method is beneficial when traditional wireline access is challenging or time-consuming, such as in high-deviation or horizontal wells where wireline tools may struggle to reach the bottom or when a quick survey is needed without the setup time required for wireline equipment. A landing ring is run in the drill string where the gyro tool lands. Once at depth, the gyroscope measures the wellbore’s inclination and azimuth. After completing the survey, the tool is retrieved by pulling the drill string or using a wireline to fish it out of the well.
2. Multi-shot Gyro:
A multi-shot gyro is an advanced surveying tool used in oil and gas drilling to measure the trajectory of a wellbore at multiple depths in a single deployment. Unlike a single-shot gyro, which captures data at one specific point, a multi-shot gyro takes measurements at various intervals, providing a detailed profile of the well’s path. It records key parameters such as inclination and azimuth to ensure accurate wellbore placement.
The tool is typically lowered into the wellbore using a wireline. In some cases, it can also be deployed on coiled tubing or slickline. As the tool moves through the well, it takes measurements at predetermined intervals, such as every 30 feet or 10 meters. At each point, the gyroscope calculates the inclination and azimuth. Some multi-shot gyros can also measure additional parameters, such as tool face orientation or temperature. The tool either stores the data internally for retrieval when it is brought back to the surface or transmits it in real time to the surface via the wireline. This process enables the multi-shot gyro to generate a series of "shots" or data points, mapping the wellbore’s trajectory in a single run.
Multi-shot gyros are utilized when a precise understanding of the wellbore’s path is crucial. Such as complex trajectories where multiple measurements are required to ensure the well stays on its intended course or for post-drilling surveys to confirm the final wellbore trajectory after drilling, ensuring it aligns with design specifications. The multi-shot gyro offers several advantages over single-shot tools or other surveying methods. It captures multiple measurements in one run, reducing operational time and costs compared to repeated single-shot surveys. It provides a detailed trajectory profile, improving accuracy in wellbore placement while minimizing the risk of errors due to potential magnetic interference.
3. Continuous Gyro:
A continuous gyro is an advanced surveying tool used in oil and gas drilling to provide real-time, uninterrupted measurements of a wellbore's trajectory. Unlike traditional tools, such as multi-shot gyroscopes that take discrete measurements at specific intervals, a continuous gyro delivers a constant stream of data as it moves through the wellbore. It measures the wellbore's inclination and azimuth, offering a highly detailed and accurate profile of the well's path. This precision ensures accurate wellbore placement, particularly in complex drilling environments.
Modern continuous gyros often employ solid-state technologies, such as Fiber Optic Gyros, which uses light to measure angular velocity, or Ring Laser Gyros, which uses laser interference for high-precision measurements. These technologies are more durable and accurate than traditional spinning-mass gyros. The continuous gyro is mounted in the bottom hole assembly (BHA) as part of the drill string. As drilling progresses, it provides real-time data to the surface, enabling immediate adjustments to the drilling direction. The tool can also be run on a wireline after drilling a section of the well. It is lowered into the wellbore, and continuous data is recorded as it is raised or lowered. In both configurations, the tool transmits data in real time or stores it for later analysis, depending on the setup.
As an advanced technology tool, continuous gyro and real-time capabilities are more expensive than those of conventional tools like multi-shot gyros. Data analysis also requires specialized equipment and sophisticated software. Hence, a thorough cost-benefit analysis is needed to decide on deploying this technology. A continuous gyro is a suitable option in scenarios requiring high precision and real-time control for complex well trajectories, such as highly deviated, horizontal, or extended-reach wells, where maintaining the correct path is critical. Densely drilled fields with multiple magnetic interference zones and narrow windows for well maneuvering pose a high risk of well collision. They are strong candidates for deploying continuous gyro and real-time capabilities to ensure accurate well placement.
4. Gyro MWD:
A Gyro Measurement While Drilling (Gyro MWD) tool is an advanced surveying instrument used in oil and gas drilling operations to measure the wellbore's trajectory in real time. Unlike traditional Measurement While Drilling (MWD) tools that rely on magnetic sensors, Gyro MWD incorporates gyroscopic technology to provide accurate orientation data, particularly in environments where magnetic interference compromises the reliability of standard MWD systems. A Gyro MWD tool enhances drilling precision by integrating gyroscopic sensors into the MWD system to ensure precise wellbore placement in complex or densely drilled fields.
Gyro MWD integrates gyroscopic sensors into the MWD system, which measures the Earth’s rotational rate to determine the wellbore’s inclination and azimuth. Unlike magnetic sensors, gyroscopes are unaffected by magnetic fields, making them ideal for areas with interference, such as near steel casings or fields with multiple wells. The Gyro MWD tool is mounted in the bottom hole assembly (BHA) and is placed close to the drill bit. Data is transmitted to the surface through mud-pulse telemetry or electromagnetic signals, allowing drillers to adjust the drilling path instantly.
Gyro MWD is helpful when traditional magnetic MWD tools may be unreliable and insufficient. Drilling through high Magnetic Interference Zones, such as near steel casing exits or in fields with closely spaced wells where magnetic fields distort readings, may require more reliable tools to minimize the risk of collision with existing wells nearby. High-inclination or Horizontal Wells with complex trajectories require real-time data for precise control and accurate placement. The gyro MWD tool can switch between gyro and MWD modes as needed. Hence, it increases operational efficiency and reduces downtime by eliminating separate wireline gyro surveys for well trajectory confirmation in high-magnetic-interference zones.
5. Gyro While Drilling (GWD):
A Gyro While Drilling (GWD) tool is a specialized surveying instrument used in oil and gas drilling to measure the wellbore's real-time trajectory. GWD is integrated into the drilling assembly, specifically the bottom hole assembly (BHA), and is used during the drilling process. It is designed to operate in real-time, collecting data as the well is being drilled. Deployment typically involves wireless communication methods, such as mud-pulse or electromagnetic systems, to transmit data to the surface without interrupting drilling operations.
Gyro While Drilling (GWD) provides the benefit of acquiring accurate inclination and azimuth data, even in high Magnetic Interference Zones near steel casings or in fields with multiple wells, where magnetic fields distort readings from magnetic tools like MWD, and avoids well collision. It is also useful when drilling complex well paths, such as high-inclination, horizontal, or extended-reach drilling (ERD) wells, providing real-time data for precise trajectory control.
Difference between Gyro While Drilling (GWD) and Continuous Gyro:
While Gyro While Drilling (GWD) and Gyro MWD are similar in terms of benefits, data collection, and communication, they differ in many ways:
Deployment: GWD is integrated into the drilling assembly, specifically the bottom hole assembly (BHA) used during active drilling. Meanwhile, continuous Gyro can be deployed in various ways, depending on its application, such as on wirelines, slicklines, coiled tubing, or even as part of the BHA in some cases.
Application: GWD focuses on real-time steering and guidance during drilling, while Continuous Gyro emphasizes detailed trajectory surveying, typically for post-drilling analysis or in non-real-time applications.
Data Frequency: Continuous Gyro provides more frequent data points due to its uninterrupted measurement capability, while real-time transmission limits constrain GWD.
Accuracy: Continuous Gyro is generally more accurate, especially in controlled conditions, though GWD offers high precision tailored to drilling demands.