North Seeking Gyro Survey Tool vs. Reference Gyro Tool vs. Magnetic Survey Tool
When it comes to downhole survey tools, a gyro tool will always be the most accurate. Now, there are many types of downhole gyro survey tools, but it is widely accepted that north seeking, solid-state tools are the most accurate systems in the market.
The GyroMaster™ leads the pack thanks to its unique truly continuous mode, which collects data points at every centimeter along the borehole path. Every type of downhole survey tool has its advantages and disadvantages, which we are going to explore further in this article.
Magnetic Survey Tool
Old, but reliable, is the best way to describe this technology, however on certain applications, this technology is very outdated and even though you might save money upfront, you will lose much more in project value potential. We see more and more the magnetic tools being used as a validation tool, where companies will use this tool to show project potential and then invest in our north seeking GyroMaster ™ downhole surveying equipment.
The magnetic survey tool is more suited to low-cost requirements, whereas the north seeking gyro gives the required confidence and quality control needed for larger projects. A very common tool of the downhole survey industry, the magnetic tool is losing popularity as gyro technology becomes more affordable. However, this long-standing staple has allowed for much development and integration with other equipment specifically MWD (Measurement-While-Drilling) or LWD (Logging-While-Drilling). This application of the magnetic tool is widely used across the sector and has helped us as an industry move forward to improve efficiency. However, with more complex well profiles and multiple wells in close proximity, the north seeking GyroTracer with verified error model is becoming more prevalent throughout the industry.
Magnetically disturbed environment has always been this technologies downfall, but this tool has been an integral part of projects across the world for many years, obviously, these tools work well when the environment is magnetically free of disturbance. However, when accuracy is paramount, we always recommend to consider the north seeking GyroMaster™ with continuous mode.
Reference Gyro Survey Tool
One of the first introductions of gyroscopic sensors into the downhole survey industry was the reference gyro (free gyro). Although drastically inferior to the north seeking gyro, it helped pave the way for gyro incorporation into surveying.
Not affected by magnetic environments, this was the first point putting the gyro solution above the magnetic tool. Improved accuracy and easy to use, the reference gyro is a great all-round tool for short holes, however, that doesn’t mean it doesn’t have its negatives. Drift is a big problem for the reference gyro, and it is important that you understand the human error factor as these tools rely on starting data that is manually inputted.
A large group of gyro survey tool manufacturers are still selling mechanical gyro sensors. These tools are obsolete today and their calibration problems and temperature bias stability is also another big issue, but the biggest issue is the vibromechanical low resistance to impacts which max out at 15g compared to a solid–state solution, like the GyroMaster™, which can withstand up to 2000g.
As a manufacturer, SPT has discontinued all production of mechanical gyro sensors as they are truly an inferior technology, however, during its initial introduction, this technology was a breakthrough.
For certain applications, such as short holes in mining, a reference gyro can be a suitable option, however, for the majority of our clients, we recommend to use the GyroMaster™ north seeking continuous gyro tool, as it is the most versatile and accurate.
North Seeking Gyro Tool
The north seeker reigns king of downhole gyro survey tools. Unaffected by magnetism and consistently more accurate than the reference gyro, it allows the user to pinpoint targets with absolute values, rather than referencing manual inputs.
It is important to remember that not all north seeking gyros are the same. There are some providers who still use mechanical sensors and we’ve already discussed those negatives when we touched on reference gyros. For the purpose of this article, we will be speaking specifically about what Navibore™ technology provides. When deciding which tool to choose, remember to always ask the manufacturer the specifics and don’t assume every tool is the same. Some companies might even try to confuse customers with misleading accuracy measurements.
SPT’s truly continuous mode allows users to obtain data points at every centimeter and at all inclination ranges from completely vertical to horizontal. North seeking gyros that use SPT’s Navibore™ technology are able to eliminate all drift thanks to an automated quality control function that produces completely accurate data.
There is an example of an alternative gyro being used on a 1000–meter borehole where it was 60 meters off target. In comparison, the SPT tool using Navibore™ Technology was only 1 meter off. This type of discrepancy is the difference between project success and failure. We’ve also seen scenarios where a company bought rights to land for very cheap because a previous magnetic survey had deemed the area not profitable. However, when this company used our gyro survey technology, they came up with much more favorable results, which turned into a very smart initial investment.
Significantly quicker and much more accurate, the north seeking GyroMaster™ is the future of the downhole industry and is rapidly taking over the sector.
Downhole Survey Tool Summary
Magnetic survey tools have been around for a long time and are a cost–effective option for certain applications, however, their biggest disadvantage is they don’t work in magnetically disturbed ground and not suitable for intensive quality control measures. This paved the way for the adoption of gyro sensors in the downhole survey servicing industry.
Reference gyros are suitable for short hole solutions, however, they proved to be a problematic technology and many customers had to redrill the wells due to human error. This is because collar direction was dependent on external references (human), which many times were acquired by magnetic compass or magnetic reference point.
As with all technology, innovation pushes the limits and that’s where the north seeking gyro sensors based on solid-state technology came into play. Significantly more accurate than the alternatives, the north seeking GyroMaster™ has given a new definition to accuracy. Although more expensive, the results pay for themselves tenfold over the lifetime of a tool.
It is imperative to research and have a clear understanding of your project needs to make the right decision when choosing a downhole survey tool. Our technical team is happy to answer any questions that you might have regarding these types of tools. Don’t hesitate to contact us directly at [email protected].com.