by Orlando Ramirez, Founder & CEO, Stockholm Precision Tools AB – Sweden (SPT)
When it comes to the exploitation of ore bodies, the accurate measurement of trajectories (borehole surveys) – both in the exploration and production phases – is a factor that those responsible for geology, drilling and planning departments must consider. The main factors that influence borehole deviation are the drilling parameters, the geological structure, the drilling method used and other miscellaneous factors.
Many companies and investors commit to projects that initially seem very promising, but as they progress, the results obtained are not as expected. One of the most frequent causes for this is that the simplest of factors are ignored, and due to lack of knowledge, certain important criteria are not met, such as an accurate trajectory measurement for every borehole drilled or the use of incorrect technology combined with the absence of exhaustive quality control of the tools used.
All investors want to obtain the optimum results and benefits from the capital they have invested, but unfortunately, they often rely on people who do not understand the importance of an accurate measurement of the well trajectory or more practically, the relative accuracy of different tools and survey methods. The spatial location and the exact orientation of the core are key to accurate determination of the existence of ore and volume of rock waste for disposal.
Other related factors that have an impact on the poor delineation of an ore body are the survey tool selection criteria – often based on the lowest cost without any detailed technical analysis of the relative and absolute advantages and disadvantages of the different survey tools.
Why are gyroscopes so important?
A gyroscope is any rotating body that exhibits two fundamental properties: gyroscopic inertia or ‘rigidity in space’ and precession, which is the inclination of the axis at right angles to any force that tends to change the plane of rotation. These properties are inherent to all rotating bodies, including the Earth.
Gyroscopic inertia and the force of gravity can be used to make the gyroscope function as a directional indicator or compass. If one considers a gyroscope mounted at the Earth’s equator, with its axis of rotation lying in the east-west plane, the gyroscope will continue to point in that direction as the Earth rotates from west to east. Thus, the eastern end will rise relative to the earth, although it will continue to point in the same direction in space. It resists this force and generates a precession motion about the vertical axis, toward the meridian so that the axis of the gyroscope seeks and maintains the true meridian, i.e., points in a north-south direction.
Since a Gyro’s method of operation is based on the earth’s rotational force and not on magnetism, the north seeking gyroscope, such as SPT’s GyroMaster, is much more versatile in its applications and is increasingly being used in major geological and mining projects.
Types of gyroscopes: Reference vs. North seeking.
We can distinguish between different types of gyroscopes: the true north seeking gyro (NSG) and the reference gyro.
Unlike the north seeking gyro, the reference gyro lacks a sufficiently accurate sensor to measure the Earth’s angular velocity projection. The reference gyro is not capable of finding North, which means that it cannot establish an azimuth itself. In order to perform its survey function, it needs manual input at startup. We sometimes name these instruments as reference or indirect measuring inclinometers (not actually a very good name!). However, the reference gyroscope is sufficiently accurate, slimmer, and robust enough for short blasthole surveys if an accurate start azimuth is available.
Azimuth is the direction of a wellbore in the horizontal plane, expressed in degrees (°) with respect to magnetic or geographic north.
The inclinometer, as the name implies, is a tool that measures the inclination of a borehole and does not measure direction directly but takes it from an external point and its data accuracy depends on this external input, and hence there is room for potential cumulative errors to be generated as the survey proceeds along the borehole. But the measurements made by these tools are not only inclination, but also direction (azimuth). Since reference gyros lack the technology and the sensor needed to find true North and establish an azimuth, they cannot survey vertical boreholes.
SPT’s GyroMaster is a true north seeking gyro capable of measuring even at +/- 90° angles. Its performance and accuracy have been proven in adverse conditions. GyroMaster is an excellent tool for use in boreholes that are near one other, where the highest possible accuracy is required.
It should therefore be clear that the use of reference gyroscopes in extremely important mining projects is not always the best choice, as their performance depends on the starting datum, if provided with the wrong starting datum, the whole measurement would be wrong.
The same happens with other gyroscopes that are true north seeking, but which are unable to provide consistent, repeatable, measurements between the in and outrun surveys to/from the borehole, so it is appropriate to classify them as true north seeking gyroscopes, but of low accuracy.
Equally disastrous for exploration mining programs is the use of reference gyroscopes as low-accuracy north finders. Low-precision gyroscopes are remarkably similar to reference gyroscopes. Some of these even obtain the initial reference point using a magnetic compass.
Spt offers a gyro for every need
The GyroMaster is a north seeking gyro designed with Navibore technology, created by SPT. In addition to all the advantages mentioned above, GyroMaster is very easy to use thanks to its intuitive software. It is perfect for continuous measurements during any drilling operation. Thanks to its proven reliability, with approximately 1200 MTBF, we can proudly say that the GyroMaster is unbeatable. It is also compatible with the SPT SmartCloud, which allows cloud synchronization of all mining projects.
In summary, the gyroscope is a multi-purpose tool and there are different types. It is used in many areas and ideally, you should select the gyroscope that best suits your project needs. Visit the website www.sptab.com to consult the wide catalog of gyroscopes and other solutions for borehole surveying that we have at your disposal.
We participated in PDAC 2022 where we offered a spectacular augmented reality experience for all visitors. Thanks to this technology visitors could discover our tool capabilities in a unique and special way. We are already preparing to surprise the public at the next PDAC 2023, scheduled for March, 2023.
For more information schedule a session to test our tools directly in your mine for free and without any obligation. Or visit: www.sptab.com
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