Correct display of the sonde location underground on the locator is one of the most important readings throughout the puncture path. In this article, we will talk about the causes for the incorrect display of the sonde location and its slant value. We will describe in detail how to check the location in the field.
The drill tour continued towards Siberia. I met our good customers OOO Truboplast, located in the city of Omsk. There were Alexander Anatolyevich, General Director, Eugene, location operator and Andrey Nikolayevich, Chief Engineer. At the meeting, the method of monitoring of antennas balancing was clearly tested using the ECLIPSE location system as an example.
Drill Tour — it is when we travel to the cities of Russia and meet drillers to exchange experience. We show our tips of working with the location and the colleagues-drillers ask questions and share experience in working at complicated facility.
When communicating, Eugene had a question to me: «Tell me, we’re already making the fourth puncture at this facility but in some parts of the route the location of the transmitter is not displayed correctly — „the ball goes to the side“. Though, in fact, the pilot is moving straight. What could it be?»
I replied that this could be passive interference or unbalancing of antennas. And this was easy to verify.
As you know, one of the causes for the incorrect transmitter location display on the locator is passive interference: reinforced concrete, iron pipelines, wells. With a strong source of passive interference (large volumes of reinforced concrete, for example), the transmitter’s magnetic field is distorted resulting in an error in indication of its location on the display. As they say — «We are starting to go in blind!»
This is a video instruction on how to pass the track with passive interference.
Active interference: power lines, electric installations, switched mode power supplies, moving trains or trams. The level of active interference is also easy to see on the locator’s display when the readings differ from zero, when the transmitter is turned off. Thus, before the puncture, you must turn on the locator (the transmitter is turned off) and see the level of interference along the path of the future puncture. Ideally, the display should show readings from 0 to 150 units (F-series locators may have negative readings). If the level of interference is higher, then the impact on the location of the transmitter gets proportionally increased and you may have complete loss of data from the transmitter on the display.
Below is the table of standard signal levels that the locator should display when the transmitter is turned on at a distance of three meters (calibration).
|Transmitter||Level of signal||Transmitter||Level of signal|
|ET/black||570||86BH black||two to three horizontal segments on the SubSite750 display (boost)|
If the readings of the transmitter on the locator differ upwards significantly, then, the level of active interference is too high. In this case, it is necessary to use a different frequency or an amplified (downhole) transmitter. At active interference level of approximately 300 units the maximum working depth does not exceed 5 meters further followed by data loss on the locator’s display.
Recommendations: before starting a puncture, always go through the entire drilling route with a locator measuring the level of interference. Depending on the parameters of your location, choose the optimal frequency at which the interference is lower.
For better understanding, I recommend reading the article on how to investigate the path for interference and select the optimal frequency.
There is another reason why the location of the transmitter is incorrectly displayed — this is possible malfunction of the locator antennas, the so-called «antenna unbalance». With long-term operation, falling (even from a small height) or mechanical damage to the locator, damage to the antennas is possible, the result of which is the wrong transfer of transmitter’s location.
The antenna malfunction can be checked even in the field. To do this, select the place where you have the minimum amount of external interference, start the locator and the sonde. On the locator fix the front location point FLP (located in front of the transmitter) and the rear point RLP (located behind the transmitter), approximately 0.5 meters above the sonde, so there is no overload of the locator (readings are less than 999).
Note: The higher is the locator, the greater is the distance between FLP and RLP.
At any location point, imagine you «build» a reference vertical axis under the locator in the center of the antennas (in the middle of the base front part of the locator) and turn the locator through 180 degrees.
RLP point was foun.
Turn the locator over the point found
If there is no unbalancing of antennas, then the ball remains in place, in the center. Your locator is working.
“The ball” remains in place
In the case of unbalancing of antennas, the location of the ball on the locator goes to the side, «floats».
We have checked everything and calibrated the location as well :)
As a result of checking the location, the unbalancing of antennas was not revealed. The main cause of deviation from the transmitter’s location was external passive interference. Eugene rejoiced at this result because repair of the location was not necessary. He thanked us for the detailed answer.
In conclusion, I would like to add that in fact there can be many causes for incorrect readings of the sonde location but first check for interference, then, antennas balancing, and only then look for the internal cause of the malfunction.
The locator is «responsible» for the accuracy to plot the coordinates of the transmitter underground; the sonde is «responsible» for the reliability of the data on the display (tilt, clock). And experience of the location operator also matters.