Introduction
The Flexit tool orients advanced piston corer (APC) cores by taking orientation measurements for a short period of time just prior to when the core is taken. The drill string is kept steady while the tool measures and stores measurements from a triaxial magnetometer and a triaxial accelerometer. The data output includes hole ID, dip, azimuth, temperature, magnetic tool face, magnetic field strength, magnetic dip, and accelerometer output. The orientation tool is run on the APC bottom-hole assembly (BHA) within a nonmagnetic core barrel. The tool is synchronized with a PC computer and the MeasureIt software before deployment. After deployment the recorded data are downloaded to the the PC via wireless communication.
Theory of operation
Earth’s total magnetic field strength varies at any particular point on Earth. The field is characterized by six parameters: declination, inclination, horizontal intensity (north and east components), vertical intensity, and total intensity. Magnetic field strength values increase toward the poles but only change minimally with borehole depth. Declination is the angular difference between true (geographic) north and magnetic north. Inclination is the angle at which the magnetic field lines intersect the surface of the earth (ranging from 0° at the Equator to 90° at the poles).
The core orientation process determines the angular correction to apply to the core’s declination values as measured by the cryogenic magnetometer. The Flexit tool is connected to the core barrel in such a way that the double lines on the core liner are at a fixed known angle to the sensors. The Flexit tool records an azimuth to magnetic north for each core. This azimuth combined with the local magnetic declination values allows the scientists to correct the measured core declination's back to the true coordinates.
The Flexit tool and brass pressure case kit.
Software Installation:
If you are installing the software on a new computer, you must register the tools after installing the Flexit software, version 3.5 (on the TAS/Software volume). Click the Set-Up button, then click the Tool Set-up and Register SmartTool buttons respectively. Type in the serial number and registration codes for each tool one at a time and then click Register This. The tool(s) will then be available for you to select when setting up for a run. Ignore any screens about sending off the registration information.
IODP Flexit Tool Information
s/n | Reg. number |
0936 | D1AA8F4A9B1 |
0937 | 9A952918021 |
Tool Setup
After arriving on site the technician will edit the default survey data to reflect the proper geomagnetic values for the area:
- Get the latitude and longitude of the location from the Bridge and go to the website http://www.ngdc.noaa.gov/geomagmodels/struts/calcIGRFWMM where a calculator will provide the proper values. If the Internet is not available, please see Appendix 1.
- Open MeasureIT, press Set-up and then Default Survey Data buttons to edit the Magnetic Field and Dip values for the magnetic Integrity Check (MagIC). You may have to move the slider down on the left hand side to access that part of the window (Figure 1A). Hit Exit when finished to return to the main menu.
- Default Survey Data is also where measurement units are set.
- Default Survey Data is also where measurement units and intervals are set. The Tool Setup button (Fig. 1B) is where you set your default file location for surveys as well as enable Time-Based Continuous Survey (TBCS) mode.
Figure 1A Default Survey Data screen
Figure 1B Specifying file location for your surveys and enabling time based continuous survey mode.
Starting a Survey
- Have your unjacketed tool within a 5-10 meter line of sight to the TransIT PC adapter attached to the computer’s serial port.
- From the MeasureIT main menu, press the Survey Sessions button. Select your tool’s serial number (printed on the tool casing) from the list and hit Continue.
- Verify that the tool is talking by clicking Measure Angles. (Most likely the data will make little sense inside the ship because of all the steel but the tool should be at least measuring and reporting.) Move the tool around and ensure that Measure Angles reports the changes. If not, make sure you are linking with the right tool! Our tools are stored close to each other and may also link if selected incorrectly, depending on your location.
- Click the radio button for Time-based continuous survey as indicated in Fig. 2. Hit Continue when finished. Note that at a minimum 6 seconds between shots you have about 27 hours to acquire data before the memory fills up. Our tools have been run as long as 25 hours without incident, but it may be advisable to pull them every 8-12 hours to avoid too much data loss in case of problems.
Figure 2 Tool check/survey type selection screen
5. You will be presented with a window telling you that it’s time to start your synchronization file for depths. We do not have to create this file just yet; it will be used during the processing phase though.
6. Additional windows appear with status information about tool initialization; hit Continue if everything is okay.
7. Give the survey a name, such as “{Site}-{Hole}-{start core}-{end core}” or similar (Figure 3). The other fields should be ignored. Hit Continue when finished. Note that “the clock is ticking” so avoid starting a survey hours before handing the tool to the Core Techs (CT’s).
a. If the survey has started, the window will appear as in Figure 4.
Figure 3 Survey naming and unit selection screen
Figure 4 Real-time measurement status screen
8. The tool is now ready to go. Place it in its brass pressure case, snug up the end pieces and turn it over to the Core Tech (Figure 5A-B).
Figure 5A: Insert the tool into the pressure case’s open end as shown (keyway out)
Figure 5C: slide the key end of the other end seal onto the Flexit tool, insert it into the barrel and tighten. Hand the assembly to the Core Tech for final rigging with the snubber shock and IODP pressure case.
9. Keep track of the times that the tool is on bottom. Stand pipe pressure data and the time on deck for each core can be used to determine when the tool was on bottom. Standpipe pressure peaks just before the core barrel is fired into the sediment, so the orientation period is ~5 minutes before the peak. Please see an ET or Ops Supervisor for a demonstration on accessing the standpipe pressure data.
Data Retrieval and Processing
This version of the software can only do one thing at a time when performing continuous surveys, so you won’t be able to configure another tool on the same computer while the first tool is still waiting to have its survey ended. Therefore, if orientation continues and you need a second tool to give to the CT’s then it will have to be configured on a different computer that is also running the Flexit software and has a TransIT transceiver attached. Then it can be measuring while you download the data on the first tool from the starting computer. We have a site license for the software, so it can be installed on as many PC’s as necessary, but only three TransIT radio-sync devices exist.
- Just before or after receiving the tool from the CT’s, unload the tool from its brass pressure case and keep it within a 5 meter line-of-sight of the TransIT adapter to the computer. Return to the measurement screen and click End Survey. An option to download the data follows.
- A confirmation screen appears to make sure you really want to finish the survey (Figure 6). Select End Survey Session.
Figure 6 End survey confirmation screen
3. Click Start Download to begin the data download (Figure 7). You’ll need to select your tool from the list as before.
a. It takes about a half-second per shot for the data to download, e.g. an 8-hour survey at 6 sec/shot should take around 40 minutes to download. The downloading survey window will be displayed throughout the download process (Figure 8).
Figure 7 Start the download process
Figure 8 Download-in-progress screen
4. After downloading the data processing screen appears (Figure 9). This is where you will select the synchronization file.
Figure 9 Preliminary downloaded data screen
5. Now it is time to create the synchronization file. It has a very specific format and is a text file. The first line must have the following string:
SynchTime=DD/MM/YY HH:mm:ss
Where DD=day, MM=month, YY=year, HH=hours, mm=minutes, and ss=seconds. You can find this exact time stamp at the top of the download screen as indicated in Fig. 9. The following lines in the file are semicolon-delimited strings. The name of the file can be anything, but you might consider using a name like “sync_{site-hole-core range}.txt” for clarity.
6. Get the time-on-bottom (TOB) information from the drillers for the range of cores covered by this survey. For each TOB, determine the number of minutes from the time you started the survey until the Flexit tool was on bottom orienting. Assume you have the normal 5 minutes per core of orientation time. For example, say that the start time is 1000 or 10:00 AM. Let’s say that the tool was on bottom for core 9H at 1028 hrs. So that’s 28 minutes or 1680 seconds into the record. The core was oriented for 5 minutes (300 seconds). Therefore the window will lie between 1680 seconds and 1980 seconds into the record. Let’s say the shot interval is every 6 seconds. Thus you will need to add one line per shot point at 6-second intervals to the sync file with the following format after the first line:
SynchTime=22/01/09 10:00:00
1680;9
1686;9
1692;9
1698;9
*
*
*
1980;9
The number after the semicolon denotes the number of the core being oriented. Do the same sort of calculation and formatting for the rest of the cores in the survey. When this file is finished, it will help the Flexit software pre-select the records of interest from the data dump.
7. Apply your Synch file to the data. By the heading “Depth/Time reference file” click Browse/Select and locate your synch file. Click Apply Depth/Time.
8. Scroll down the data window. You will see your windows of interest highlighted in green. Any suspect data that fails the non-optional Gravity check (1G +/- 2%) will be flagged in lighter green with red text.
9. Click the Process Selected Records as Survey (Figure 9). A file named {your survey name}_FLT.svy is created. This will calculate the values for Magnetic Tool Face (MTF), the primary information IODP uses to orient cores, as well as a variety of other data.
10. Proceed to the Multishot Calculation Stage 1 screen (Figure 10). Click the ‘Do not review’ button to skip the data review screens. They are of limited use to us because we are not performing a “traditional” downhole survey..
Figure 10 Stage 1 calculation options screen
11.
12. The final screen will reveal the results of the survey (Figure 11). You can review both the raw and processed survey files by navigating to the file location you specified as shown in Fig. 1B. All files are in ASCII text despite the file type suffix (.rsy=raw survey, .svy=data-reduction results, .csy=continuous survey, .dtf=depth/time file).
Figure 11 Final results (for our purposes, “Station” = measurement every 6 seconds)
13. The next step is to calculate out the number of the first station that should be very close to the orientation window for each core. Consider that station numbers in a survey file are time proxies, i.e. each station represents 6 seconds. You can get the tool initialization time and date from either the raw or processed survey file (in GMT since IODP workstations are set to that zone). It may be easier to convert the time to local ship’s time for the processing step and to recollect the timing of some operational details that may pertain to the orientation data.
Example: tool start time (from the raw survey file) was 5:25 am local or 0525 hours. According to the standpipe pressure data and time on deck, the tool was on bottom and orienting at 0737 hours for core 3H, 0853 hours for core 4H, and 1012 hours for core 5H. The time difference from tool initialization to core 3H is 132 minutes. Multiply by 10 shots/minute since our tools measure every 6 seconds and you get 1320 measurements taken before you should see your orientation window begin. Similarly, there is 76 minutes between time-on-bottom (TOB) for core 3H and 4H, so add 760 to core 3H’s starting point of 1320. Your window for core 4H should start around station #2080. Finally, core 5H’s window will be around station #2870 since there were 79 minutes or 790 shots between core 4H and 5H.
14. Copy the data portion of the processed survey file (*_FLT.svy) into Excel and parse it. Hide or delete columns of no interest such as Easting, Northing, Elevation, UpDown, LeftRight, Shortfall, ToolRoll, and DLS. Optional - for ease of scanning apply conditional formatting to the Temperature, Magnetic Field and Gravitational Field columns: change cell’s color if temperature is below 3° C (your bottom hole temperatures may be higher), Mag. Field is less than 50000 nT (check field model for your location and add a ‘fudge-factor’ for the drillstring) and Gravity is less than .980 or greater than 1.02. Scroll down the processed survey file to the station numbers you calculated in step 10. You should see very repeatable data particularly in the MTF, temperature, and magnetic dip fields. Suspect gravitational field measurements will have changed color from conditional formatting making them easy to delete from the total records to be averaged. Average your ‘clean’ records and provide the MTF value to the paleomagnetists. Consider keeping a table with other statistics such as the standard deviation, number of readings averaged, and approximate time spent orienting for each core[MH1] . (Fig. 11).
[MH1]editors: we are still finalizing this part; I’m referring to what I did on Exp. 321
Appendix 1: Using the offline geomagnetic field calculator software
1) Copy the software from TAS/Software/labsystems/Flexit/geomagnetic field calculator/Geomag61_windows folder to your local PC.
2) Double-click the Geomag.exe program in your new folder.
3) Follow the onscreen prompts. Enter IGRF10.cof for your model, although either model should give similar results for our purposes.
4) Choose option 2, month, year and day for the date entry.
5) Choose 1, single date for the range option.
6) Enter the year, month and day as requested.
7) Select option 1, Geodetic coordinates.
8) Select option 2, meter units.
9) The geodetic altitude above mean sea level (AMSL) is zero, of course!
10) Select whichever mode of latitude/longitude notation you prefer, then enter your coordinates. Winfrog or the bridge is a good place to locate this information.
11) The results are then calculated. For our tool configuration purposes you should make a note of F (total field in nanoTesla; you can safely round to the nearest 500) and Dip. You might also make a note of the individual magnetic field vectors X, Y and Z for occasional comparison with the raw data from the tool.
12) Follow the onscreen prompts to quit or calculate more values.
Appendix 2: guidelines for “suspicious” tool readings
- Tool motion indications: these will be flagged by the non-optional gravity checks in the precalculation phase.
- Absurdly high or low magnetic field readings: readings thousands of nT above the values for the location (derived in Step 1.i above) may indicate that the tool is either faulty or may not be centered in the non-magnetic collar. Low values are probably from faulty magnetometers inside the tool.
- Excessive variation of calculated results within a time window for orientation:
- Manually scan the file above and below the supposed time period for more consistent results. The time window you were given may be incorrect (typos/transcription errors in the times).
- Tool rotated during orientation period.
- Low battery voltages may cause bad measurements.
- We have occasionally seen “rifling” when apparently good tool results do not apply correctly to all or some sections of the recovered core. This can happen if the tool is stationary and got good results, but the actual core barrel twisted when fired into the sediment. Remember, orientation is performed before the core is shot, not afterwards.
Appendix 3: Disabling the tools in case of explosives work on the rigfloor
If there is any question or concern that the radio-frequency transmissions (433MHz, one of two internationally-permitted frequencies for short range radio control) involved with configuring or downloading the Flexit tools may pose a risk to the rigging of explosives for blowing pipe, then do the following:
- Keep the Flexit tools inside their brass pressure cases with the aluminum end caps installed. This should block any communication with the tools from the computer. For absolute certainty, remove the tools’ batteries as well. (TO CHECK: does battery-removal blow the memory buffer of survey data??)
- Remove the TransIT PC adapter from the computer’s serial or USB port and remove its 9V battery. Be sure you get all Flexit-enabled computers with adapters, there may be up to three of them.