Pre-survey checklist & Running procedures for conventional magnetic single-shot survey tools:
MSS tools are normally run by the Driller. The pre-survey checklist and running procedures are given below.
Check that the instrument box is complete and that the angle units have been checked in the workshop before delivery to the wellsite. Check that no angle unit has been used more than 25 times after calibration.
Check that the kit box includes:
1.two angle units of each range, which should be used alternately;
2.batteries specified for the instrument;
3.film discs;
4.developing chemicals.
Ensure that the film is kept dry before the survey is run.
- unit is chosen having an angular range which corresponds to the maximum expected inclination of the borehole.
- Check whether the instrument is to be top or bottom landed, or used with a mule shoe.
- instrument landing assembly will seat correctly in the landing ring (TOTCO ring), and will not jam or land eccentrically.
- landing ring in the proper place when making up the BHA.
- instrument will pass the rest of the BHA above the landing ring and not hang up (e.g. in the jar).
- pressure and temperature ratings on equipment are within expected values. Consider using a heat shield or heat sink, but check that the instrument will still pass through the BHA.
- required length of NMDC is available.
- Find out and record the optimum position of the compass within the NMDCs, i.e. minimum magnetic influence from the rest of the drill string, and space out the instrument accordingly. If two compasses are run in tandem, the bottom compass should be at the optimum position.
- sinker bars if the mud is heavy and viscous and/or at high inclinations.
- Before surveying always circulate sufficient mud to avoid a back flow of cuttings into the BHA.
- Obtain grid convergence and current declination data.
Magnetic single-shot survey tools - Running procedures
1.Assemble the camera, battery pack and timer. Check the correct operation of the timer and bulbs.
2.Select and attach the required angle unit to the camera, battery pack and timer.
3.Estimate the survey time. If the activating mechanism is a timer, set the required time lapse and set the surface watch to read the same time lapse. The time lapse should equal the sum of the times required to:
-mount the instrument in the barrel;
-run the instrument through the drillstring;
-provide a safety margin of a few minutes (3-5 minutes) in case of any delays.
-As a general rule of thumb allow 1 minute per 100 m (300 ft) when running the tool on a wireline. For the first survey to be run in a well an extra time safety margin should be used. The times required for subsequent surveys can be more accurately estimated from previous runs.
4.Load the film disc into the camera section.
5.Assemble the lower section of the pressure barrel (including mule shoe when required for drillstring orientation).
6.When ready to take the survey, simultaneously start the timer and surface watch.
7.Fit the instrument inside the pressure barrel. Assemble upper and lower parts of the pressure barrel.
8.Run in hole through the drillstring until it is landed on the landing ring.
9.Due to the adverse effects of shock loading, the most favourable method for running the MSS is to run it on a wireline. However, if appropriate shock absorbers are used in the instrument barrel and on the instrument assembly, the MSS can be dropped into the drillstring and retrieved at the surface. If dropped, it can also be retrieved with a wireline overshot at the survey depth or after pulling the BHA into the casing shoe.
10.Stop drillstring movement just before surface watch indicates that the survey will be taken. Make sure that the drillstring is stationary while the survey is being made (include a time safety margin).
11.Recover the barrel and remove the instrument.
12.Develop the film disc and allow it to dry. Read the inclination, magnetic azimuth and toolface from the disc. Record all survey information including depth, azimuth, inclination, toolface, compass spacing and serial number of the angle unit on the disc envelope, see Section 7.4. Place disc in envelope after it has been independently checked by at least two people.
13.Reject the survey if the film is unreadable. If the survey readings are suspect, consider rejecting the survey.
14.When using a motion sensor the instrument will take a photograph if it is held up (i.e. stuck) for any reason. This photograph may be taken when the instrument is not in the NMDC section.
15.If the monel sensor becomes hung up in the steel section of the drillpipe it will not take a photograph. It will however take a picture 30 seconds after entering the NMDC section even if the instrument or drillstring is still moving.
On some units the compass card is presented as a mirror image. In such units the relative positions of high-side and toolface are reversed. When reading the disc use the instructions and magnifying reader specified for the particular angle unit.