This article presents pre-survey checklist and running procedure for conventional gyro survey.

Pre-wellbore survey checklist

• Before starting to drill a new well and before every new wellbore survey, ensure that there is a foresight (directional reference) and that the direction from the wellhead has been determined by the Topographic Department.
• Ensure that the wellbore survey Engineer is using the correct foresight. Sometimes there is more than one foresight in use at the same location.
• Ensure that the wellbore survey Engineer has been supplied with the well status, including:

1.For multi-shots the interval to be surveyed and distance between stations and depth reference (e.g. rotary table). For single-shots, the position and type of landing ring or orienting sub.

2.Casing, liner, tubing, drillpipe size and weight and any restrictions thereto.

3.Maximum bottom hole temperature.

4.Mud weight and viscosity.

5.Wellhead co-ordinates.

6.Target azimuth (Grid or True North).

7.Reference point (foresight and direction; Grid or True North).

8.For in-hole oriented multi-shots, all previous wellbore survey data.

9.Elevation from the common reference datum of:

-rotary table;

-top of casing head housing (bottom flange);

-top of cellar;

-sea bed.

10.Maximum expected inclination and intervals where the dogleg severity is expected to exceed 1°/10 m (3°/100 ft).

11.Principal hole azimuth.

12.Tie-in station wellbore survey data and co-ordinates.

13.Grid convergence.

• When wellbore surveying any production well, consult Production Department (wireline section) for lubricator, BOP requirements and safety procedures.
• It is the responsibility of the Survey Engineer to check the following:
  • Pressure and temperature ratings. If the temperature limit is exceeded. use a heat shield, or ensure that the hole is circulated to cold mud or to make the wellbore survey in multiple runs.
  • If pressure rating is exceeded, only to survey down to this limiting depth.
  • The availability of a line wiper to wipe mud off the wireline.
  • The availability of centralisers with correct size and stiffness according to casing or liner size(s) and expected inclination.
  • When using gyro single or multi-shot for orienting check whether the mule shoe stinger will fit into the orienting sub and alignment is correct.
  • The selected gyro spin axis orientation for the gyroscope type against principal hole azimuth and expected maximum inclination.

Typical running procedures

Gyro single and multi-shot (GSS and GMS) surveys are always run by Survey Engineers. They can be run in cased hole or drillpipe. The running procedures for single and multi-shot are included here for the reference of Opco personnel..

The running procedures given not only differ by single or multi-shot but also in the use of a cage device for mechanical foresight alignment.

Film-type gyro single-shot with caging

1.Prior to the wellbore survey, run the gyro for a time in a warm-up stand. This is to check for correct running after shipment, and to allow the gyro to reach a steady state temperature.

2.Assemble the gyro battery pack and battery packer section of the lower pressure barrel.

3.Check the voltage and current from the battery section. If these are below the specified levels, fit new batteries.

4.Fit centralisers and sinker bars to upper and lower pressure barrels if required.

5.Suspend the lower pressure barrel on the landing plate, which should be placed on top of the drillpipe. Fit the sighting telescope to the lower pressure barrel.

6.Place the caged gyro on the battery packer.

7.Hang the top pressure barrel on wireline over the hole.

8.Sight on the foresight, see Fig. 1255.

9.Uncage the gyro.

10.Run the gyro for a minimum of 5 min. Check the drift rate (this should be less than 10 (°/hr)).

11.Recage the gyro.

12.Assemble the timer, camera battery pack, camera and angle unit.

13.Wind the surface watch and set the timer (required run time plus a safety margin of 1 min/100 m (1 min per 300 ft), plus 5 min extra for the first run). Synchronise the timer and surface watChapter Check that the camera lens gate is closed and load the single-shot disc.

14.Fit the angle unit, camera, timer and camera battery pack onto the gyro. Open the lens gate. Sight on the foresight. Simultaneously start the timer, surface watch and uncage the gyro.

15.Remove the sighting telescope.

16.Lower and fit the upper pressure barrel.

17.Pick up the tool, remove the landing plate. Zero the wireline counter with the gyroscope level with the top of the rotary table.

18.Run in hole. If running to bottom ensure tool is seated in the mule shoe or landing ring.

19.Wait until the surface watch indicates that the wellbore survey has been taken; allow a 2 min. safety margin. Pull completely out of the hole.

20.Check if the mule shoe 'tattle tail' indicates that the tool was seated correctly if applicable.

21.Put the tool back on the landing plate. Remove the upper pressure barrel. Fit the telescope and close the lens gate. Remove all the instruments except the gyro. Sight on the foresight and read the observed drift on the gyro compass card, and the elapsed time on the surface watch Write the results on the field worksheet. Note that the elapsed time on the surface watch should not exceed 15 min.

22.Leave the gyro running and cover with a plastic bag while developing and reading the disk. This reduces time if a rerun is required.

Film-type gyro multi-shot without caging device

1.Prior to the wellbore survey, run the gyro for a time in a warm-up stand. This is to check for correct running after shipment and to allow the gyro to reach a steady state temperature. If the GMS is run to orient the drillstring, align the mule shoe stinger to the gyro locating pin (which is aligned to the tool face pointer, well in advance of surveying, as discussed in Section 16.4.2).

2.Assemble the gyro battery pack and battery packer section of the lower pressure barrel. Fit new batteries.

3.Fit centralisers (and sinker bars if required) to upper and lower pressure barrels. Suspend the lower pressure barrel from the landing table located over the rotary table.

4.Check the voltage and current from the gyro battery pack. If these are below the specified levels, fit new batteries.

5.Hang the upper pressure barrel from the wireline above the landing table in preparation for the final assembly.

6.Mount the gyro on the battery pack.

7.Fit the sighting telescope to the tool face reference mark. Align the gyro with the tool case reference mark. (This is done automatically with the Baker Hughes Inteq LRG). Sperry-Sun use an alidade mounted on top of the gyro, see Fig. 1255. By aligning both the alidade and telescope to the foresight, the gyro is aligned to the tool case. Tighten the set screws, locking the gyro in place.

8.Run the gyro for 10 min to warm up and then take a 5 min drift check. Drift rate should be less than 10°/hr.

9.Assemble the angle unit, camera, timer and camera battery pack. Check the correct operation of the timer and bulbs. Check that the film is advancing.

10.Align the telescope on the foresight and orient to the pre-selected gyro spin axis orientation.

11.Start the timer and synchronise with the surface watChapter Record the initial orientation on the wellbore survey company field data sheet.

12.Fit the angle unit, camera, timer and camera battery pack on top of the gyro.

13.Lower the upper section of the pressure barrel, fit it to the lower section and tighten.

14.Realign on the foresight using the telescope. Take a 5 min drift check with the tool aligned to the foresight (held in the landing table). Note that the first picture is the gyro orientation when aligned to the foresight (start case).

15.Pick up the tool, remove the landing table. Zero the wireline counter with the gyroscope level with the top of the rotary table.

16.Run in hole to the first wellbore survey station. Note depth and time on field data sheet. Use the surface watch to see when the picture has been taken. Commence running to next wellbore survey station and note time.

-when using a minute timer, hold the instrument stationary at each wellbore survey station for a sufficient length of time to allow at least one photograph to be taken after the tool has settled;

-when using a 20 second timer, hold the instrument stationary for at least 45 seconds to allow at least two photographs to be taken.

17.Continue taking wellbore surveys at the specified survey stations.

18.After each 10 minutes of wellbore survey time for the LRG or 15 minutes of survey time for the TSG, hold the instrument stationary at a survey station for a 5 minute drift check.

19.When total depth has been reached, pull out of the hole; continue to take drift checks as before, and out-run surveys every 100-150 m (300-500 ft). The out-run survey intervals chosen should allow at least 4 wellbore surveys to be made on the out-run. These should coincide with in-run survey stations.

20.When the tool is back on surface, check and record wireline depth counter reading as the gyroscope passes the rotary table. Set tool in the landing table, fit the telescope and realign on the foresight while the camera takes a picture of the final gyro orientation (end case).

21.If misalignment correction is required, take cluster shots, see also Section 15.4.

22.Remove the upper pressure barrel, angle unit, camera, timer and camera battery pack. Realign on the foresight and observe the final gyro orientation. Record the time and values on the field sheet.

23.Remove the camera from the instrument section.

24.Develop the film.

Surface read-out gyro tools Running procedure

1.Make up the tool on the catwalk with the appropriate centralisers. Connect to the wireline.

2.Warm up the system prior to running the wellbore survey.

3.Place the tool in the landing cable over the well. Clamp on the telescope and align it to the foresight.

4.Enter the foresight azimuth into the surface computer. Orient the gyro in the general direction of the hole azimuth using the surface computer.

5.Once the gyro is aligned, take a drift check. Pick up tool on wireline. Remove landing cable. Zero depth counter with gyro sensor at rotary table level.

6.Survey on the way in at 25 m (or 100 ft) stations with a drift check for every 10 minutes. The frequency of these checks should be increased if there are severe doglegs.

7.On the outrun take wellbore surveys at regular intervals, 100 m (300 ft) or less.

8.When the tool returns to the surface, check wireline depth counter. Replace landing table on rotary and hang-off tool. Refit the telescope and realign the gyro to the foresight. Measure the observed drift. The unclosed or closed survey results can then be presented.