This article presents a pre-survey checklist & running procedure for conventional multi-shots magnetic survey tools:

Pre-survey Checklist

MMSs are normally run by a Survey Engineer. The pre-survey checklist for MMS instruments is similar to the pre-survey checklist of MSS. In addition to the MSS pre-survey checklist, it should be ensured that the Survey Engineer has been supplied with the well status, including:

Driller's pipe tally, interval to be surveyed, distances between stations and depth reference (e.g. rotary table)

Hole size and last casing depth

Maximum bottom hole temperature

Mud weight and viscosity

Wellhead co-ordinates

Target azimuth (Grid or True North)

Tie-in station survey data and co-ordinates

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

Elevation from the common reference datum of:

-rotary table

-top of casing head housing (bottom flange)

-top of cellar

-mudline suspension

-sea bed

Grid convergence and declination.

Running procedure

1.Load the film into the camera section (this is normally done by the Suco at their base).

2.Assemble the camera, battery pack and timer. Set the time interval between pictures. Check the correct operation of the timer and bulbs. Check that the film is advancing.

3.Select and attach the required inclination and compass unit.

4.Start the instrument timer and synchronise it with the surface watch. Record the time on the field data sheet.

5.Mount the instrument in the instrument barrel and drop the assembly into the drillstring (see alternative running procedures below). Allow sufficient time for the assembly to fall and land on the landing ring. In high angle holes the instrument can be pumped down slowly.

6.When the instrument has landed on the landing ring, hold the drillstring stationary for a sufficient length of time to allow a survey photograph to be taken (preferably 2 photographs at each station).

7.Trip out the drillstring and record on the field data sheet, the depth and time of each stand. Hold the drillstring stationary after each stand pulled for a sufficient length of time to allow at least one photograph to be taken.

8.After the survey interval has been covered, trip out the bit as far as the casing shoe and recover the survey instrument with an overshot run on a wireline. Alternatively trip the bit to the surface and recover the instrument.

9.When the instrument is recovered, develop the film and allow it to dry before reading.

10.In high angle holes the instrument can be inserted into a NMDC at the surface. This allows records to be taken as the drillstring is lowered into the hole. Although this method is not often used, it allows a check to be made while coming out of the hole. However, the instrument tends to be in the hole too long and in hot boreholes the heat shield is only good for a few hours, after which the film will be burnt.

11.The instrument can be run in open hole on a wireline (but if the hole is washed out there may be difficulties in getting good survey data).