Electronic Magnetic Multi-Shots (EMMS) are a definitive multi-shot surveying instruments. However, MWD data may be accepted as the definitive survey provided QA/QC results are within the acceptable criteria.

They have the advantage of being relatively insensitive to compass spacing, less mechanical parts, more options for time setting and quality control outputs.

Running Guidelines

During Electronic Magnetic Multi-Shots surveys:

• the instrument assembly should be run in the bottom NMDC or in the collar immediately above the MWD tool (if run)
• the tool should be run centralised
• a 6 - 10in extension tube should be welded to the TOTCO ring to prevent flip over and should be positioned to ensure the survey barrel is as short as possible within the compass spacing constraints
• the top instrument should be spaced out 6 ft below the drill collar box end, if tandem probes are run
• the Survey Engineer shall determine the data logging rate of the tool based upon the likely duration of the survey
• rotation shots shall be taken.

The Survey Engineer will correct the readings for instrument bias based on information obtained from rotation shots. This involves setting the slips to keep the instrument at a fixed depth and recording surveys at a certain number of different tool face settings.

The normal instrument configuration of EMMS surveys is single stack (one instrument).