This article describes the surveying guidelines for wells with potential well control problems.
Magnetic Single Shot / MWD
In Exploration, Appraisal or Development well hole sections, where mobile hydrocarbons are present or potential well control problems could be encountered, regularly spaced Magnetic Single Shot(MSS) (or MWD ) surveys shall be taken at a frequency not to exceed 500 ft. When drilling deviated wells, this frequency shall be increased to a minimum of every 100 ft during build (more if the Directional Driller needs them), turn or drop sections regardless of the presence of hydrocarbons or potential well control problems.
Well Control
In the upper hole sections there is no risk of a blowout and an inclination of 4° is exceptional, therefore the surveying requirements can be relaxed from the above requirements until the intermediate casing is set.
In the hole sections where BOP’s are installed, it is expected to encounter hydrocarbons with the associated risk of a well control problem and therefore an implicit blowout potential. Prior to entering these hydrocarbons a Magnetic Multi-Shot (MMS) is required in the previous hole sections such that the position of the previous casing shoe is known to an acceptable accuracy.
In these hole sections single shots should be taken to provide the required accuracy to be able to intercept the wellbore with a relief well.
Additional Surveys
Additional multi-shot surveys shall be taken in the following circumstances:
- Gyro Single Shot (GSS) surveys shall be taken when drilling hole sections where magnetic interference is detected. For surface and intermediate sections, run an MMS, if no reading, run casing and then run a Gyro Single Shot. For production section, magnetic interference is determined by wireline logging N12 (Dip Meter Log)
- Gyro Multi-Shot surveys (GMS) shall be taken to decrease positional uncertainty prior to drilling critical hole sections (e.g. high pressure sections, critical wellbore proximity hole sections). In this instance the requirements for the GMS will be clearly stated in the Drilling Programme.