Any special requirements for coring fluids shall be included in the Drilling Programme. The general requirements are described below:
- The mud gradient shall exert an overbalance over the formation pressure of no less than 200 psi.
- The static fluid loss shall be less than 8 cc.
- The viscosity and yield point shall be as low as possible to reduce core erosion.
- The solids content shall be as low as possible to prevent core contamination.
- The mud filtrate salinity and composition shall be as close as possible to that of the formation water.
- Water-based mud shall be properly deoxygenated with an oxygen scavenger.
- No surfactants shall be used in the mud.
- The mud shall be conditioned before pulling out for coring. Any mud losses shall be controlled. LCM shall not be pumped through a core barrel unless absolutely necessary.
- During coringthe mud properties shall not be changed unless absolutely necessary. If changes are to be made to the properties the changes shall be made slowly. There shall be sufficient volume of spare mud which can be added to the system to control the mud properties.