Edwin done on Kashagan as no discharge of even WBM into Caspian. In general not recommnded as :
- Higher risk of sub-surface lost circulation both in magnitude and mud barrel costs.
- Higher risk of surface losses due to incorporation of excessive volumes of water wet cuttings into the system leading to water wetting of the shakers.
- Risk of bit balling and therefore complete absence of any penetration rate due to the incompatibility between an oil based mud system and extremely water wet young shale formations.
- If pump capacity is limited inadequate hole cleaning with OBM and stuck pipe much more likely than with low inhibitive WBM.