How to avoid loss of primary control:
- mud of adequate density is used;
- active volumes are sufficient and continuously monitored;
- any change in density, volume, or return flow from the well to the active mud tanks is detected immediately and prompt corrective action taken;
- swab and surge pressures are kept to a minimum.
Below are presented some signals which indicate the possibility of foreign fluid entry to the well bore:
- gas cut or contaminated fluid at the flowline (this indicates that a hydrocarbon-bearing formation has been penetrated);
- an increase in penetration rate (although this may be due to various factors, it could indicate that an overpressured formation has been penetrated. When a drilling break occurs, a flow check should be made as quickly as possible);
- an increase in salinity;
- a decrease in circulating pressure.