A kick is generally recognised by an instantaneous increase in the rate of mud returns and/or an associated gain in mud volume in the active mud tanks. A flowline show (gas cut or fluid contaminated mud) does not necessarily mean that the well is kicking.

Flowline shows can be:

• drilled shows;
• swabbed shows;
• high pressure - low volume shows.
• gas cut mud

1 Drilled shows

When drilling permeable formation, some of the fluids contained in the pores of the cuttings will enter the mud.

A drilled show is characterised by:

·gas cut or oil/water contaminated mud at the flowline when bottoms up occurs;
·no immediate pit level rise (in the case of gas, a minor rise will occur later when the gas approaches the surface)..

Gas will expand to many times its original volume when pressure is reduced to atmospheric at the surface, irrespective of the density of mud in use. Gas-cut mud will appear at the flowline. This type of contamination should last aproximately the time required to drill the permeable formation at the same circulation rate, and results in a minor reduction in the hydrostatic bottom hole pressure. If the overbalance is small, it is very important to keep the weight reduction to a minimum to avoid the well to become underbalanced.

When a drilled show occurs, it is not necessary to increase the mud density. The weight should be closely monitored and degassing is required to prevent the amount of gas to increase with each successive circulation.

2 Swabbed shows

This type of show results from the temporary reduction in hydrostatic head of the mud column, when pulling the drillstring (while making connections, or during a trip).

Swabbed shows are characterised by:

·gas cut or oil/water contaminated mud at the flowline when bottoms up occurs;
·no immediate pit level rise (in the case of gas, a minor rise will occur later when the gas approaches the surface).

A swabbed show provides a useful indicator that the overbalance may be too low, or that there may be a need to adjust the mud rheology.

3 High pressure - low volume shows

This type of show occurs when drilling (or tripping) in highly pressure/ low permeability formations and are characterised by:

·gas cut or oil/water contaminated mud at the flowline when bottoms-up occurs;
·no immediate pit level rise (in the case of gas, a minor rise will occur later when the gas approaches the surface).

Whilst drilling with an underbalanced mud, the hydrostatic pressure of the mud column plus the annular friction losses can be sufficient to contain the formation pore pressure. However, the hydrostatic pressure of the mud column by itself may not be sufficient to prevent fluid entry into the well bore.

When mud circulation is interrupted, a low volume seepage influx might enter the well. The longer the pump is off, the greater will be the influx volume.

If the pore pressure is higher than the hydrostatic pressure of the mud column plus the friction losses, formation fluid may enter the hole continuously, but at a rate so low that the moving mud column is not significantly contaminated and drilling can continue. Hole stability problems (e.g. sloughing, torque, etc.) may also give an associated indication of this pressure imbalance.

To prevent such an inflow, a substantial increase in mud density may be necessary. This will decrease the penetration rate. The underbalanced condition must be recognised and crews alerted in case a formation with a higher permeability is encountered.

4 Gas cut mud

Gas cutting of the mud will often occur when circulation has stopped for a considerable period of time (e.g. after logging, a roundtrip, etc.). This situation is not normally considered dangerous if the mud readily returns to its normal weight immediately after having circulated bottoms up. Increasing the mud weight to prevent this type of gas cutting is unnecessary and expensive if a normal overbalance of 1400-2750 kPa (200-400 psi) is used, because the reduction in bottom hole pressure due to gas cutting is generally small. However, when the overbalance is small (usually in tophole drilling operations), it is very important to minimise the reduction in BHP in order to avoid the well to become underbalanced.

Gas cut mud can also occur continuously while drilling as a result of gas which is present in the drilled cuttings. Increasing the mud weight does not stop the gas cutting effect. To confirm that gas cutting is caused by the cuttings only, drilling should be stopped and the well should be circulated bottoms up. If gas cutting does not reduce or cease after bottoms up, a potential kick condition may exist and the mud weight should be increased.

The following steps should be carried out in case of gas cutting while drilling:

·Stop circulating and make a flowcheck. If the well flows, proceed as for a kick while drilling.
·If the well does not flow, circulate bottoms up and de-gas the mud.
·If gas cutting ceases after bottoms up, continue drilling whilst de-gassing the mud continuously. Ensure that the mud which is pumped downhole has the correct mud weight.
·If gas cutting does not cease after circulating bottoms up, the mud weight should be increased by 0.1-0.25 kPa/m (0.005-0.01 psi/ft) per circulation until gas cutting has stopped, unless the formation is of the high pressure/low permeability type.