Recognising a kick and need for immediate action.A kick occurs when the hydrostatic pressure of the mud column in the well is less than the pore pressure of a producing formation.Drilling breaks and gas, salt water, or oil contaminated mud at the flowline are potential signals. A kick however indicate that formation fluid is entering the well bore. The volume of the kick depend upon: the degree of underbalance, the formation permeability and the length of time the formation is allowed to remain underbalanced.

Need for immediate action

When a well kicks, it should be closed in immediately. Reaction time is critical. Equipment shall be suitable and crews trained to detect immediately small changes in active fluid volume. Drills on the proper method of closing the well shall be repeated so it can be done quickly and without mistakes.

The decision t0oclose the well shall be the responsibility of the driller.

Increased mud returns are not always conclusive evidence that the well is kicking. However, always have a flow check and if necessary, DO NOT HESITATE TO CLOSE THE WELL IN.

Underbalanced symptoms in overpressured formations may be caused by the plastic behaviour of shales in the overbalanced mode (ballooning). Ballooning cn be manifested by:

·initial high gas shows from recently drilled sand layers, regardless of their much lower original natural pressures;

·initial loss of mud when circulation is started, followed by an equivalent gain of mud after circulation is stopped;

·SIDPP equal to the ECD effect on BHP, immediately after circulation is stopped and the well is closed-in;

·high penetration rates with very low WOB.

Genuine symptoms of underbalance may also be caused by nearby wells which have been drilled with a large overbalance. Sidetracked holes often behave quite differently from the original hole for the same reason.

Reducing or stopping the ballooning effect is probably best achieved by bleeding off pre-existing charged shales as drilling progresses, sticking close to the natural pore pressures of the formation. It will result in temporary shows and brittle sloughings.

Drilling with oil based mud (OBM)

OBM can dissolve large quantities of hydrocarbon gases, CO2, and H2S. A gas kick in OBM initially behaves like a water kick with spontaneous expansion of the gas close to surface when the dissolved gas comes out of solution (bubble point).

The most important aspect, when drilling with OBM, is to be aware of the unpredictable behaviour of gas expansion near surface, especially when circulating bottoms up after a roundtrip or any circulation after long static periods, because gas may have entered the well before circulation started. Drilling crews have to be made aware of this problem.

Standard well killing procedures apply for OBM. However, gas present in gas cut OBM may be difficult to remove completely due to the solubility of gas in OBM.

If presence of dissolved gas in OBM is suspected and it is expected to cause splash problems at surface, the well may be closed-in prior to reaching bottoms-up, after which circulation can be completed via the choke manifold.

Wells drilled with a subsea BOP stack need to be closed-in before the suspected influx has reached the BOP's.