Blow-Out

The blow-out

The blow-out consists in large quantities of water accompanied by a very limited amount of gas. It is a gaseous water flow. This indicates that the amount of gas that was available, in an abnormally pressured sand layer to initiate the kick, is gone. The continuing water flow is due to a positive differential pressure existing between its layer source and a normal hydrostatic regime. The gas that started to kick and the present gaseous water may not be coming from the same sand.

The origin of the concerned water layer over pressure is most probably natural; it is therefore very likely that such flow may continue for a long time if not forever.

This gaseous water flow does not present any HSE hazard. The amount of gas released is very limited: the risk to a fisherman staying on the axis of well is negligible. The water itself is clean. It is not loaded with silts and do not look like a mud. There are no sheens. Altogether, it should not have any harmful effect on the environment.

Remedial actions on the flow and on the crater

Relief well - The water is probably coming from a shallow sand layer and probably 100% from the shallowest being at 245 m. It is almost impossible to achieve a relief well targeting this depth.

Capping – The Well conductor pipe and diverter have sunk in the mud beneath the main crater. There are no capping possibilities at all.

Crater back filling - The initial blow-out managed its way in & around the conductor pipe thus causing the formation of a crater. This crater is cone shaped. It has a diameter of 40 to 60 m and a depth of 18 to 20 m. The soils below and, to a certain extend, around the crater were disturbed at the blow-out initial stages. Back filling this crater with any kind of material, in an effort to (i) stop or reduce the flow, or (ii) re-equilibrate the soils around, is not realistic. Adding weights on disturbed soils may even lead to a worse situation.

It is therefore not recommended to implement any remedial action on the well and on the crater.

Remedial actions on the Well structures

The soils around the crater have a tendency to slough-in. This causes a reduction in their capacity to sustain the weights of the fixed structures anchored into them. The effect is even more notable as such structures are close to the edge of the crater. As a consequence these structures subside. Particularly concerned are the other wells, their platforms and the gangway connecting them to the GTS itself.

The only way to stop this subsidence is to anchor such concerned structures deeper in an undisturbed soil so that any further reduction of the upper disturbed soils bearing capacity may not be of any effect. This can be achieved by an additional piling.

Situation monitoring

There is a lack of meaningful and reliable data pertaining to the follow-up of the situation that developed following the blow-out. Particularly the subsidence was not recorded during a year and a half, the flow rate (estimated at its initial stage) was not measured until now, fluids samples were not taken and not analysed…

This situation should not continue: It is important to document the evolution of the critical parameters that allow a quantified follow-up of the blow-out. Plot versus time may then be established and trends may eventually be derived. Particularly concerned are (i) the main crater and secondary vents shape and volume, (ii) the water flow rate, (iii) the subsidence and (iv) the aspect of the flow and the physical / chemical properties of the water & gas. It is one of the duties devoted to the Owner task Force to perform the QA / QC of this monitoring.