A kick occurs when the hydrostatic pressure of the mud column in the well is less than the formation pressure provided that the formation has the ability to produce. A kick is a positive indicator that formation fluid is entering the wellbore and Secondary Well Control must be initiated.
Recognising a Kick While Drilling
Since a rig's fluid system is a closed system, and increase in returns detected by a flow monitoring system will also be indicated by a gain in pit level. Detecting a change in pit level may be done by visual observation. This means placing some type of pit level marker in the tank, then posting someone to keep a constant watch. From your own experience, you know that to keep a constant watch on the pit level is next to impossible. This is especially true during trips, when most kicks occur. A more accurate and reliable method is to use any of the several pit level measuring instruments with the recorder mounted at the driller's console and supported by the mud logger's monitoring system. This allows a constant watch on the pit level by the driller, both while tripping and drilling. Good communication between crew members is essential on the rig. Drillers should make sure crew hands notify them if they do anything to change the level in the pits. If crew hands are adding volume to the pits, they should also notify the driller when they stop adding volume.
When drilling a formation containing gas, a minor pit level rise will be noted because of the core volume of gas being drilled. However, this will occur only as the gas nears the surface, and is due to the drilled gas expanding and is not necessarily an indication that the well is underbalanced. The timing of the increase in pit volume is important in distinguishing between a true kick and gas expansion only. The hole will also take the same volume of fluid that it gave up, after the gas bubble has reached the surface. However, if there is any question as to the cause of the pit gain, stop the pump and check the well for flow.
On trips, the drill crew should be able to recognise a 5-barrel kick or less. During drilling, the crews are generally able to recognise a 10 barrel kick or less.
The size or severity of a kick depends on the volume of foreign fluid allowed to enter the wellbore, which depends on the degree of underbalance, the formation permeability, and the length of time it takes the drilling crew to detect that the well is kicking.
SECTION 3 : KICK INDICATORS
Recognising a Kick While Tripping
Trip tanks are recognised to be the safest and most reliable method of monitoring mud volumes on trips. It is recommended that a continuous hole fill up be used when tripping out of the hole. When tripping in the hole the, trip tank should be used to ensure the correct mud displacement is taking place.
Rig movement with a floating drilling rig makes it more difficult to recognise kick indicators while drilling or tripping. For this reason additional fluid volume detection equipment is installed in the mud pits to compensation for rig motion. It is recommended for floating drilling units that flow checks be performed on the trip tank with the hole fill pump circulating across the bell nipple to eliminate rig motion as much as possible.
Situations that can mask a kick:-
Mud weight adjustments while drilling. Mud transfers while drilling. Partial lost circulation.
Solids control equipment and degassing mud. Spills and leaks in surface equipment. Drain back.
Pump start up and shut down.
SECTION 3 : KICK INDICATORS
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