As you know well control is very important subject in drilling industry and in order to understand it clearly, you need to understand basic principle. This time we would like to share this excellent VDO showing the basic pressure control of drilling process. It is just only five minutes but it will give you details plus illustration for more understanding. Additionally, we also add full VDO transcript for anyone who cannot catch the VDO content.
This is the VDO transcript from our team.
Fluids in a formation are under pressure. When drilled, this pressure can escape to the surface if it is not controlled. Normally, drilling mud offsets formation pressure, that is the weight or pressure of the drilling mud keeps fluids in the formation from coming to the surface.
For several reasons however, the mud weight can become lighter than is necessary to offset the pressure in the formation. When this situation occurs, formation fluid enters the hole. When formation fluids enter the hole, this is called a “kick”.
A blowout preventer stack is used to keep formation fluids from coming to the surface. These are called BOP’s. By closing off a hole in this equipment the rig crew can seal off the hole. Sealing the hole prevents more formation fluid from entering the hole. With the well sealed or shut-in, the well is under control.
Rig crews was you was a service BOP system on land rigs, jack up rigs, submersible rigs and platform rigs. They use a sub-sea BOP system on off shore floating rigs like semi-submersibles and drill ships.
A blowout is dangerous. Formation fluids like gas and oil rise to the surface and burn. Blowouts can injure or kill destroy the rigs or the environment. Rig crews therefore train and work hard to prevent blowouts. Usually they are successful, so blow outs are rare but when they happen they spectacular and thus often make the news.
A kick is the entry of formation fluids into the well bore while drilling. Kick occurs when the pressure exerted by the drilling mud is less than the pressure in the formation of the drill string is penetrating. The mud that circulates down the drill string and up the hole is the first line of defense against kicks. Drilling mud creates additional pressure as it circulates. The mud pressure keeps the formation pressure from entering the well bore. On the rig, it is said that the mud keeps the well from kicking.
Sometimes however crew members may accidentally allow the mud level or the weight in the hole to drop. This drop in weight or level can happen for several reasons. For example the crew may fail to keep the hole full of mud, may pull the pipe out of it or they may pull the pipe tool fast which can lower the bottom hole in pressure. When the mud level or at the mud weight drops the pressure exerted on the formation decreases. If either happens formation fluids can enter the hole. If they do the well takes a “kick.”
In other words when the formation weight exceeds the pressure of the mud column then the well can kick. To keep a kick from becoming a blowout the rig crew uses blowout prevention equipment.