Definition - What does Shallow Gas mean?
Shallow Gas is natural gas which has accumulated at a very shallow depth from the earth's surface. Shallow gas cannot be controlled while drilling, it can only be diverted from the wellbore; therefore, drilling engineers have to be careful not to encounter a shallow gas accumulation area. Also the timing of the crew’s reaction to act is very low due to its shallow depth, and at times before diversion equipment is activated, the gas flows to the surface and the rig floor leading to a potentially risky situation.
Petropedia explains Shallow Gas
In usual conditions when there are no drilling activities taking place in an oil well, shallow gas bearing zones are normally pressurized. When drilling is ongoing, the pore pressure of the rocks increases due to the change in the gas gradient and this in turn leads to un-equilibrium when the drill bits hit the shallow gas bearing zones.
During the preparation of the well drilling plan and site survey procedures, it is advisable to first identify and avoid the shallow gas bearing zones as they can be risky to the drilling team and rig infrastructure. When the drilling team encounters a shallow gas zone they quickly move to divert the gas from the wellbore with the help of diversion equipment.