Shallow gas is one of the most dangerous incidents in well control because you don’t have the BOP set to be able to control the well. Additionally, shallow gas always happens at the shallow depth as surface hole section where you will have a difficulty to control the well. This footage below show you how serious of the shallow gas in an offshore environment.
Sedco 700 Shallow Gas Blow Out 6 June 2009
Additional details about shallow hazards that you need to know.
The shallow hazard is a formation that has the possibility to flow to surface without BOP set to control the well. It can be both water and gas kick and it can be happened at any locations as land drilling, shallow offshore environment and floating operations.
Water Flow as Shallow Hazard
The water shallow hazard is caused by natural or induced overpressure zone(s). Artesian flow, for example, is an overlaying of water sand at a higher elevation which creates a hydrostatic pressure into the lower elevation. What’s more, in the brown fields where water injections are utilized to enhance the production will have higher possibility to have the shallow water kick more than the green fields. In offshore environment, you may see this issue between 200 to 2000 ft below mud line.
Shallow Gas Hazard
The shallow gas is an unexpected gas bearing zone encountered before the rig can set the BOP. It can be extremely prolific like the footage showed before. It is relatively uncommon occurrence in the land drilling operation because at the top section, the formations are more consolidated with less permeability. The land operation will have less possibility to see the shallow gas than the offshore environment. The offshore environment will have higher chance to encounter the shallow gas because the shallow section deposits reef and vuggy limestone that can contain gas.