Shallow Gas - Planning Guidelines
Shallow gas is defined as any hydrocarbon-bearing zone which may be encountered at a depth close to the surface or mudline. Generally it is not possible to close-in and contain a gas influx from a shallow zone because weak formation integrity may lead to breakdown and broaching to surface / mudline.
This situation is particularly hazardous when drilling from a fixed installation or jack-up.
Shallow gas-bearing zones are usually normally pressured. However, the effective increase in pore pressure due to gas gradient can lead to underbalance when a . . .