Underbalanced Drilling: General Issues
Safety in Underbalanced Drilling
Because of the large volumes of oil and gas production potential in underbalanced drilling, strict safety procedures have to be implemented during the drilling operation.
Potentially explosive and flammable hydrocarbons have to be isolated while they are produced during drilling. In onshore operations, oil is sent to storage facilities while gas is typically flared. In offshore operations, due to limited storage space available, both oil and gas are flared.
The presence of hydrogen sulfide (H2S) in produced hydrocarbons poses an extreme danger to the rig personnel. H2S is extremely poisonous and can be fatal even at very low concentrations. If the presence of H2S is anticipated during drilling, the operator must provide:
- Necessary notice of the proposed operations and hazards.
- Special training.
- An emergency contingency plan.
- H2S resistive material.
- H2S sensors, warning alarms, portable and fixed air breathing devices.
For conducting a safe underbalanced drilling operation, proper personnel training is a key issue. Having the critical manpower helps to avoid unforeseen emergencies.
Storage and flaring equipment have to be properly sized according to the anticipated volume of hydrocarbon production. Wind direction should also be taken into consideration while positioning the flare system and the storage facilities.
Since the presence of air can cause a corrosive downhole environment, explosions and downhole fires, extreme care must be exercised to avoid combustible mixtures.
In order to control the back flow from drillpipe, at least two drillstring floats should be installed on the drill string assembly. Depending on the type of the underbalanced drilling fluid used, more floats may be needed for maximum control and safety.
BOP stacks should be designed with extreme care by going through a step-by-step testing for every single system part. They should be tested when installed, once every week and following each repair.
The drilling operation should be stopped immediately if pressures exceed the maximum design limits.
