Drilling Without Spills: Designing Mud-Gas Separators for a Worst Case Scenario

Ziegler, Robert F. (WEATHERFORD) | Deshpande, Kedar M. (WEATHERFORD) | Patil, Harshad P. (WEATHERFORD)

OnePetro 

Abstract Objectives/Scope

Current Well Control Procedures require "Divert Overboard" for the handling of riser gas. This rule is a consequence of the Deepwater Horizon accident, where the PRV of the Mud-Gas Separator was the source of the gas that led to the explosion and the death of 11 crew. This practice will inevitably lead to the spill of potentially thousands of barrels of oil based mud.

Methods, Procedures, Process

Current Mud Gas Separators (MGS) on a drilling rig are utilized to separate liquids from gas that are circulated out after a kick has been taken in a conventional well. The current practices, when the primary well barrier, which is the weight of the drilling mud is breached, is to shut the well on BOP (Blowout Preventers) and circulate out the volume of formation fluids (gas/oil/water) that have entered the wellbore. For the safety of the personnel and rig equipment, this kick is circulated out with closed BOP’s which divert the fluids to the rig choke that is lined up to the MGS. This prevents any formation fluids from entering the rig floor or be exposed to the rig environment. The MGS diverts the flammable gases to a vent line. Since the traditional MGS designs are open to atmosphere, the gas flowrates that enter separator have a potential to breach through the mud leg causing a separator blow through if these gas flowrates are higher than gas handling capacity of the MGS. If flow exceeds the limited MGS capacity and a blow through condition occurs, the flammable gas can disperse onto the rig. Taking the experience of Underbalanced Drilling into account, where tens of thousands of barrels of reservoir content can be produced safely in a 24h time period, the learning for separator design and multiphase medium handling are taken as a basis to design an adequate drilling system for arctic use, however in closed system drilling mode with the underbalanced capabilities the operating limit to handle unintended inflows.

Results, Observations, Conclusions

Taking the UBD experience into account, a mud gas separator design and operating procedure for spill-free arctic operations is proposed.
 This paper focuses on using CFD techniques to understand the relationship between the gas handling capacity of the MGS and the separator diameter, its internal geometry and length. The paper attempts to study separation of gas and liquids inside the separator that is open to atmosphere and the reasons that could cause separator blow-through conditions

Novel/Additive Information

For the first time, the vast knowledge on 4-phase separation in the production and UBD world is transferred to conventional drilling operations, with the objective of a closed, safe and spill free drilling system as required for the arctic.