Award-Winning HCB™ Bulk Cuttings Transfer and Storage System Implemented in the UK North Sea
The honey comb-based HCB™ bulk cuttings containment and transfer system has been used for the first time in the UK North Sea to successfully contain oil-based mud (OBM) cuttings from the 14,000-ft 12 ¼” section. This operation was undertaken for a major operator in an effort to sustain continuous uninterrupted drilling.
After extensive onshore and offshore trials which culminated in the award of this contract, the HCB tank system was chosen to replace the traditional ship-and-skip option for OBM cuttings containment for health, safety and environmental (HSE) reasons. The system eliminates manual handling risks associated with skip movements and crane operations. The cuttings are transferred within a closed loop system further reducing the potential for an environmental incident.
The operation comprises two pneumatic blowing units that collect and transfer the OBM cuttings from the shakers to eight HCB tanks permanently located on the rig. An additional sixteen HCB tanks are installed on the supply vessel used to transport the cuttings to shore-based facilities for processing.
During the course of the drilling the 12 ¼” section, the HCB system—in combination with the SupaVacTM SV400 cuttings transportation system for cuttings transfer—kept pace with drilling rates of over 300 feet per hour with transfer rates from the rig to the supply vessel in excess of 25 tonnes per hour. During the operation the supply vessel also set a UK North Sea record by being on alongside for 72 hours during the cuttings transfer operation.
The OBM cuttings are transferred from rig to vessel via flexible interconnecting hoses. Once the vessel tanks are full the contents are taken to an onshore thermal processing plant and blown directly into a quayside facility.
The simple but unique features of the HCB tank design provide a solution to the historical problems associated with cuttings transfer and containment. The HCB tank utilises a standard silo type vessel contained within a DNV-certified frame. Internally, the tank base houses an inverted cone surrounded by six hexagonal outlet hoppers in a honey comb arrangement. This unique design feature minimises blockages or bridging of the product when the discharge cycle is activated. If the drill cuttings settle out during the storage period, each cone has numerous air injection points which when activated will agitate the cuttings into a flowable state prior to discharge. The six outlets at the base of the cones are controlled by knife valves which open and close in a cyclical manner to create a series of slugs in the discharge to line to minimise blockages.
HCB tanks prior to installation on the rig.
Discharge outlets at the base of the HCB tank.
When used in conjunction with the SupaVac cuttings transport system, the HCB tank system will allow operators to store cuttings in a fully enclosed environment on a much smaller footprint than traditional cuttings boxes, and store and discharge cuttings in various states ranging from dry powder to liquid. In addition, the HCB tank will completely discharge cuttings into a conveying line. It also will transport drill cuttings to HCB tanks on a supply boat along side the rig, from the supply boat back to the HCB tanks on a rig, and from the boat to onshore facilities for treatment and disposal.
Pneumatic Cuttings Transport System Prevents Disruption to Drilling
On a separate UK North Sea operation, the operator was faced with the prospect of shutting down drilling during a zero discharge “ship and skip” operation on a semi-submersible rig. Operational issues on the rig made it impossible to lift cutting boxes (skips) between the supply boat and rig using conventional methods.
The SupaVac system had been installed on the rig to transport drill cuttings from the solids control package to cuttings skips on deck. The SupaVac unit has the unique ability to both vacuum recover and pressure discharge drill cuttings and drilling waste to suitable skip loading locations around a rig or platform. The cuttings on this project were being gravity fed directly into the top of the unit and blown to the skips. As an alternative to shutting down drilling, the SupaVac unit was quickly reconfigured to blow the cuttings directly to skips on the supply boat. Drilling was not disrupted.
Without the SupaVac SV400 cuttings transfer system, the operator would have incurred over 10 hours of down time. At an estimated spread cost of $300,000 per day, the SupaVac cuttings transfer method resulted in a savings of $125,000.
The SupaVac cuttings collection and pumping system includes a compact, air-operated, vacuum recovery and pressure discharge pump. The system is designed to operate in hazardous locations, safely collecting and pumping materials such as drill cuttings, tank bottoms, heavy crude sludge and sand slurries. Unlike other conveyance systems, the SupaVac system can work with dry, damp or liquid materials. Because it is pneumatically operated and contains no electrics, it can be installed anywhere on location. The smaller SupaVac SV60 unit is available for handling small volumes of drilling waste and liquid recovery and transfer.
Compact SupaVac SV400 cuttings transfer unit.