Large-Scale Drill Cuttings Thermal Treatment and Slop System Retrofitted to Drillships During Zero-Discharge Drilling Operations Offshore Angola
Authors: Sharma Vaibhav , Jepson Don , Andrade e Sousa Edevaldo , Dompetelo Mpanda , Zghal Jamel , Bermudez Raul , Lonca Matthieu , Diogo Jose , Szakolczai Cyril , Rennie Paul , Donaldson Neil 
Published: February 2020

The Angolan government began transitioning to a zero-discharge policy for oilfield operations in 2014. To reduce the economic impact of this ruling, operators searched for ways to minimize waste volume and costs associated with treatment and handling.

Total E&P Angola (TEPA) set out to equip three drillships in offshore Angola, two in Block 32 and one in Block 17, with advanced technologies to streamline the waste handling process, minimize waste volume, and recover valuable fluids. The deepwater wells were expected to produce 230,000 BOPD in 2018 in Block 32 alone. The selected waste management systems would need to be reliable, efficient, and capable of being retrofitted onto each drillship.

Thermomechanical cuttings cleaner (TCC) were installed as the primary solution for the drilled solids processing. Slops treatment unit were also installed on each drillship. The TCC required ancillary equipment to comply with zero discharge constraints, including vacuum transfer systems and specialized cylindrical storage tanks for drilled cuttings.

The system was sourced from various global locations and mobilized to Angola. To conform to the zero-discharge regulation ED 97/14, the typical TCC equipment layout and operations were modified. Instead of rehydrating cuttings and flushing them overboard, dried cuttings were stored and transferred for final disposal to a landfill.

The entire installation was an extensive and complex project, from rig surveys and design concepts to the remote location logistics, equipment installation, and coordination across multiple groups across the operator, rig contractor and service provider. All components had to be installed on fully operational drilling rigs with challenging space constraints.

Each technology package was successfully installed and commissioned, and treated thousands of tons of drilled cuttings and processed thousands of cubic meters of slops with zero accidents, incidents, or nonproductive time, despite reduced processing rates that did not affect drilling operations.

Savings included recovery of base oil, decreased skip-and-ship and lifting operations, and reduced onshore slops treatments. As of Dec 2018, &gt;25,000 metric tons of drill cuttings have been processed.

Because of the zero discharge of drilling wastes, the separated solids from the TCC were rapidly cooled and stored on the drillship before bulk transfer and transport to shore. A dried solids cooler was designed and installed to reduce the 260°C (500°F) TCC output to 50°C (122°F). The dried solids coolers were the first ever implemented offshore. A new dust management system was also deployed to help control dust created by moving the ultrafine dried solids generated by the TCC's hammermill. Further, the use of efficient vacuum transport system and large-capacity cuttings storage tanks significantly reduced crane lifts that are required for standard skip-and-ship operations, thus reducing HSE risks.

Once completed, the integrated technology package was the largest of their kind globally. The success of this operation was largely attributed to the careful collaboration between the operator and service provider.