Thermal process versus ‘skip and ship’
There is a perception that mobilising thermal processing equipment offshore on a one-well basis would entail high installation costs and involve installation and demobilising around other drilling related activities. However, following a thorough evaluation of both methods, AGR found significant HSE and operational benefits:
- a reduction in skip handling.
- a reduction in waste handling.
- reduced weather exposure, i.e. limiting movement of skips on deck and to a dedicated vessel.
- a reduction in the requirement for crane use.
- no requirement for a dedicated vessel to be at the rig site during drilling.
- the ability to re-use base oil in the drilling fluid at source.
AGR also undertook a commercial evaluation. Considering the reduction in time waiting on weather, removing the dedicated vessel requirement, and the reduction in logistics costs, it found that, even with the increased rental and mobilisation costs, the overall costs could be 36% lower.
Reduced risk, cost and harm to the environment
Despite reduced crane availability, due to weather and other rig mobilisation requirements, the offshore thermal processing package was fully installed within nine days, half a day ahead of schedule.
As space was limited on the Ocean Guardian, the thermal processing equipment configuration and layout design was the most compact installation performed to date. Having all the equipment within the same area in a smaller footprint allowed TWMA to achieve the most efficient processing.
More than 1,600MT Mt drill cuttings were processed from the three sections of the Orlando development well: equivalent to 300 skips. This meant:
- a total of 1255.19Mt of recovered solids were diverted from landfill and discharged overboard with an average total petroleum hydrocarbon organics (TPH) of 0.058%, well below the North Sea allowable discharge of <1%.
- a total of 223.37 m3 of recovered water was discharged overboard with an average oil on water of 2 ppm, also well below the North Sea allowable discharge of <30 ppm.
By processing drill cuttings offshore at source, it was estimated that approximately 26 hours of weather downtime was removed during drilling operations, which would have resulted in an associated spread rate cost of approximately US$380 000.
Consequently, this allowed continuous drilling during adverse weather conditions. It also significantly lowered handling, storage, offshore lifting and ‘skip and ship’ vessel requirements, saving an estimated US$640 000 in vessel costs alone (based on the market rates at that time). Having the package onboard also gave the client flexibility leading to compressed schedules.
In addition, the solution minimised the HSE risks associated with the unloading and offloading of 300 skips, including more than 3000 associated crane lifts, at the rig site, quayside and ultimately, the processing facility.
The drilling waste management operation was completed within time and on budget with zero Lost Time Incidents and zero loss of containment to the environment during operations.
The offshore thermal desorption unit performs at processing speeds of up to 10 tph in even the harshest offshore environments and reduces heavy labour lifting operations by up to 95%. Compared with the traditional ‘skip and ship’ method, it also delivers significant cost savings of up to 40% per well. Most notably, it can cut carbon footprint by more than half.
The first single well operation on the Orlando field has proven that onsite thermal processing can safely increase operational efficiency, support well cost reduction initiatives, exceed regulatory requirements and mitigate the likelihood of safety and environmental incidents.
TWMA has since secured five offshore processing contracts with the TCC RotoMill in the UKCS total more than US$20 million. These awards demonstrate the markets outlook at utilising offshore thermal processing technology and further validates the value this technology brings to our client’s operation both in safety, operationally and commercially.
This is part two of a two-part article. Part one is available to read here: https://www.oilfieldtechnology.com/offshore-and-subsea/06022020/optimising-financial-and-environmental-gains-with-at-source-drilling-waste-management-part-one/.
Read the article online at: https://www.oilfieldtechnology.com/drilling-and-production/07022020/optimising-financial-and-environmental-gains-with-at-source-drilling-waste-management-part-two/