GA Drilling’s unique non-contact PLASMABIT system offers a new, rig-less technology for section milling, which could change the way operators approach P&A
The costs of decommissioning are hard to face with oil at $100 per barrel, but at $60 and below they are painful. Despite exposure to this looming issue, many operators have not yet prepared a strategy. Asset retirement is still being planned around existing technology, rather than innovations – many of which could alter the outlook dramatically.
As seen earlier in this issue, by far the greatest outlay for decommissioning lies in well plug and abandonment (P&A), a process which represents about 40% of total costs.
Onshore this remains fairly cheap; costs may run from a few hundred dollars to around $100,000. Offshore however, is a different story.
Oil & Gas UK forecasts that P&A on the UKCS is expected to cost around £4.5 billion before 2022 – over twice as much topside removal, at £2.1 bn.
Low oil prices can make this worse, as operators are more reluctant to commit funds. But whether the industry wants to acknowledge the problem now or not, the inbound P&A storm can be tackled with new equipment and a fresh approach. Most of all, operators also want more certainty on how much P&A will cost.
Most wells are plugged at the lowest possible cost, in line with minimum requirements set by local regulators. However, correctly plugging a well limits the risk of costs later down the line, reducing the potential for fluid or gas leakage. In this sense, operators can see that the ROI on decommissioning lies with the knowledge that the well is abandoned safely, without threat to their future operations.
So far, the industry has been reliant on mechanical and rotary technologies to do this. In P&A, the well tubing is pulled and part of the casing is either pulled or section milled in order to install a permanent plug. Currently, the production tree and tubing must also be removed, one of the most time-consuming processes of the whole P&A operation.
Section milling – the process of removing the steel and cement casing– is one area where gains can be made. A recurring problem is that the traditional methods of section milling are time-consuming, unreliable and generate problematic swarf.
Rotary contact milling also has a tendency to need multiple fishing jobs – retrieving lost or stuck equipment down-hole. Furthermore, during well-cleaning jobs – pumping fluid down hole to remove particles and swarf – the milled material can interfere with the blow out preventer (BOP), and large particles can flow around the well, damaging it and other equipment.
Since 2013, GA Drilling has led a joint industry project (JIP) to develop PLASMABIT – a milling tool for P&A. Instead of a conventional rotary contact drill, PLASMABIT generates heatflow using an electrical arc, spinning at up to 800 rotations per second (48,000 rpm).
Aside from the electrical arc, there are no mechanically moving components in the bit. The extreme temperature (up to around 5,700°C) of the directed thermal electric plasma arc melts and disintegrates metals, rocks and cement, all without direct contact. Meanwhile, temperatures outside of the arc stay at a more manageable temperature, easily resisted by the wolframium-copper composite stricture. This directed heat makes PLASMABIT particularly effective for well interventions and section milling.
PLASMABIT melts steel and cement rapidly, enabling a higher rate of penetration (ROP) when drilling and milling. Non-contact milling also means PLASMABIT is reliable; no wear and tear on a mechanical tool limits the cost of damaged equipment, stuck tools and makes the need for tripping virtually redundant. The result, GA Drilling claims, is significantly more uptime and a cost saving to operators.
PLASMABIT can operate continuously, limited only by the lifetime of the system’s electrodes. These are designed to run for tens – potentially up to hundreds – of hours, meaning milling can proceed almost uninterrupted.
In the past, offshore P&A has usually required a rig. PLASMABIT is designed for use with coiled tubing system – saving space and the logistical problems of larger equipment. This means it can also be deployed from a light well intervention vessel (LWIV), again reducing the need for larger, heavier, machinery, and reducing costs by around 50-60% when compared with the day rate of a rig.
The system requires a power capacity of around 250 kW, provided via power cables in the tubing and well within the range available to intervention vessels. The use of coiled tubing also means that sensors within the system can provide real-time data acquisition of milled material, providing the control centre with detailed information its on composition.
Furthermore, section milling with PLASMABIT produces small particles of material, rather than swarf. This helps to ensure the integrity of the BOP and other components, limiting failures and damage caused by flyaway material. Coupled with the lower frequency of stuck tools and the smaller size of cutting produced, this offers increased safety, lowering overall reported accident rates and giving operators an additional edge when competing for contracts.
PLASMABIT is designed to compliment existing equipment and infrastructure, but remains smaller and lighter than conventional alternatives and requires fewer personnel to operate. Meanwhile, operations can be controlled remotely from a command centre.
A recent report for a decommissioning operation in the UKCS – Tullow’s Orwell wet gas field – pegged P&A time at 12 months. Accounting for the availability of suitable heavy equipment, vessels and rigs – even in a possible future environment where these are more freely available than now– adds to the lead time of a project.
Surveys of PLASMABIT JIP members suggested that almost 80% of time spent on P&A jobs relates to casing removal and preparing the well for plugging. Milling using PLASMABIT could accelerate this process dramatically.
PLASMABIT is also able to work via subsea production trees and tubing, again saving time when completing their removal operations. Moreover, this approach protects the existing assets and enables the shift from permanent to temporary P&A.
The included table (see table) highlights particular areas in which the use of PLASMABIT can speed up the process, including current operations which are rendered unnecessary.
Although still at the pre-commercialisation stage, GA Drilling hopes that overall, from planning to execution, PLASMABIT could lower the cost of the P&A process by up to 50%.
Ready to go
Major operators and service companies from Western Europe, the Middle East and US are already involved in the PLASMABIT JIP. But GA Drilling is still looking to engage more companies in order to speed up commercialisation and deployment.
The company has successfully undertaken both casing and cement removal with the PLASMABIT milling technique in water. To date, a prototype has milled one layer of a cement casing structure, and work is now underway to expand this to a second layer of casing.
Currently, PLASMABIT has reached level 3 in the API 17N Technology Readiness Level (TRL) index, where the functionality has been demonstrated through testing over a limited range of operating conditions. With a prototype now manufactured, the current target is for the project to reach level 4 – Full-scale prototype built and technology qualified through testing in intended environment– by the end of 2016. Full commercialisation would then follow in 2017.
Despite low prices exerting pressure on R&D budgets worldwide, the opportunity to speed and streamline P&A could provide some much-needed reassurance for companies concerned with the costs of decommissioning.