Written by Intetech’s Dr Liane Smith
The recent approval of shale gas extraction by ministers in the UK means that operations are now planned to start in 2015. Shale gas has the potential to make a significant contribution to ensuring energy security and reduce the UK’s reliance on imports.
But while business leaders are enthusiastic about shale gas and its potential to boost industry and keep energy costs down, environmentalists are more cautious. The extraction process entails hydraulic fracturing (fracking), which has proved controversial. Incidents in the US have seen fracking associated with pollution of water through the chemicals involved, while the UK Government imposed a moratorium on the practice 18 months ago after the UK’s first fracking site was found to have caused two minor earthquakes.
Well integrity the highest priority
The UK Government’s Chief Scientific Adviser, Sir John Beddington FRS, asked the Royal Society and the Royal Academy of Engineering to review the scientific and engineering evidence and consider whether the risks associated with fracking as a means of extracting shale gas could be managed effectively in the UK.
Published in June 2012, the review concluded that the health, safety, and environmental risks can be managed effectively, and that the risk of fractures propagating to reach overlying aquifers is very low. It also concluded that more likely causes of possible contamination include faulty wells. Well integrity was therefore identified as being the highest priority, with robust monitoring also considered vital before, during and after shale gas operations.
Managing well integrity is therefore much more than simply ensuring safety during a current activity or specific scenarios, rather it concerns the sustainability of the equipment to operate safely for the full design life of the well. Well integrity management systems exist both at a documentation and software level, and combine key well operating and production data within a framework for decision-making, management processes and organisational structure.
The shale gas opportunity
Because the shale gas sector is still young, it can learn much from the conventional oil and gas business in terms of best practice, but firms also have the opportunity to take the initiative on well integrity management, given that conventional players are only just beginning to implement more systemised approaches. Well Integrity Management System (WIMS) documentation sets the standard in terms of helping to set out and establish an approach for all aspects of well life – from design and construction, to operation and abandonment – and for all well types.
However, much of the information relating to well production, barrier equipment and design is held in different departments in various formats and under different timelines. Not only do these ‘silos’ make it difficult for senior executives and management teams to collate, compare and report on well integrity data, but the length of time this can take impacts on their ability to identify problem wells, make informed decisions and take remedial action.
A systemised approach
When a shale gas well is drilled, the well bore is protected by a steel casing, with the space between the steel casing and the rock wall in the well bore filled with cement. Known as a ‘cement sheath’, the protection of this sheath is essential in order to prevent contamination.
The normal deterioration mechanisms are to be expected – namely temperature and pressure fluctuations due to changes in production rates. These can cause potential degradation of the cement bond between the casing and the cement, or the well bore and the cement.
Additionally, the fracking process itself is unique, in that a large volume of high-pressure fluid is being pumped into the well bore for prolonged periods, stressing all the cement bonds, or any kind of mechanical or integral seal within the well. Given the potential for a loss of integrity over time, the cement sheath and surface conditions must be monitored continuously. The operator must also ensure vigorous fluid quality monitoring. Shale gas requires large amounts of water, if the water needs to be reused during the process then the quality of the water must be assured.
An advanced well integrity management system provides the ability to analyse, compare and validate all operating well data, alert and report on exceptions and make information available throughout the enterprise to the right people at the right time. It provides:
Production information – to confirm that all fluids in the well are within their safe operating limits for flow rates, pressures and temperatures
Barrier tests – to check that safety-critical equipment is leak-free
Well design data –to support informed well workover plans
Well history – to track all actions on the well and handover events
Practical steps for shale gas
The performance of shale gas wells should be monitored as per conventional wells in order to detect signs of leaks at an early stage. This ensures that action can be taken to control them in a timely way, rather than waiting until any aquifer has become contaminated or other problems.
Operators also need to monitor fluid compositions at the wells and in surrounding aquifer monitoring wells to reassure the public of diligence and quality control of their potable water. There are three crucial steps to this process: sample the well data, record that data and ensure control mechanisms that keep operations within defined safe operating envelopes.
To date, there has been too much focus on the fracking process, and not enough on managing the integrity of the completed wells themselves. With all departments and risk areas integrated into a single, highly-functional well integrity management system, operators can have access to a single version of the truth that translates into usable information for proactive decision-making. More importantly, by taking the lead on well integrity, shale gas operators will not only ensure integrity is established and maintained effectively, but can be seen to be doing so by both regulators and the general public.
Image sourced via danielfoster437