A large prize could be won on the UK Continental Shelf through increasing well intervention rates and deploying new technologies. Elaine Maslin reports
Doing more with existing wells is the mantra of operators in the North Sea in the post-price crash environment. If the assumed rate of production decline on the UK Continental Shelf (UKCS) could be halved, it could add 3 billion boe of production by 2035, and help recover up to around 15 billion boe by 2050, according to Ross Dornan, lead business advisor at Oil & Gas UK, a trade association.
These sound like large numbers, but getting more out of existing assets is becoming a more attractive target in a lower oil price environment and the suite of tools with which to do it is increasing.
Increasing output from existing wells and technology innovation are the focus of Oil & Gas UK’s Reservoir and Wells Optimisation Task Group.
While drilling new production wells seems the obvious way to increase production rates, getting more from existing wells also presents an opportunity, Dornan said. Around 30% of the current UK well stock is shut-in. While some of this is for valid reasons, the reasons for all are unclear, he said.
Meanwhile, in 2016, the well intervention rate was just 10% (or interventions once every 10 years per well), despite an 82% technical success rate and low cost of US$3 per boe added.
In 2016, 405 interventions were performed (7% in subsea wells), according to Oil & Gas UK figures, at a cost of US$274 million. This added 93 million boe to production. However, 68% of the interventions were for production safeguarding, despite this work accounting for just 24% of the contribution to production from the total well intervention work carried out.
Production optimisation work, at 11% of the interventions, accounted for 33% of the total cost, with 22% of the total contribution to production. Output restoration was 23% of the well intervention work, at 48% of the cost, and made up 54% of the contribution to production, according to Oil & Gas UK’s data.
The Reservoir and Wells Optimisation Task Group has set a target of adding 200 million boe in incremental production by 2021, by restoring shut-in wells, reducing well losses and further optimising producing wells. This would contribute to a 3-4% arrest in output decline, without the addition of new fields, compared to the 6-7% base line, Dornan noted.
Rather than just promoting well intervention as a whole, however, the group is first focusing on identifying and ranking opportunities and then on the potential use of fracturing and stimulation technologies. The challenges are both increasing intervention rates and giving the supply chain more information about what the opportunities are. “We know intervention rates are low, at 10% a year,” Dornan said. “There’s generally poor line of sight on the opportunities” and operators struggle to justify the work, he added.
The group is aiming to develop cost-saving ideas for fracturing and stimulation technology and operations. It was due to draw up best practice guidelines for identifying and ranking opportunities by the end of 2017, and produce a roadmap on savings for fracturing and stimulation, and new technology development, by the end of Q1 2018. The group also intends to work with the Southern North Sea special interest group, which has been looking at use of fracturing technologies in the southern gas basin, around tight gas.
The Reservoir and Wells Optimisation Task Group also wants to quantify the 2017 annual lost opportunity by the end of Q1 2018, to highlight the missed potential. Part of this work will be revamping and adding to the benchmarking system developed by the Well Intervention Excellence Network (WIEN), a group set up a number of years ago among operators.
Until recently, data input into the WIEN benchmark was voluntary, with 12-15 operators participating. Now, more basin-wide data must be given to the Oil and Gas Authority (OGA) as part of its stewardship survey, which will help to build the benchmark.
Looking to technology
Well interventions can be performed from fixed facilities (platforms), rigs and light well intervention vessels and riserless light well intervention vessels. The trend towards use of vessels instead of rigs has been driven by a desire to lower the cost of operations, although low rig rates in recent years have reduced demand for vessel-based intervention units. Indeed, earlier this year an order for a newbuild well intervention vessel was terminated.
However, the range of well intervention tools and techniques available to operators is expanding. The well intervention world is dominated by a number of core established technologies, including coiled tubing, which allows fluids to be transported downhole, and wireline, in the form of slickline and e-line system.
Wireline systems take up less deck space, but cannot perform the heavier tasks performed by coiled tubing. E-line, or electric line, is a powered conveyance system, which means the tools it conveys downhole can receive power (such as well tractors, which can “tractor” tools further down a well than if the tool was just being deployed using gravity). Slickline is used to intervene mechanically or with self-powered tools.
E-line is a braided cable containing a conductor, requires grease injection, and causes relatively high friction with the well bore. Slickline, meanwhile, is a single strand of wire, which makes pressure control easier, such as using a stuffing box, does not need grease and can be used to for mechanical work including jarring.
New conveyance systems are now being developed to offer the benefits of both, such as semi-stiff carbon fiber reinforced polymer rods, which contain a high-power electrical conductor. These can be pushed further downhole than slickline and e-line, while still supplying power, and are able to carry heavier tools. They also have simpler pressure control equipment, with no need for grease.
Another alternative is a small diameter hose, bridging wireline and coiled tubing capabilities. This means less equipment and deck space is needed than a traditional coiled tubing operation, but fluids can be transported through the hose to an area in the well requiring a treatment (such as an acid stimulation operation). Both these new types of system – carbon-fibre rods and coil hose – can be deployed from light well intervention vessels.