While the downturn slowed enthusiasm for new E&P projects, the industry has embraced boosting production from mature assets.
In an interview with Bloomberg at this year’s CERAWeek by IHS Markit, BP CEO Bob Dudley cheered the British supermajor’s negative decline rate, owed to increased output at its mature fields. BP isn’t alone. Shell and Statoil have also committed to maximizing production from older wells.
Service companies, such as Weatherford International (NYSE: WFT), are helping operators address the challenges presented by maturing assets and enable increased production volumes with new rigless technologies.
“From our side, what we are seeing now is a renewed focus on the mature assets across the board from both onshore and offshore,” said Keith Adams, global director of well services for Weatherford. “We estimate that 38% of the mature asset well count has some form of integrity or intervention requirement.”
Some of the key issues with mature assets today, according to Adams, are casing and tubing integrity, as well as safety valve and wellhead integrity issues.
The rising shift toward maintaining mature assets is due to remediation being more cost-effective than new drilling. Rystad’s Global Well Market Outlook reported in January 2018 that exploration drilling accounted for 3% of the wells in 2017. One of the ways Weatherford aims to lower the cost of ownership in mature fields is by deploying rigless solutions that eliminate the expense of mobilizing a workover rig.
In one example, a client in the Southern North Sea came to Weatherford to intervene on a shut-in water injector where the tubing had corroded.
“Historically, you would have to bring in a rig and work that well over to retrieve and replace the injection string,” Adams said. “We partnered with a local coiled tubing company to convey a comprehensive solution that included remedial work as well as the deployment of a 4 1/2 x 2 7/8-in. straddle system. Using our two-trip WidePak system, we deployed a straddle across the 1200-ft section of corroded tubing. This solution enabled the operator to bring that well back online as an active water injector without the need for a workover rig.”
Adams highlighted Weatherford’s Surge Frac technology, which enables pinpoint chemical stimulation across the reservoir. The technology has been used on wells in Norway, Denmark and the Middle East, according to Adams.
“Bullheading chemicals from the surface and hoping that the chemicals would get to the right place within the reservoir section was a common practice historically, and still is common in some areas,” he said. “What we’ve come up with is a multi-trip coil tubing-deployed stimulation straddle system that can selectively straddle off discrete zones that require chemical treatment — enabling multiple zones to be treated in a single trip.”
On one job in the North Sea, the Surge Frac system enabled a 37% increase in an oil-producing well. While performing an acid stimulation through a 4,117 ft (1,255 m) horizontal section, Weatherford deployed the Surge Frac system to target stimulation zone by zone. The precise selection of zones, compared to normal bullheading, significantly reduced the risk of overstimulating the well heel and under stimulating the toe, the company said.
The Surge Frac system can be set multiple times in the reservoir section on a single trip. This ability lowered project costs and saved rig time by eliminating additional downhole trips, Weatherford said.
The system stimulated 22 selected zones with 15% hydrochloric acid in a single run, the company reported. During stimulation a maximum pressure of 7,058 psi and a pump rate of 14.5 barrels per minute were reached. The Surge Frac system, Weatherford said, stimulated all targeted zones while preventing water influxes.
Adams said Surge Frac can perform memory monitoring of the stimulation pressure. Additionally, “if the coiled tubing has real-time capabilities, we can also perform real-time monitoring of the stimulation process.”
Another technology Weatherford is deploying on mature wells is an inverse gas lift system.
“With traditional gas lift wells, you pump your lift gas down the annulus and you produce up your tubing,” Adams said. “When you lose the integrity of your annulus, the well has to be shut-in.
“What we’ve devised is a system that is deployed through the existing production tubing string. Once installed, the system provides a new conduit for the lift gas. This allows you to produce hydrocarbons via the annulus between the new inner string and the existing tubing, while still maintaining a fully functional dual-flow safety valve [DFSV].”
Inverse Gas Lift
Weatherford embarked on a four-well campaign for Total’s Alwyn North Field in the North Sea, deploying its Renaissance Inverse Gas-Lift System in 4.56-in. and 5.95-in. sizing. Weatherford worked with Total to create system upgrades with improved alloys to eliminate flow erosion and corrosion issues observed with the system previously, Weatherford said.
Total required the system to be installed to assist reservoir blowdown and maximize production as well as to introduce gas lift to a well that had no gas lift capability. Total also wanted to avoid full well workover in aims of reducing operational costs.
Weatherford deployed the inverse gas lift system completion, including a DFSV and a suspension hanger on 2 3/8-in. landing string.
The work also included landing concentric hanger in a modified spool piece, pressure testing concentric hanger seals to 5,000 psi, pressure testing upper tubing to 3,500 psi, expelling the pump open plug, inflow pressure testing the DFSV, and nitrogen lift well for integrity testing prior to gas injection.
Weatherford reactivated the previously depleted wells, enhancing production from existing producers, the company said.
What Lies Ahead
To optimize the future of mature fields, Adams said service companies and operators need to continue working closely together on new technology developments that meet today’s ever-changing challenges.
“The way in which operators are now looking at mature assets, there’s definitely a renewed focus on working closely with service companies that can provide complete, end-to-end solutions,” he says. “As long as the oil price stays at current levels, it's all about extended recovery from existing fields.
“There’s no question that mature assets will remain a key focus for the foreseeable future.”