BlueCrest Alaska has developed a new “trident fishbone” well design, the latest innovation the company has devised for efficient and economic development of its Cosmopolitan oil project offshore Cook Inlet.
Oil was discovered at Cosmopolitan by Pennzoil Oil Co. in 1967. Other companies have tried to make the project work over the years. BlueCrest knew of the challenges going in, but challenge had created an opportunity for a persistent independent operator to innovate a path to financial viability.
The trident fishbone design is built on the company’s success with its single fishbone wells, which have markedly improved the economics of Cosmopolitan.
The trident concept is the latest breakthrough to arise from a long trial and error process. That process has yielded several successful solutions, not only to the challenges inherent in the location of the reservoir - 3 miles out and 1.5 miles down from an onshore drill pad - but to other development challenges that cropped up along the way.
Three tines of the trident
As is implied by the name, the trident configuration involves the drilling of three fishbone wells into the reservoir from a single wellbore originating at the shore-based pad.
“The fishbone wells achieve significantly more reservoir contact and penetration than conventional wells, but we haven’t calculated the incremental ultimate recovery; it is substantial,” J. Benjamin Johnson, BlueCrest Energy CEO and president told Petroleum News.
“Each fishbone well contacts the same amount of reservoir rock as seven-nine individual horizontal wells, and each trident well should recover the same ultimate reserves as three fishbone wells since the reservoir contact is the same,” Johnson said, adding, “so, each trident well provides the same amount of reservoir contact as 21-27 individual wells.”
The trident fishbone allows more penetrations into the reservoir in less time, bringing new oil production online sooner, BlueCrest said in a recent presentation. “This saves substantial time and cost associated with drilling the long-reach wells from the onshore drilling location to the offshore reservoir for each fishbone.”
Under the original fishbone concept, one long horizontal “mainbore” runs along the bottom of the oil zone, from which multiple full diameter wellbores are drilled upward to penetrate individual productive oil sands.
The finished well structure resembles a fishbone, with multiple “ribs” that flow down into the mainbore.
It will take approximately four months to drill each trident fishbone well from spud to production, Johnson said.
“Each trident well saves five months to drill the wells that would reach the same reservoir penetration with just the fishbone wells,” Johnson said. “Overall, it cuts the total drilling time down by more than two years.”
Fishbone wells boost efficiency
The old school method of opening up all the productive sand members of a traditional onshore development would be to drill scores of wellbores, each penetrating all of the layers. But BlueCrest must drill so far to reach the reservoir, making scores of wells impractical and uneconomic.
With its powerful purpose commissioned directional drilling rig, BlueCrest has accurately steered paths of wells throughout the reservoirs, while setting new Cook Inlet records for long-distance drilling at Cosmopolitan.
Drilling costs have decreased over time, the company said.
BlueCrest said the Cosmopolitan reservoir rock is “highly consolidated, providing a strong capability of wellbores to remain open after the holes have been drilled through the rock.”
In addition to steering wellbores in any direction desired, BlueCrest was able to sidetrack wells to create new well paths branching off from an existing well.
After considering all these factors, the company conceived of, and was able to execute, the fishbone approach.
As it looks forward to drilling its first trident fishbone well toward the end of 2019, BlueCrest has enjoyed a year over year production increase at Cosmopolitan.
BlueCrest’s Hansen field, the Cosmopolitan project, averaged 1,371 barrels per day in July 2018, up 58.5% from a July 2018 average of 865 bpd, according to data reported by the Alaska Oil and Gas Conservation Commission.
BlueCrest had two wells in production in June 2018 and five wells in production in June 2019.
Conventional field, unconventional location
The total combined thickness of the Cosmopolitan oil sands is more than 1,000 feet.
Like many oil fields, Cosmopolitan oil is deposited between the grains of sand in underground geological layers stacked on top of each other. The Hanson field’s individual oil-filled sand layers are separated by thin horizontal layers of silt or shale that create barriers preventing the oil from moving vertically between the oil-filled sands.
BlueCrest estimates that in an old onshore basin such as West Texas, a conventional development of Cosmopolitan’s type and size of oil deposit would require more than 100 individual wells.
But Cosmopolitan’s conventional field is in an unconventional location, which has prodded the company to innovate.
Many modern wells on Alaska’s North Slope and in other basins are initially drilled downward from a surface location, then turning horizontally to pass through the reservoir, opening paths for oil to flow from sands contacted by the wellbores, BlueCrest said. Hydraulic fracturing is commonly employed to create limited paths for the oil to flow from other nearby sands into the horizontal wellbores.
But BlueCrest, over the past three years, has focused on developing a drilling and completion process that would optimally open up the multiple layers of Cosmopolitan sands to production.
BlueCrest tried hydraulic fracturing in two of its initial Cosmopolitan wells, but the cost was high and the fractures were inefficient at creating vertical flow paths between the stacked layers.
The fishbone ribs in the company’s first fishbone well penetrate the reservoir at a 110 degree angle, spaced 800 feet apart - 15 acre spacing. Each rib penetrates the entire production interval, from the Hemlock to the Starichkof. Oil flows downward into the main bore; no hydraulic fracturing is employed.
Fifth plan of development
BlueCrest’s fifth plan of development, or POD, covers the 2019 calendar year.
The company drilled the first fishbone, the H-12 well, in 2018, under its fourth plan of development covering the 2018 calendar year. The H-12 consists of a wellbore with a long horizontal tail with seven vertical laterals rising into the producing formation.
Based on evaluation of the H-12, BlueCrest re-drilled the H-16 well, with eight laterals.
In 2019, a new eight lateral fishbone well, the H-4, was drilled some 3,200 feet south of existing Cosmopolitan wells. It was brought into production in March 2019.
The H-4 tested the southern extent of the reservoir, BlueCrest told the state.
After evaluating results of the H-16a (the re-drill) and H-4 fishbone wells, BlueCrest said in the POD, it “will decide the best possible location for a possible second well in the 2019 drilling program.”
The company filed permits for and got spacing exceptions for its first Trident well, the H-13 on Feb. 22, 2019, stepping out to the northwest. It will be drilled in fourth quarter 2019.
Tapping a separate gas field
BlueCrest is making plans to tap into the Cosmopolitan unit’s 5,000-foot-thick natural gas dome above the Hansen field oil accumulation.
“We are seriously studying it right now,” Johnson told Petroleum News in a May 2019 interview that included BlueCrest Alaska Operating LLC President John M. Martineck.
“This gas field is not related to the oil; it is a separate field lying directly above the oil but not connected to it,” Johnson said.
The natural gas in the dome is too shallow to be accessed from onshore drilling.
“We discovered the gas field in 2013,” Johnson said, the year BlueCrest and its former partner Buccaneer Energy drilled the Cosmopolitan 1 vertical well with the Endeavour jack-up rig. (BlueCrest bought out Buccaneer in 2014 and took over as operator.)
“We logged it, cored it and flow tested it,” Johnson said. “In addition, we have very high resolution 3D seismic and we can see each one of the major zones, see the structure. We can see any faults and there are none in the field except for the fault at the north of the field and at the south end of the field.”
Martineck said the company has “confirmed the 3D seismic with all the wells we’ve drilled. We can see the gas sands are continuous. We know it is a large field … and with no water.”
The Ninilchik gas field to the north is very similar to BlueCrest’s gas field: “We’d be producing from the same horizon, the Tyonek,” Johnson said, noting “most other inlet gas fields are produced from the shallower Beluga and Sterling formations.”
A pair of the Tyonek sands tested at Cosmopolitan 1 flowed at 7.2 million and 7.3 million cubic feet per day with no water, Buccaneer said at the time.
The conventional development scenario in Cook Inlet has been offshore platforms, but BlueCrest is considering development using a jack-up rig and subsea completions.
“We are still looking at putting in a single platform but modern technology is leading us to look at subsea completions,” Martineck said. “It would be a very clean, very simple system ... and this particular location in Alaska would be very well suited” to it.
The gas would be transported by a “3-mile pipeline from the wells to our surface location,” Johnson said. “We’re already set up for gas in our facility. We’d have to make some changes to our onshore facility, but they’d be minor.”
Pool rules request
BlueCrest submitted an initial field and pool rules application to AOGCC Aug. 2 for the Hansen oil pool at its Cosmopolitan field.
An important aspect of pool rules is oil well spacing, proposed as Rule 3, allowing for no well spacing restrictions within the oil pool, accommodating horizontal, multilateral and fishbone style wells, with the exception that no well can be completed within 500 feet of the exterior boundary of the unit unless ownership is the same on both sides of the unit boundary.
In its proposed rules BlueCrest notes that “fishbone multilateral wells will be completed barefoot with no liners or screens in the reservoir section.”
The company said its multilateral fishbone well design has spacing between the individual fishbones, laterals, in a single well and laterals in adjacent wells of some 800 feet, which would require seven or more spacing exceptions per fishbone. To produce remaining reserves under current well spacing rules would be an unnecessary administrative burden on BlueCrest and AOGCC, the company said.
BlueCrest said the proposed pool rules would eliminate intra-pool spacing rules and allow it “to target smaller, undrained portions of the pool that cannot be reached/contacted by wells conforming to current statewide spacing restrictions. Elimination of all spacing requirements inside the pool will help to maximize recovery from otherwise bypassed pay, while allowing for continued production from established development wells.”
“The Hemlock/Starichkof reservoir is compartmentalized and highly stratified,” the company said, with very limited communication between wells.
