Trident fishbones
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BlueCrest triple fishbones equal reservoir contact of 21-27 individual wells
Steve Sutherlin Petroleum News
BlueCrest Alaska has unveiled its new “trident fishbone” well design, building on the company’s successful fishbone design oil wells, which have markedly improved the economics of BlueCrest’s Cosmopolitan project targeting the Hansen field offshore Cook Inlet. As the name implies, the trident configuration involves the drilling of three fishbone wells from one single wellbore.
“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 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 wells to be drilled in a shorter 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 BlueCrest’s original fishbone concept, a complex formation of wellbores drilled through the rock provides one long horizontal “mainbore” 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, then into the long reach well to the surface.
It will take approximately four months to drill each trident fishbone well from spud to production, Johnson said.
Development at Cosmopolitan will proceed more rapidly due to the trident fishbone well.
“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 well possibilities 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 is drilling oil deposits under Cook Inlet from an onshore surface location about three miles away, a distance rendering scores of wellbores to be 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 fallen over time, the company said.
BlueCrest confirmed that 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, BlueCrest conceived of, and was able to execute, the fishbone approach.
Production headed upward As it looks forward to drilling its first trident fishbone well, BlueCrest has enjoyed a year over year production increase at Cosmopolitan.
Production data reported by the Alaska Oil and Gas Conservation Commission said BlueCrest’s Hansen field averaged 1,469 barrels of oil per day in June - the most recent month reported, down 14.2%, 244 bpd, from a May average of 1,713, but up 83.4% from a June 2018 average of 801 bpd. BlueCrest had two wells in production in June 2018 and five wells in production in June.
The advent of the trident fishbone well is likely to hasten the production growth curve.
The total combined thickness of the Cosmopolitan oil sands is more than 1,000 feet.
Like many oilfields, Cosmopolitan oil is deposited between the grains of sand in underground geological layers stacked on top of each other The 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.
Unconventional location 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 utilizing long extended reach wells drilled from onshore.
BlueCrest said hydraulic fracturing was conducted in two of its initial Cosmopolitan wells, but the cost of the fracturing process was very high and the small fractures were inefficient at creating vertical flow paths between the stacked layers.
The fishbone ribs in the first BlueCrest 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. The oil flows downward into the common horizontal main bore; no hydraulic fracturing is employed.
Each rib of the fishbone is equivalent to a separate well drilled from the surface, BlueCrest said.
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