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BP drilling dual multilaterals at S pad, trilaterals possible Main OA and OB sands the initial target, but overlying N sand thicker than expected in some areas; company has first N sand horizontal well in production Kristen Nelson PNA Editor-in-Chief
Artificial lift exclusively by jet pump, long horizontal producers and water flood by dual injectors are characteristics of the Schrader Bluff formation S pad development at Milne Point field that BP Exploration (Alaska) Inc. started bringing online Sept. 1.
The S pad area, David Jenkins, BP Exploration (Alaska)’s viscous oil team leader, told PNA Oct. 2, “is the highest quality oil area at Milne Point in the Schrader Bluff” shallow viscous formation — in the 20-21 American Petroleum Institute gravity range.
“Schrader Bluff crude has several nice properties that the refiners like,” Jenkins said.
One thing they like about it is its weight. Most of the refineries taking North Slope crude oil were designed for it, he said, and the blend has been getting lighter with oil from fields like Alpine, where the API gravity is about 40 degrees. Because the overall blend going down the pipeline has gotten lighter, “some of these refiners have gone to other sources to bring in more viscous crudes to bring it back into spec.”
Increasing the viscous blend in the pipeline “actually will improve things at the refineries.”
Schrader Bluff also has a lower percentage of heavy metals which can cause problems for refiners, and a lower sulfur content. “So by comparison on the North Slope: Prudhoe Bay crude is very good — low metals, low sulfur. Kuparuk has some sulfur and metals. And Schrader Bluff is actually in between those two.”
Pushing the limits of shallow ERD BP expects to reach out 10,000 feet around S pad to drill Schrader Bluff targets. BP has “actually … been pushing the limits of what we call shallow ERD drilling, which is extended reach drilling … pushing the envelopes of what that distance is away from pads for these types of (shallow) depths.”
Nabors Alaska Drilling Inc. began drilling the vertical seismic program at S pad early this year, Jenkins said, and Doyon Drilling Inc. has drilled the majority of the wells.
“Doyon Drilling has done a fantastic job setting new performance records: drilling days per 10,000 feet and days per completion,” Jenkins said.
“They’ve moved from strength to strength: where at one well they set a record, then the next well they beat the record (and) the next well they beat that record.
“And what’s what this year’s story for drilling … at S pad has been: it’s been moving from one broken record to the next on drilling performance.”
In addition to improving productivity with long horizontal multilateral wells, “we’ve also been proving concepts at Milne Point about how these long horizontal wells can flow without expensive sand control,” Jenkins said. The wells are completed with slotted liner, “basically a normal pipe completion that has just long slots cut into it.”
This has kept costs down compared to sand-control completions, Jenkins said. From what they’ve seen so far, he said, it doesn’t look like sand production is going to be a problem in the OA and OB sands in a five to 10 year time frame, “and from what we’re seeing — what the well is telling us — we predict that in the long term they won’t have a problem with sand control.”
N sand production also possible The target for Schrader Bluff development at S pad is the OA and OB sands. Jenkins said there are some possible deeper Kuparuk targets.
On the western side of the development BP has found the N sand, which lies above the OA and OB sands, is thicker than expected.
“And so we are adding the N sand development to this project and in order to do that, last month we completed drilling our very first N sand horizontal well.”
The N sands typically have heavier oils, Jenkins said, because they are shallower and the formation is also completely unconsolidated, “so whereas in the OA and OB sands we’ve been able to get away with inexpensive slotted liner completions, we have to go to full sand control” in the N sand.
“And what we’ve been doing is working on ways to install sand control equipment less expensively,” Jenkins said. They’ve had some success already, he said: “The first N sand lateral was a lot cheaper than we expected.”
And the N sand is also more permeable than the OA and OB sands — the pore spaces are better connected — so it flows more readily.
The first N sand horizontal well came on with about a 30 percent water cut, but at more than 1,200 barrels a day.
“So that’s a very promising development which will add reserves to the S pad project.”
The thicker N sand on the western side of S pad could be developed with trilateral wells — one completion in each of the OA, OB and N sands — or individual wells could be used to reach the N sand.
Drilling through 2003 Jenkins said BP will drill through the end of October, maybe into November, at S pad and then take a drilling break until the end of the year.
“And then we’ll start drilling again in January and we’ll drill through most of the year.”
The initial well count is in the range of 14 producers and 21 injectors, and with the addition of N sand development there could be some changes, but he said he thought the final total would be somewhere in the range of the original numbers.
Water flood control BP is also taking an innovative approach to water flood at S pad, using dual injectors to give it control over which zone is flooded, instead of perforating injectors into multiple zones.
In areas at S pad without the N sand, BP is running two sets of tubing into injectors, with reservoirs separated by packers. “So we can, from the surface, directly control injection into the OB versus injection into the OA,” Jenkins said, providing control over each zone.
In areas with the N zone, BP is working with a supplier of long-life metal control valves that would allow zonal control from a single set of tubing. The technology is under development, Jenkins said, and probably won’t be available until next year.
The dual injectors are already being installed in areas without the N sand.
“And that’s become our strategy at maximizing reserves. In a typical water flood if water comes out the wrong place, you shut that zone off and then produce out of the other zones. And when water comes out in the wrong place you shut that zone off. You sort of play with the producers. And you work them over all the time trying to optimize the well production.”
But because BP is using open-hole completions, “we don’t have completions in place: we just have this long slotted liner basically holding the sand open. There’s not a lot you can do if water breaks through one area first.”
“And so our strategy for this is to control from the injector.”
That allows BP to “minimize the cost of the producers while still retaining full control of the water flood,” he said.
Reservoir given best chance Because the performance characteristics of viscous wells are different than those of other wells it will take a while for S pad production to stabilize.
“Viscous oil wells in these thin sands… actually lose about two-thirds of their overall productivity in the first three to six months,” Jenkins said.
The stabilized 1,000 barrel per day well, he said, is “really the end-game piece, that’s after it’s all stabilized out.”
The wells are now in the high steep initial decline period — and the pad is running with about half its artificial lift (see Part 1 of this story in PNA’s Oct. 6 issue).
“And so we’re actually still in a period of waiting to see what the reservoir’s going to tell us.” Jenkins said the way the S pad area is being developed — with long horizontal wells, jet pumps for assisted lift and slotted liner completions — is designed to maximize production of the viscous oil.
“We’ve given this reservoir absolutely the best chance and now what we have to do is listen and see and watch. And see what it will tell us. And the reservoir is going to tell us how much of viscous oil is going to be developable with current technology.”
How much of West Sak. How much of Polaris and Orion at Prudhoe Bay. And at what kind of rates.
“Now that we’ve got a full multilateral development under way, now we will watch and learn: and that’s where we are at the moment.”
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