Evolving technology drives West Sak development
20 years ago this month: ConocoPhillips sextuples production, doubles length of horizontal laterals in formation at Kuparuk River
Editor's note: This story first ran in the Nov. 23, 2003, issue of Petroleum News.
Technology is driving the development of West Sak, the billions of barrels of shallow, heavy crude which overlie the deeper Kuparuk River formation at the ConocoPhillips Alaska-operated Kuparuk River field on Alaska's North Slope.
West Sak production averaged some 250 barrels a day per well when production began in 1997-98, ConocoPhillips Alaska's West Sak development coordinator, Jordan Wiess, told Petroleum News Nov. 18, 2003.
(See diagram in the online issue PDF)
That initial production was from vertical wells fractured to stimulate production.
Well designs for West Sak have evolved since then, Wiess said, beginning with short horizontal sections in the West Sak sands and extending out with longer and longer horizontal sections.
Today, he said, the company has "essentially doubled and tripled the length of the reservoir exposed in our horizontal wells from where we were in the year 2000." Today the company's West Sak wells have as much as 6,000 feet of horizontal section through the reservoir.
And production rates have changed dramatically: Today the company sees initial production rates of as much as 4,000-5,000 bpd from West Sak wells, with production leveling off in the 1,400-1,500 bpd range.
Not only are horizontal sections through the reservoir longer, Wiess said, they are multiple, with dual laterals into the major D and B sands, and plans under way for tri-lateral wells, with the third lateral in the deeper A sands.
And not all of the ideas came from within ConocoPhillips. BP is also developing heavy oil, at the Schrader Bluff formation at the Milne Point field and at Orion, a west-end Prudhoe Bay satellite.
"We've really been pushing each other to achieve the next level," Wiess said, and that has helped "create these breakthroughs in technology and it's really enhancing our developments."
Since the late 1990s, Wiess said, "the BP Schrader Bluff team and the West Sak team have really been leapfrogging each other with technologies, trying to push that limit."
Dual lateral wellsConocoPhillips has been developing the West Sak D sand and B sand, while BP, at Milne Point and Orion, has been developing the Schrader Bluff OA and OBd sands. At West Sak and Milne Point the companies have both put in "dual laterals, two long horizontals - leading to those sand bodies." At Orion, BP is planning a tri-lateral, with three legs from the same well (see illustration of proposed West Sak tri-lateral well).
ConocoPhillips has taken that idea and applied it to West Sak, where the company will look at using a tri-lateral for the D, B and A2 sands.
Wiess said ConocoPhillips has been drilling horizontal production wells at West Sak for three or four years, with wells drilled from existing Kuparuk River drill sites. The company began drilling West Sak wells from the 1D drill site in 1997, and in 2001 moved on to drill from 1C. West Sak wells are now being drilled from 1B. The 2004 program ConocoPhillips is looking at calls for drilling West Sak wells from the 1E drill site.
"We're drilling off our existing drill sites to make use of the existing infrastructure," Wiess said. Kuparuk type well spacing was 80 feet between well centers, and West Sak wells are now being drilled with 20 and 40 feet between well centers, "so we're able to slide two or three wells in between the existing Kuparuk wells on most of these well sites."
Final design state at 1J padConocoPhillips is now in the final design for West Sak drilling from the 1J pad, the old West Sak pilot pad. "We're at the stage where we're completing all of our engineering effort," Wiess said, and will be moving the project forward through the corporate and partner approval process.
The 1J West Sak development will be multi-lateral horizontal producers but will also have horizontal injectors. A step change in the last two years was to go from vertical injector wells to an undulating injection well through the B and D sands. Plans developed for the 1J project call for developing the lower A sand, as well as the B and D sands, "with a tri-lateral producer," and the well design evolved to include a tri-lateral injector well. "We'll be putting in one injection horizontal in each of the sand bodies," some 1,000 to 1,200 feet from the producers.
Infrastructure additions neededThe 1J development plan in final engineering now involves adding pipelines, power lines and on-pad facilities at the 1J pad "to develop a larger block of West Sak." Since the pad was built in the 1980s three Kuparuk reservoir wells have been drilled there and are producing. Wiess said the West Sak team was "able to make use of those wells to gather additional data in the West Sak reservoir" as the wells were drilled through the West Sak to reach the deeper Kuparuk formation.
Once the 1J West Sak development is approved, pipelines and power lines will be put in during the winter construction season, and facilities added on the pad such as the trunk and lateral system for the new wells.
Drilling will be up to 20,000 feet per well. Even though the reservoir is shallow, about 3,500 to 3,700 feet, "we're drilling down about 5,000 to 8,000 feet to get to the reservoir because we want to access as much as we possibly can from a central location, and then we drill our 6,000 feet (horizontally through the reservoir) - "
The current development plan for the 1J pad calls for 37 West Sak wells, Wiess said, 17 injection wells and 20 producers.
A mixture of horizontal wellsThe wells will be "a mixture of single horizontal wells, dual horizontal wells and then tri-lateral horizontal wells," Wiess said, depending on the sands in the area to be drilled.
The D and B sands are generally about 25 feet thick, with some 25 feet of shale in between, but the deeper A sand is broken down into a lot of thin layers, from one to 10 feet thick, spread over some 100 feet of depth.
The D and B sands are naturals for lateral wells, Wiess said, but the A sand hasn't been developed since the company stopped drilling vertical wells because it is spread out into such thin stringers.
But in 2003, "after we were able to prove we could drill these undulating injection wells, we actually went and drilled an undulating producing well through all those A sand stringers." That is in the existing West Sak producing areas.
"As we move down into the 1J area, a lot of those little thin sands (in the A sand) disappear and we end up with two main sand bodies that are five to 15 feet thick, so that's where we're going to be able to take up just a straight lateral through those sand bodies," he said. The wells each take some 30 days to drill, so with 37 wells in the plan, the 1J pad will be a large project, Wiess said.
And after 1J? That partly depends on "additional technology breakthroughs" in Canada and in Venezuela, Wiess said, "to really attack some of those more viscous, more difficult West Sak crudes that move updip into the shallower horizons."
Technology has been the driver"The main driver over the past five, six years has just been technology breakthroughs," Wiess said.
"The enhancement of horizontal drilling has been one of the key things." When ConocoPhillips began drilling horizontal wells in the West Sak formation in 2000, the company thought the technical limit for such wells was probably about 3,000 feet.
"And today we're pushing laterals out 6,000-6,500 feet.
"And we don't know where that's going to go in the future. We continue to evolve with the technology that's evolving and apply that, and we've seen tremendous gains."