Friday, September 16, 2011

BP sees good results with Ugnu heavy oil production test

Tim Bradner
Alaska Journal of Commerce

Nabors Alaska Drilling Co. prepares to drill a heavy oil test well for BP on the North Slope in this file photo. The companies involved have seen good results so far from the efforts.


The first of four test production wells drilled by BP into the large Ugnu heavy oil deposit on the North Slope is performing well. This is significant because unconventional resources like heavy oil could make a major contribution to future North Slope production, but producing companies have to first figure out whether this oil, which is thick and lower quality, can be even produced.

BP’s first test well was encouraging. The well produced up to 650 barrels per day of oil mixed with sand and with the sand removed the net production was about 550 barrels per day, said Eric West, BP’s manager on the project. Production at the first test well began on April 22.

“It was higher than we expected. It is a good well,” West said.

The Ugnu has huge in-place heavy oil resources with estimates as high as 23 billion barrels of oil in place in the reservoir, but BP and other producers have worked for several years on ways of producing the oil, which is very thick is consistency.

The pilot production program underway now is testing two different production techniques with four wells that are also drilled to different spots in the reservoir to assess how differing reservoir conditions will affect production, West said.

“We want to be very careful that we don’t make a judgment based on the performance of one well drilled to a certain part of the reservoir, a false positive,” West said.

A key difference between these tests and heavy oil production technologies used in places like California, where steam is injected, is that BP is hoping to produce Ugnu oil with a cold production process that avoids warming of the permafrost layer that extends to about 2,000 feet under most of the North Slope.

The Ugnu test wells were drilled at S Pad in the Milne Point field. The first well brought on line, designated S-41, is a conventional horizontal production well that works with a progressive cavity pump, West said. The pump creates suction in the well that pulls the oil and sand mixture out of the formation and up the well, West said. The sand, along with solution gas, is separated at the surface.

The first well produced more sand than was expected in a horizontal well, with as much as 20 percent of what came up the well being sand. Learning from this, BP will make changes in the screens installed in the horizontal well that are intended to minimize the sand flowing into the well.

The second well to be brought on line is a “CHOPS” (Cold Heavy Oil with Sand) a well type developed in Canada to produce heavy oil and brought to the North Slope by BP. West said the CHOPS well is drilled vertically. When production begins the progressive cavity pump will draw oil out of the formation and create small fissures that extend into the formation, allowing more fluids to flow.

The CHOPS wells are intended to allow the sand to flow in an up the well with the oil. A special production process plant has been built for the heavy oil test that will separate the sand, which is then trucked to a special facility in the Prudhoe Bay field where it is ground up and injected back underground in an injection well.

BP will test two CHOPS wells and one additional horizontal production well in the test program, West said.

The S-41 well was taken temporarily out of production to allow BP to replace casing where wear had occurred from a rotating rod that runs the progressive cavity pump, and to make changes in the processing plant at the surface to solve a gas-handling problem, but such startup problems were expected with a new production system, West said.

BP and other North Slope producers are looking to production from large unconventional oil resources like the Ugnu heavy oil to supplement declining production from conventional oil fields on the slope. The Ugnu oil produced at S-41 has an API gravity of 12, West said, but the oil quality from different parts of the formation is expected to vary. API gravity is an American Petroleum Institute measurement that is commonly used as an indicator of oil quality.

The test production wells were drilled to a deep part of the Ugnu that is about a 4,000 foot depth, but parts of the reservoir to the west are at shallower depths that will be more difficult to produce, and which may require a heat source to warm the oil if it is to be produced at all, West said.

BP and ConocoPhillips are also producing viscous oil, a somewhat better quality oil that is about 18 degrees API, from the Shrader Bluff deposit in the Milne Point field and the West Sak formation in the Kuparuk River field, which is nearby.

West said the Ugnu formation appears to have good porosity and permeability in the reservoir rocks, which are the pore spaces that hold the oil and gas fluids and the connections between the pores that allow the fluids to flow to a producing well. The porosity and permeability may be superior to that in some of the viscous oil formations on the Slope, in fact.

Tim Bradner can be reached at tim.bradner@alaskajournal.com.

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Republished with the permission of the Alaska Journal of Commerce