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Polymer Floods New EOR Addition At Pelican Lake

[Daily News] Canadian Natural Resource Limited plans to spend $40 million this year on its first commercial-scale polymer flood at its Pelican Lake heavy oil field in north-central Alberta.
Although it is still waiting for a conclusive response to polymer injection, based on what it has seen so far from its three-injector pilot, Canadian Natural is planning to move ahead with a full scale flood, David Payne, vice-president of Exploitation, West, told a recent enhanced oil recovery conference sponsored by the Canadian Institute.

Polymers are thickening agents that increase the mobility of the injectant fluid, increasing the sweep efficiency of a waterflood and reducing viscous fingering, the uneven distribution of the injectant into the formation.

"It looks like we are getting a really good response" as oil production is 200 barrels a day and increasing without any increase in water cut, he said.

Because polymer floods can increase sweep efficiency, Canadian Natural believes they will be most advantageous in heavy, heterogeneous reservoirs with poor sweep efficiencies.

The company has seen a delay in breakthrough from polymer injection which is exactly what it wants because in such cases, "the later you get a response the bigger the response will be because it means you are contacting more of the field," said Payne.

Canadian Natural is currently installing its second polymer mixing skid with plans for 14 pads in three distinct areas, he said. In 2007, Canadian Natural will be drilling downspaced wells and putting on production in the flood areas.

Plans calls for 124 wells a year to be drilled between now and 2010 with total expenditures of $890 million.

The three-injector pilot, which began in May 2005, cost about $1.7 million including about $1 million for the mixing and injection skid, piping and pads, $600,000 and $125,000 for the conversion of two injection wells. The cost of polymer works out to about 22 cents per bbl injected.

The polymer flood injection rate is maintained at 150 cubic metres per day but the injection pressure is increasing because of the increased viscosity of the polymer, said Payne. Canadian Natural expects that to level off below the frac pressure of the reservoir. "If it goes much higher than that, we will have to curtail our injection rate which wouldn't be a good thing because that will slow down the whole process."

The polymer pilot followed an earlier waterflood pilot (now commercial) at Pelican Lake which reversed declining production in the field. "Part of the nice thing about waterflood success is that it actually compounds itself," said Payne. "Now we can economically go where we couldn't go on just primary production in terms of other parts of the pool that aren't as good rock or as good oil," he said. "There's a nice double whammy out of the whole thing."

As part of the waterflood pilot, Canadian Natural decided to convert some wells to injection and drill some new producers and control its water injection. It achieved an increase in oil production to about 1,000 bbls a day (currently 1,500 and rising) from 500 bbls per day. At the same, the water cut was about 70%, a lot lower than in the first phase. The lesson was that for some reason limiting the injection rate controlled the viscous fingering, said Payne.

The company then decided to convert its producers to injectors for a while until it had essentially reached its fill-up time for what it had taken out on primary production. Output rose to more than 3,500 bbls a day from 200 bbls a day with a 10% water cut and elimination of the viscous fingering.

"The only issue there is you have to wait for your oil production; you don't get any incremental production until you build up the reservoir."

Canadian Natural is looking to enhanced oil recovery to increase the recovery factor of the 3.3 billion bbls of oil in place on its land which comprises 75% of the Pelican Lake field. While the resource is medium to heavy oil, extremely low operating and onstream costs translate into netbacks similar to those of light oil. Operating costs were $4.60 per bbl in 2005 and $4.44 a bbl in 2006.

At a five per cent recovery rate factor, primary production would amount to 165 million bbls of which about 85 million bbls have already been produced. It is growing its production rate and currently adding to development acreage and increasing its resource base through EOR.

It estimates that about 1.7 billion bbls are floodable which at a 15% recovery factor would yield a recovery of 247 million bbls of incremental oil for a total of 412 million bbls. About 130 million incremental bbls would come from the polymer flood.
"There is lots of oil left in place," said Payne. "If we can access that oil, there would be great upside."

In developing its EOR projects, Canadian Natural chooses to run pilots for two reasons, its inability to predict outcomes and operational challenges, the conference heard.

Without work in the field the company can't predict recovery rates, especially when it comes to sweep efficiency, said Payne. "Labs are very good at predicting displacement but if you assume a 100% sweep that will over-predict the recovery factor," he said.

In the case of a polymer flood, "core floods can't tell us how our sweep efficiency will be affected," said Payne. He also distrusts reservoir simulations, suggesting that was what had happened in the 1980s with CO2 flooding in West Texas. Operators believed the simulation forecasts and recovery factors and "they just didn't materialize."

A second reason to run pilots is because of operational problems, according to Payne. Water-polymer compatibility is a big issue and water salinity strongly affects the increased viscosity that polymers provide. "You really need to find a fresh water source," he said while acknowledging that is a major challenge because of concerns about water usage in Alberta.

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