Canadian Mining Journal

Feature

Huge Expectations

The goal was an ambitious one: from a resource estimated at 174 billion barrels, Muskeg River Mine bit off 300,000 tonnes of processed oilsands each day, to deliver 155,000 barrels of bitumen, then drive that recovery as high as 525,000 barrels...



The goal was an ambitious one: from a resource estimated at 174 billion barrels, Muskeg River Mine bit off 300,000 tonnes of processed oilsands each day, to deliver 155,000 barrels of bitumen, then drive that recovery as high as 525,000 barrels a day. Better still, do it in such a way as to silence a highly vocal environmental movement, while maximizing operational efficiency and preparing the ground for even bigger things – like an expansion to create an additional 100,000 barrels a day.

By any standard, Shell’s promise at the site of Muskeg River Mine in 2002 was a big one, but given the resources brought to bear the company’s optimism seemed justifiable: a starter pit as deep as 90 m and 4 km2, two 14,600-tonnes/hour Krupp semi-mobile gyratory crushers and one of the largest conveyors in the world to transport the crushed ore to the silo. Add to these, innovations like the first caustic-free, dual flotation bitumen recovery process and a fleet of 400-ton haulage trucks and you’d be hard pressed to bet against them.

Think globally, and really act locally

With demand increasing and conventional crude oil resources dropping precipitously, the consensus is that heavy oil or bitumen represents the next best hope for the world’s oil industry. The two most important deposits of bitumen are the Athabasca Oil Sands in Alberta and the Orinoco extra heavy oil deposit inVenezuela. Both, of similar size, have two-thirds of total global oil deposits. Both also feature a bitumen-based oil extract that is very dense and extremely viscous and frequently likened to heavy molasses. These features make it harder to process than conventional crude oil extraction – and consequently more expensive.

That cost for Shell and other members of Athabasca Oil Sands Project in 1999 was offset initially by the relative ease of the mining. The bitumen deposit north of Fort McMurray is fairly close to the surface and the depositional environment, eliminating the need for blasting and making the removal of overburden relatively straightforward. Since the Muskeg River Mine opened in 2002, the mining has been made even easier by Shell’s investment in a conventional truck and shovel operation that has grown as the mine’s success has grown – today standing at nearly a dozen Cat 797B haulers and six Bucyrus 495 HF electric rope shovels. Their most spectacular acquisition, however: Caterpillar’s first 797B, 400-ton haul truck, which has mushroomed from one unit to over 56 of the B and newer F series 400 ton haul trucks.

In the absence of explosives, says Manager of Technical Assurance-Technology David Corriveau, Shell decided on a fleet of D10 and D11 tractors equipped with rippers. One issue: severe cold. “Because we do get down into the -40 range and colder with wind chill the ore will freeze at four feet deep. So we break it up. We just fragment it down so it’s not one large chunk.” At the same time, Corriveau says crews minimized ripping by, among other things, maintaining a consistent digging plan within an active face.

“Don’t work one face and then move away, letting that first face freeze up and then move back. That way all you really had to rip was the first time you’re into that face in a given shift. And often that’s done as part of the early fragmentation of the dirt, before you feed into the shovel.”

Some changes are unavoidable over time. Take the ore deposit itself. Originally the depth of the pit allowed recovery from the full thickness of the deposit, consisting of a high grade coarse fluvial ore and high and lower grades of non-coarse estuarine ore and tidal. “We’re still in that same ore body within the Muskeg River Mine,” says Corriveau. “The way we had staged it is we were aggressively extracting the coarse fluvial; now we’re much more into the estuarine faces, which is still a high quality ore.”

Mercifully what has not changed, says Corriveau, is location of mining operations relative to the 45-meter-tall crushed ore silo situated about 1 km northwest of the plant. Shell fully expected that mining would move farther northeast, away from the silo once Cell One of the pit reached about 4.5 km(2) after four or five years. It was for this reason that the crusher area was built of mechanically stabilized earth, a technique that is economical to build and facilitates movement of the crushers. So far, that move hasn’t happened, says Corriveau, from Cell One or Cell Two.

“We’re now migrating up into Cell 3 north and east of the original cell. But we haven’t had to move the silo or the crusher locations yet. We’re still within an economic haul distance to reach the ore pocket.”

The centre piece of that ore pocket is Muskeg River’s conveyor – with a 2,500-mm-wide belt and enough horse power (10,400) to move 18,000 tonnes of oil sands per hour. Goodyear still ranks the conveyor as the largest or among the largest conveyor systems in the world. At one point, says Corriveau, Shell proved the conveyor’s real mettle by taking its output to a peak capacity of more than 26,000 tonnes an hour. Corriveau is quick to add, however, that 18,000 tonnes per hour is more than sufficient to meet Shell’s output demands.

Which is not to say that there haven’t been challenges along the way. The biggest occurred in February 2006 when a piece of liner fell from a truck box ripping into the conveyor belt. Corriveau says the mine reacted to the tear quickly, putting an undamaged portion of the belt to work, but suddenly the mine and Scotford Upgrader had been transformed to a single-train operation producing at approximately one third of design rate. This was followed in March by a full two week shutdown to install a spare conveyor belt on site.

But the real problem, says Corriveau, was not the liner from the truck box puncturing the conveyor belt. It was the absence of an effective inspection plan for truck box liners for all trucks in service at the time.

“So we changed procedures both for inspection and which trucks are allowed to dump into the hopper. We now restrict it to our own inspected 797s fleet and we’ve never had to replace a belt for that reason since.”

Strong, sustainable expansion

Of all the innovations at the Athabasca Oil Sands Project none is as significant as the one introduced to the extraction plant adjacent to the Muskeg Mine. Typically, bitumen is diluted with solvent naphtha, and chemicals and heat applied using a coker unit to produce synthetic crude oil. To produce a cleaner bitumen product, Shell’s process designers “went down a different path” says Corriveau, settling on Paraffinic Solvent Froth Treatment, a relatively new method of bitumen froth treatment that produces lower levels of contaminates and requires less energy. In essence, says Corriveau, instead of stripping out carbon to make coke, Shell would add hydrogen. The result says Corriveau: “for every barrel of bitumen we send down we get 103 barrels of saleable product to the refinery.”

The absence of caustic and other reagents to recover the bitumen is an environmental plus. Shell’s primary focus for minimizing its foot print, however, remains upstream.

“Instead of opening up the whole shebang at once we open it up using these cells, pushing back and salvaging all of the mineral soils first. We then limit the expanse of our tailings facility to just one external tailing facility and then move progressively into the pits so that we can contain our tailing in-pit as well.”

In 2006, aided in part by twinned extraction circuits, Shell came within spitting distance of its interim recovery goal of 219,000 bbl/day. It has, however, reached – and exceeded – another target: processing 300,000 or more tonnes of ore feed per day. Even better, it’s squeezing more bitumen out of each tonne of sand, i.e. 155,000 barrels out of 260,000 tonnes of ore feed.

In 2006, Shell also received approval for an expansion of Muskeg River Mine and nearby Jackpine Mine,
an expansion intended to develop Lease 13 which contains more than five billion barrels of mineable bitumen – or about twice the conventional oil reserves remaining in Alberta. Approval of the expansion by federal and provincial regulators has led to furious construction activity, says Corriveau – development of an entire new mining pit, crushing, conveying, extraction and tailing facilities and a 2,500 bed village to house construction crews.

Corriveau points out that Shell has kept its word about developing an environmentally sustainable mining and processing operation. The company has done that, he adds, while making sure he has the resources he needs to ensure the operation is productive.

“Shell has been living up to its environmental commitments and not underfunding the business. Shell lets me get on with things that I might not have been able to do at other mining companies. I’m proud of that part of it,” said Corriveau.