A new mining method under development holds the potential to liberate billions of barrels of oil from the previously difficult to mine “middle zone” of Alberta’s oil sands.

Known as gravity-assisted bitumen extraction (GABE), the technique is designed to recover bitumen from oil sands deposits in the region between 50 metres and 250 metres underground. “[The middle zone] is the area that’s too deep to mine [by conventional methods] and too shallow for thermal operations,” explained Scott Morton, founder and CEO of Alberta-based Drift Resource Technologies, which developed and patented the process.

Open-pit mining is the preferred technique for oil sands extraction down to about 50 metres, he said, and below 250 metres, technologies such as steam-assisted gravity drainage (SAGD) are used to liberate the bitumen. However, that middle zone has been problematic to extract. Drift estimates that the middle zone contains approximately 102 billion barrels of oil.

“Lots of different types of technologies have been tried,” he noted. “There’s all kinds of examples of people trying to attack this middle piece, and no one had been able to do it.”

GABE, he said, uses existing commercial technologies in novel ways to solve the problem. “What we’ve created is not so much of an invention, it’s more of an innovation,” he observed.

Morton, a hydrogeologist who has worked in the oil and gas industry for 25 years, began digging into the issue in 2021; he founded Drift and spent almost two years doing research and developing the patent with a team of engineers, geologists and operations personnel. GABE is now ready for a pilot test, which the company hopes to perform this year.

How it works

The GABE technique integrates three established commercial processes to address the challenges of the middle zone’s oil sands deposits.

The first process involves drilling vertical wells to determine the appropriate depth for the bitumen deposit, and then directionally drilling and casing a shallow horizontal well. At the end of the horizontal well, the last 10 metres of the casing is specially designed as a half-moon-shaped casing that allows access to the deposit and acts as a tray for the auger. The auger is sent down the well with an under-reamer attached, where it expands the hole, destabilizing the sand, which falls onto the auger to be pulled up to the surface. Up to that point, Morton acknowledged, the process bears a resemblance to the block caving done at some copper and gold mines, which also relies on gravity to recover the ore.

Once the material is at the surface, the second process is to wash it in a once-through hot water process based on Karl Clark’s hot water separation process to retrieve the bitumen, resulting in a froth consisting of approximately 55 per cent bitumen, 40 per cent water and five per cent solids.

But, Morton noted, once that bitumen is recovered, the residual material—a mix of sand, water and some unrecoverable bitumen—is usually sent to a tailings pond. “We wanted to come up with a better way, and to reduce the land use,” he said. “With that in mind, we looked at the process on the surface, and we said, ‘what can we do? What technology can we borrow from?’”

That technology they identified, which is the third process used in the GABE method, is paste backfill.

“I didn’t know anything about paste backfill, except that it existed,” Morton said. He asked some engineers he was working with at Golder (now part of WSP) where he could find some expertise, and was introduced to Sue Longo, principal engineer at WSP, who has particular expertise in paste backfill and surface disposal work.

Longo is working on the paste backfill recipe for GABE, and engineering the paste backfill production and distribution system. She has also answered questions about the technology posed by Morton’s team, as well as by the Alberta Energy Regulator and other stakeholders.

These included providing advice on paste backfill behaviour and its engineering properties—such as flowability, permeability and strength—as well as costing information for project development purposes, Longo explained. She also provided what she called “general dos and don’ts when it comes to using paste for mine backfill.”

Morton said Longo has been a great help and an integral part of the GABE development team. “Her paste backfill knowledge allowed us to complete the process with an understanding that we just didn’t have [before],” he said.

The paste backfill—which is composed of what is left of the waste material after usable aggregate has been screened out for future sale, plus water recycled from the extraction process and binders from the cement industry—is then infused with carbon dioxide (CO2) from offsite carbon capture projects to create calcium carbonate, which sequesters the CO2.

That mixture is pumped into the vertical wells previously used for investigation, where it flows to fill the void left by the oil sands recovery. The vertical wells are spaced at 100 metre intervals, and they serve three purposes: along with backfill deployment, they are also used for geological investigation and production monitoring. During production, the vertical holes allow for observation via cameras that are lowered into the underground voids to monitor the paste backfill deployment and general stability of the voids.

“The biggest challenge for me on the project was trying to find the right recipe balance [for the paste backfill] between flowability and strength,” Longo noted. “We want the paste backfill to flow to fill the void, but not to flow too far and create issues with the oil sand extraction part of the [GABE] system. This piece has to be balanced against the strength requirement to support the back [or roof] to avoid failures that could not only compromise the mining, but also create disturbances on surface such as subsidence, sinkholes or cracking.”

As extraction and backfilling proceed, the horizontal well casing and auger are pulled back to access more of the oil sands deposit.

“It’s a very practical solution to a long-standing problem,” Morton said. “We knew the resource was there [and] that it was valuable. I came up with the idea, but I knew I wasn’t going to be able to do this alone, so I reached out to my network to find the technical experts we needed. This is a multi-disciplinary solution—we’ve leveraged professionals from oil and gas and mining.”

Engineering optimization

Morton noted that, since GABE has been set up as three different processes, it is flexible and adaptable. All three are proven technologies that work independently, and the purpose of the planned pilot test is to demonstrate that they can work together in this application in the field.

“If a new technology for surface extraction of bitumen comes along, well, we’re very flexible to pull that in. You could just swap [the old technology] out if you wanted to,” he observed. “And same with the paste backfill. It’s an engineered product, and if we come up with a better recipe, or a better binder, or something like that, it’s easy to adapt those recipes. We feel really confident that this [could] work in any environment for oil sands.”

Longo added that since this is an innovative step change in terms of mining methods, there are naturally still questions to be answered. “We know that we will learn things and some of our assumptions will need to be adjusted once we get in the field and try out the method,” she said.

Morton pointed out that the process is also more energy-efficient than other methods. “There’s no heat and no pressure in our [mining] process,” he said. “It’s all mechanical and gravity driven.”

Unlike SAGD, which needs to heat the reservoir before extracting any oil—a process that can take six to 18 months—GABE begins producing bitumen immediately after drilling is complete.

It also recycles the water from its surface activities to create the paste backfill.

“What we try to do at Drift is to marry the economic and environmental benefits,” Morton said. “They’re important to us, so we want to make sure that we’re doing both. We want to create value for the shareholders, and we also want to make sure that we respect the land that we work on.”

Drift is currently raising capital for its pilot test that will take place over 10 days at a non-commercial location, and which Morton said will cost an estimated $5 million. The company has all of the regulatory approvals in place, so, assuming that it secures funding, he hopes to run the pilot in the fourth quarter of this year.

“We want to test all of the systems. But the main part of the pilot is to make sure that the models and the math are checked,” he said. “Then we can build economics. We have pro formas, but we want hard data before we make final decisions.”