Drillers tap hot spots

Special Report*

Bertram Drilling Corp is an exploration company out of Carbon, AB that incorporates different types of drilling in its business strategy. Its role is to identify major oil deposits, then recover samples which can be used to measure the potential of the formation.

The company runs a fleet of 36 helicopter-portable drill units and several other types of drilling equipment including track, wheel and buggy mounted rigs. These smaller portable rigs can get places larger rigs can’t, conducting seismic work. To do core work in the oil sands, Bertram uses Atlas Copco TH60 drill rigs. In total, the company has 17 rigs working in Canada and the United States.

The bulk of the coring work is done in a 90 to 120-day window of time, beginning at the end of December. For the most part, drilling in northern Alberta and Saskatchewan is winter work because much of the region is spotted with muskeg and swampy ground that can only be traversed when frozen. Although Bertram’s crews usually work at -35 C– at that point steel becomes brittle — temperatures did reach -56 C last winter and the cold is hard on equipment.

Oil Security

Alberta’s oil reserves are estimated at 280-300 billion barrels (Gb), but those numbers will become more than estimates through the work conducted by Bertram and others. As a comparison, Saudi Arabia’s oil reserves are listed at 240 Gb. Total reserves for Alberta, including oil not recoverable using current technology, are estimated at 1,700-2,500 Gb.

The oil sand formation is just that, heavy oil deposited in a layer of sand. The paleotopography is dated to the lower cretaceous period. Below the oil sands are hilly limestone deposits and the depth of the oil follows the contour of the land with thin and thick deposits.

According to Brian Bertram, “The sands are massive and only 10% have been quantified.” The depths of the oil sands vary and are well within the pullback range of the TH60 rigs.

Drilling 1600 m apart in a grid pattern, the formation is mapped out. Cores are then taken closer and closer down to 100 m until a clear picture is identifiable. Working just east of the Alberta border in Saskatchewan, northeast of Fort McMurray, the forested landscape allows coring work during the summer.

Currently, a number of drilling companies are working in the region doing both exploration and SAGD drilling. (See adjacent box on page 23)

Retrieving the Core

Once identified, the oil can be recovered through one of two methods. Where it is shallow near Fort McMurray it is being scraped up with loaders. The deeper formation, like that at Axe Lake, will be recovered through SAGD operations.

Drilling starts like a traditional mud drilled borehole. Bertram’s drill supervisor, Wes McMann, at the Axe Lake Project says, “Drilling the surface hole is done with bentonite mud whereas the core hole requires a more slippery mud.”

A surface hole is drilled with a 25 cm tricone bit to a point above the formation where the spotting of oil begins appearing in the cuttings. This is called the core point. The hole is then cased and cemented with 18 cm casing.

Once the surface hole is finished, the coring begins. Going back in the hole with a 16cm, 16-cutter, core bit at the end of 11 cm core pipe, the bit is advanced through the formation. As the bit advances, drilling stops in increments from as little as 10 cm to 300 cm to retrieve the 6 cm core sample.

“A quality recovery is when 95% of what was drilled comes out of the hole,” says McMann.

When the bit is advancing, the core sample moves up and into the core pipe and then into a 3 m section of pipe, called a retrieval barrel. Inside the retrieval barrel is a 6 cm PVC pipe that firmly holds the sample in place. At the bottom of the retrieval barrel is a pronged metal piece, called a basket, which allows the sample to move into the barrel. The basket secures the sample so it doesn’t fall back into the hole. Once the driller stops advancing the bit, a cable lowers a retrieval pipe into the hole. At the end of this section are fingers that lock into a landing ring on the top of the retrieval barrel. The retrieval barrel is pulled from the hole.

The sample length will be checked for length and geological properties and the process is repeated. Once through the oil sand strata, and at least 3 m into the limestone, the hole is complete.

“Our job is to define the oil formation,” said McMann. “The hole is done when we reach the bottom.”

*Information for this Special Report provided by Atlas Copco.

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Steam assisted gravity drainage enhanced oil recovery

Over 90% of the world’s heavy oil and oil sands are deposited in Canada and Venezuela. Up to 90% of Canada’s estimated reserves could be recovered by steam assisted gravity drainage (SAGD) operations and 10% by surface mining. In this process, two horizontal wells separated by a vertical distance are placed near the bottom of the formation. The top horizontal well is used to inject steam which rises, forming a large steam chamber above the well, and the bottom well is used to collect the produced liquids (formation water and oil). The rising steam condenses on the boundary of the chamber, heating and drawing out the oil to the production well. The process leads to a high recovery and high oil rate at economic oil-to-steam ratios (OSR).

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