In-Situ Bitumen Extraction
Only 20% of Alberta's bitumen reserves are close enough to the surface to be mined. The remainder can only be feasibly extracted in-situ (or in place) using steam. Although in-situ bitumen extraction traditionally had very low recovery rates, recent advancements in technology have allowed for significant process improvements. Smaller processing plants and higher production rates have greatly improved the profitability of in-situ extraction, which has become increasingly more popular in the oil sands and expects to lead the growth in bitumen production through the next few decades.
In-situ facilities consist of the following basic unit operations:
a series of well pads scattered throughout the oil sands deposit
a steam and power generation plant which provides power for the facility and high-pressure steam for injection into the wellheads
a central processing plant where the oil and water emulsion produced at the injection wells is separated
a water treatment plant where the recovered water is cleaned and recycled back into the process, and
a product storage facility where the bitumen is diluted with condensate for storage and transportation via pipeline.
An in-situ processing plant is generally much smaller and simpler than an oil sands mining facility. However, bitumen can only be extracted in-situ if the oil sands deposit is deep below the surface. Most in-situ deposits lie at least 200 meters below grade.
All commercial in-situ facilities contain four basic components:
bitumen production, and
In each case, steam is injected deep into the reservoir, allowing the bitumen to heat up and liquify. The bitumen emulsion is then pumped up to the surface, and sent to a separation plant, where the water (or condensed steam) is removed from the bitumen. Clean bitumen is then diluted and sold to market (either an upgrader or refinery, depending on the quality of the bitumen). The process water is cleaned, treated and recycled back to the steam plant.
IN-SITU VS MINING: PROS AND CONS
In-situ extraction of bitumen has become increasingly popular in recent years and expects to lead the growth in bitumen production over the coming decades. In-situ facilities can be a lot smaller and do not require the same economy of scale as oil sands mining operations, making them cheaper and faster to bring online.
THE IN-SITU ADVANTAGE
Smaller footprint: The surface area required for the wellheads is very small relative to the oil sands reserve deposit size. In-situ facilities therefore have a much smaller footprint than surface mining operations. In-situ requires about 1/7th the land area of an equivalent-sized mining facilities. Alberta's oil sand mining footprint is actually only 3% when measured by square footage.
More efficient water usage: In-situ operations use water for steam production, which is mostly recovered and recycled back into the process plant. Fresh water consumption rates are therefore much lower than mining operations which require large volumes of water to slurry the oil sands. In-situ facilities typically require 1/5th the fresh water volume of an equivalent-sized mining facility.
No tailings pond: Much of the sand contained in the oil sands deposit is left in the ground and never comes to surface. In-situ operations therefore do not require large tailings storage ponds and have no need for reclamation.
Lower cost: Since there is no mine or tailings pond, in-situ operations require much less capital, are quicker to build, easier to bring on-line and generally less expensive to operate. These facilities can be built in phases and do not require the same economy of scale as surface mining operations.
Lower bitumen recovery rates: Recovery rates for in-situ facilities can vary greatly, typically from 40 to 60%. Despite significant technological improvements in recent years, in-situ recovery rates are still much lower than mining operations which typically recover over 90% of the bitumen contained in the oil sands.
Lower certainty: There is a larger degree of uncertainty in terms of positioning of the wellheads and expected recovery rates. Once steam is injected, it can take several months before a drop of bitumen is produced. This makes the economics of in-situ operations somewhat more variable, particularly in newly developed areas.
More GHG emissions: In-situ extraction requires a large volume of steam to heat the bitumen in the ground. This steam is produced by burning natural gas. In-situ facilities therefore generate more greenhouse gas (GHG) emissions per barrel of bitumen produced as compared to an oil sands mining facility.
Not easy to stop and start: In the event of an unexpected disruption, it is difficult to just shut-off steam, particularly in new facilities. Once steam is cut off to the well head, the reservoir will begin to cool. A very mature well (one that has been steaming for several years) will retain its heat relatively well and be much slower to cool. However, a new facility might cool down very quickly and take a long time to restart once steam is re-established. In contrast, mining facilities can be safely shutdown in less than a day and restored back to nameplate capacity within only few days.
Advances in technology have greatly improved reliability and bitumen recovery rates for in-situ operations. In fact, in-situ bitumen production is expected to surpass production from surface mining in the next few years. There are 2 common thermal in-situ techniques employed in the oil sands:
1. Cyclic Steam Stimulation (CSS)
2. Steam-Assisted Gravity Drainage (SAGD)
Both CSS and SAGD have identical central processing facilities. The difference lies in the positioning and number of wellheads.
1. CYCLIC STEAM STIMULATION (CSS)
A single well is drilled into the oil sands deposit.
High pressure steam is injected into the reservoir to heat the bitumen and reduce its viscosity. This steam continues to be injected for several weeks in order to fully saturate the reservoir.
The bitumen is then allowed to soak for several days or weeks in the hot pressurized reservoir.
As the reservoir cools, this provides the driving force to bring the oil up to the surface. The flow is then reversed so that the bitumen/water emulsion can be pumped back to the surface. This production phase can last for several weeks.
At the processing plant, the water is removed from the bitumen, treated and recycled back into the process. The bitumen is sent to an upgrader for further processing or diluted and sold directly to market.
Imperial Oil's Cold Lake facility was the first in Canada to commercialize CSS recovery of bitumen. Initial recovery rates were only 20-25%, but recent improvements in technology have boosted recovery rates into the 50% range for some operations.
2. STEAM-ASSISTED GRAVITY DRAINAGE (SAGD)
Two horizontal wells are drilled approximately 5 meters apart, one above the other. Well depth can vary anywhere from 150 to 450 meters. Each well can be up to 1,000 meters long.
High pressure steam is injected into the top well, or the injection well. The hot steam heats the surrounding bitumen.
As the bitumen warms up, it liquifies and begins to gravity flow to the lower well, or the producing well.
The bitumen and condensed steam emulsion contained in the lower well is pumped to the surface and sent to a processing plant, where the bitumen and water are separated.
The recovered water is treated and recycled back into the process. The bitumen is sent to an upgrader for further processing or diluted with condensate and sold to market.
SAGD is a continuous operation, allowing for much higher production rates than CSS and improved bitumen recovery, near 60% in most cases. This technological breakthrough has enabled a major increase in bitumen production from the oil sands with minimal land disturbance.
WATER DISTRIBUTION CIRCUIT
Thermal in-situ oil sands facilities use water and natural gas for the generation of steam. The quantity of water required is much lower than an equivalent mining facilities - only 3 barrels of water is needed to produce 1 barrel of oil. However, water quality is very critical when used for steam generation. Water treatment is therefore a very important component of any in-situ operation. A typical in-situ facility recycles about 90% of the water used on site. Most of the fresh water supply (make-up water) is sourced from groundwater aquifers.
BITUMEN EXTRACTION IN-SITU: WHERE THE GROWTH IS
Throughout the 1990s and into 2000, much of the growth in the oil sands was focused on mining. However the past 10 years have seen major expansion of in-situ bitumen extraction, particularly in the Athabasca Region near the town of Fort McMurray.
There are several dozen commercial in-situ operations and a handful of small demo plants scattered throughout central and northern Alberta. Facilities in the Cold Lake area commonly use CSS to extract bitumen while most other facilities use SAGD. With the exception of production from Firebag and MacKay River, most facilities produce a heavy diluted bitumen (or Dilbit) sold directly to market, without an intermediate upgrading step.