Canadian oil sands are located in the Western Sedimentary basin of Alberta and Saskatchewan. The total proven reserves of 180 billion barrels places Canada third in size of proven reserves behind Venezuela and Saudi Arabia. The geographical spread in size is as large as the United Kingdom.
Oil sands are a naturally occurring mixture of sand, minerals, water and bitumen. This is extracted from sands and is three to four times thicker than conventional crude. It needs diluting and heating to flow. Bitumen is a thick form of crude oil, which at room temperature does not flow as its API gravity is 10 or below, hence it is heated with lighter hydrocarbons to flow and it needs to be upgraded before it can be used by refineries to produce fuel. The process of separating oil from Oil Sands involved two steps:
- Bitumen is extracted and then sold in the market.
- Bitumen is upgraded to produce synthetic crude oil which is sold in the market.
This synthetic crude oil is then refined to produce gasoline, diesel and other products (similar to conventional oil refining).
How oil sands are produced in Canadian Arctic weather
Oil sands oil is viscous so it does not come gushing out as in conventional production. The recovery methods are:
- Pit or surface mining, conventional surface mining to produce oil: Approximately 20% of recoverable Canadian oil sands reserves can be extracted using surface mining for deposits less than 250ft (75meters) from the surface. In mining the producer removes trees and vegetation to clear the area and then large earth moving equipment removes clay, earth and any material that lie over the bitumen. The exposed layers of bitumen are excavated using shovels and carried into large trucks to crushers that break big lumps into small particles. Hot water is mixed with this to form slurry which can be transported via pipelines into separation equipment followed by extraction plants where this slurry is flowed into separation vessels and bitumen is separated from sand slurry (in three layers:fine sand, middle – clay and water, top – water including some bitumen)
- This water including bitumen is called froth and this is further skimmed off and spun in centrifuges and inclined plate separator units to remove the remaining sand and water from the bitumen while the leftover sand, clay and water is recycled back into the extraction plant for re-use.
- The froth contains 65% bitumen and 35% water including fi ne solids. The froth is further processed by solvent and diluents (such as naptha) to make it suitable for marketing and/or further processing.
Oil sands plant. Photo courtesy of Suncor Energy Inc.
About 80% of recoverable oil sands deposits are too deep for surface mining hence these are recovered using drilling techniques in heavy oil production such as: In Situ: The drilling is conducted and two pipes are inserted in kilometers of lengths 5m apart. Steam is injected from the surface to heat the reservoir of bitumen to allow it to flow to the ground. One pipe is used as an injector (steam injection) and the second is used for recovery of the oil (like a straw sucking the drink from a glass full of ice and drink).
The steam injection is achieved through cyclic (huff-and puff) or steam stimulation(CSS) and continuous steam injection is known as steam assisted gravity draining(SAGD)
The CSS method: This is a three-stage process that is based upon drilling a single vertical well to an oil sands formation. In the beginning, high temperature steam is injected into the formation through the well to heat the bitumen, i.e. a soak cycle. After weeks of soaking, the mixture is pumped above the ground through the same injector well. After recovering the bitumen, typically over six months, steam is injected again into the well and the cycle repeats until the bitumen recovery stops. This method gives 35% recovery.
The SAGD method: This is built on the success of horizontal drilling technology and the process uses a pair of parallel horizontal wells, the upper well creating a high-temperature steam chamber. The steam lowers the viscosity of the thick bitumen which is then pumped to the surface via the lower well called the production well. The heated bitumen is pumped to the surface via the production well. In this process the steam is continuously introduced through the well. This method gives 65% recovery.
After its production, bitumen is either processed in the refineries directly or converted into upgrading facilities before it is processed in refineries.
The downside of in-situ development is that it often requires lots of energy, most of which comes from burning natural gas to heat water to make steam generating unwanted greenhouse gas emissions. Extra care is required in the selection criteria for valves used in SAGD to mitigate, reduce and meet the requirements on fugitive emissions.
Valve engineering and advances in metallurgy
Canadian oil sands produce oil in a harshen vironment and tough situations.
Metal seated valves are used in all of the services associated with SAGD and CSS and the valve industry has developed various valves, including pressure seal gate valves, for steam production and injection. This has led to the evolution of exotic materials.
Some of the metal seat hard facing and coating technology includes cobalt-based overlay materials for abrasion resistance and tungsten carbide for improving seating surface hardness. Recently, proprietary ultra-hard tungsten carbide version shave found a place in the industry as has nitriding (a heat treating process that diffuses nitrogen into the surface of a metal to create a case hardened surface), and molten salt bath ferritic nitro carburizing(a range of case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures).
Depending on a variety of factors, boron carbide and ceramic coating have also proven successful.
Photos courtesy of Suncor Energy Inc.