Dave Riley has more than 14 years of experience in the mining and oil sands industries, specializing in process and project management in both office and field settings.

His experience ranges from program management to front-end project scope definition to active field supervision of workers. Mr. Riley has a strong background in oil sands tailings and has managed a significant number of tailings capital projects, as well as a tailings process engineering department and operations field crew. Mr. Riley’s project experience has been as both an owner’s representative and an engineering consultant. He has participated in all aspects of projects from initial conception to detailed engineering through commissioning and startup.

What are Oil Sands?

Oil sands are a mixture of sand, water, clay, and a semi-solid form of petroleum called bitumen. After it is extracted from raw ore, bitumen is a very thick, black, and viscous substance that goes through intensive upgrading before it transforms into synthetic crude oil. Much like traditional mine ore bodies, the quality of the ore—the proportion of bitumen in oil sands—varies across deposits. The typical breakdown is 83 percent sand, 10 to 12 percent bitumen, four percent water, and three percent clay.

The Canadian oil sands exist in three distinct areas of northern Alberta, covering about 140,000 square kilometers (54,000 square miles). They represent the third largest proven oil reserve in the world, at 176 billion barrels. That is second only to Saudi Arabia and Venezuela.

How do you extract the bitumen for processing?

There are two processes that are used to recover oil sands bitumen—open pit mining and in-situ recovery.

Twenty percent of oil sands reserves are accessible using well-proven open pit mining processes. Oil sands ore is mined and transported to a crushing facility and then on to the extraction plant. During the process, hot water is added to the crushed ore, which creates a slurry of sand, clay, bitumen, and water. As the slurry settles, bitumen froth rises to the surface and is skimmed and treated to reduce waste going to the upgrader. Sediments such as rocks, clay, and sand settle to the bottom. The middle layer is removed for further bitumen recovery.

After the bitumen is sent to the upgrader, tailings—a mixture of clays, water, sand, traces of bitumen, and process chemicals—are pumped out to settling ponds, also known as tailings ponds. A significant portion of water released to tailing ponds can be recycled, but first needs to undergo further treatment before being released into the environment.

About 80 percent of oil sands reserves are buried too deep to be accessed by open pit mining. Bitumen located at depths great than 130 meters is recovered using various technologies categorized as in-situ (in-place). While numerous in-situ recovery technologies are being employed, the most common technique is called steam-assisted gravity drainage (SAGD). The SAGD technique can recover up to 55 to 60 percent of bitumen in the reserve.

In the SAGD technique, two wells are drilled in the formation, one slightly higher than the other. The upper well, referred to as the injection well, works as a kind of steam chamber and is used to inject steam continually into the ground. As the temperature rises in the oil sand formation, bitumen becomes more viscous and, through gravity, flows to the lower well, referred to as the production well. Finally, the condensed water and crude oil or bitumen is recovered to the surface by pumps and transported to an upgrader facility where it is transformed into synthetic crude oil.

The bitumen is heated to a high temperature or reacted with hydrogen under pressure to break the heavy molecules into lighter molecules, making it less viscous. Secondary upgrading further purifies the bitumen so it can be used as feedstock for oil refineries. In addition to the bitumen, coke, kerosene oil, naphtha, and other byproducts are obtained in the upgrading process.

How are tailings treated?

One of the biggest challenges facing the oil sands industry is how to reclaim the fine particles of clay in the tailings water. These components may never settle into a solid deposit. To help address this challenge, we are participating in long-term planning and numerous tailings projects for oil sands clients. Tetra Tech was instrumental in the design and implementation of pioneering tailings treatment processes that speed the reclamation process and increase the amount of water available for reuse.

We use a process called Atmospheric Fines Drying (AFD), which combines the addition of a polymer with evaporation to dry the Mature Fines Tailings (MFT). In the AFD process, the MFT is dosed with a polymer solution to coalesce the particles, which forms a slurry. This slurry is then deposited in lifts, or layers, over large areas of land known as a cell, which is an area of land that is slightly graded and has containment. Once the lift dries—typically through a freeze/thaw season—you can add successive lifts. These lifts effectively remove the MFT from the ponds and deposit them on the surface where it dries and the resulting fines can then be reclaimed.

Consolidated Tailings (CT) uses the addition of a coagulant to modify the surface chemistry of the MFT. Large volumes of a coagulant such as Gypsum or Alum are mixed into a slurry. MFT is pumped from the pond and the coagulant slurry is dosed into MFT along with reclaimed silica sand. The mixture is then re-deposited into the ponds, where it properly settles as a non-segregating slurry.

What are the challenges faced in the future development of the oil sands?

Some of the major factors and variables that affect the development of the resource include market developments and pipelines, crude prices, rising capital and labor costs, managing environmental impacts, global energy demands, technology innovations, and the global investment climate.

The largest impact currently is the coupling of two of these variables, namely pipelines and crude prices. A lack of pipeline capacity across North America has effectively stranded oil sands-sourced synthetic crude oil in northern Alberta. The major pipeline routes provide access primarily to the U.S. Midwest. Access to an almost singular regional market for a global commodity has put downward pressure on the prices of synthetic crude oil. Further approval and development of pipelines, allowing access to the U.S. gulf coast and Asian refining markets, are vital.