Q. What is thermal recovery of heavy oil?

A. The majority of sub-surface heavy oil will not flow towards a well bore in sufficient quantity to be economically viable. Thermal recovery involves heating up the reservoir, thereby lowering the heavy oil’s viscosity enabling it to flow to the well bore. Traditional thermal recovery methods using vertical wells such as cyclic steam stimulation (CSS) or “huff’n’puff” and steam flooding have recovery factors usually less than 25% of the original-oil-in-place (OOIP) without any in-fill drilled wells and other means of enhanced oil recovery.

 Q. What is SAGD thermal recovery?

A. The most significant development in thermal recovery has been the steam-assisted gravity drainage (SAGD) method, which was initially developed to recover the tar type heavy oil in the Canadian oil sands. This involves drilling two parallel horizontal wells, one above the other, along the reservoir itself. The top well is used to introduce hot steam into the oil sands. As the heavy oil thins and separates from the sand, gravity causes it to drain into the lower well from where it is pumped to the surface for processing. Even though the injection and production wells can be very close (between 5 and 7 m), the SAGD mechanism causes the steam-saturated zone (known as the steam chamber) to rise to the top of the reservoir and expand gradually sideways and eventually allow drainage from a very large area. SAGD significantly improves heavy oil recovery by a factor of between 50 and 60% of the original oil in place (OOIP), and is therefore more efficient than most other thermal recovery methods.

Q. If SAGD is so advantageous, why has it taken so long to become globally acceptable?

A. The key element of SAGD is that the two wells need to be parallel and horizontal. It is only in the last ten to fifteen years that directional drilling technology has been able to achieve these two characteristics with any degree of certainty.

Q. And what about “huff ‘n’ puff”?

A. Huff ‘n’ puff employs a pattern of vertical wells. Typically, pressurized steam is pumped down a well for weeks and sometimes months, thoroughly heating the reservoir near the well. The process is then halted, usually for several weeks, which allows the heavy oil to become separated from the reservoir sand, and then the heavy oil is artificially lifted from the same well. This technology has been successfully used for many years but is fast being replaced by the SAGD method and is now only considered in newly developed heavy oil regions where SAGD is not suitable.

 Q. What is thermal modeling?

A. Numerical modeling is a useful tool, which allows engineers to predict the oil recovery performance by solving a set of flow equations governing the recovery process mechanisms. For non-thermal oil recovery—we have “black oil models” and “compositional models”.  For thermal oil recovery, we have “thermal models” not only solving the flow equations but in addition, the energy equations that take into account the heat transfer between the reservoir fluids and the rock. A great deal of work is currently underway on advanced thermal modeling for more complicated steam-assisted recovery processes, as well as in-situ combustion processes.

 Q. What are the benefits of thermal modeling?

A. Thermal modeling is designed to take out the guesswork from thermal recovery methods. For example, if injecting steam into a heavy oil reservoir or undertaking in-situ combustion, you need to be able to predict what will happen to allow you to design your field operation.

 Q. What is thermally enhanced chemical recovery?

A. I do not know any thermally enhanced chemical recovery methods being used in the field nowadays. If the chemicals are solvents such as light hydrocarbons, for example, propane or butane, there are a number of heavy oil recovery methods, such as thermal solvent methods and the solvent-based SAGD hybrid methods, being developed and field tested in Canada. The thermal models then need to be modified to handle this type of phased behavior between the hydrocarbon additives in the steam and the heavy oil itself. This is one of the directions in which thermal modeling is progressing.

 Q. A more dramatic form of thermal recovery is fireflood…what exactly is it?

A. Fireflood is when you inject compressed air down the injection wells, normally with some thermal energy to form a burn-front in the reservoir. The heat and the products from this combustion between the oxygen and oil, drives the remaining heavy oil towards the production wells.

 Q. Can you do modeling for fireflood?

A. Most thermal modeling tools can handle fireflood; you just need to incorporate the chemical reactions of the combustion into the model. But there are not that many fireflood projects in the world and, therefore, very little field data is available to verify fireflood predictions.

 Q. What are the environmental impacts of thermal recovery?

A. The net energy advantages in using such methods are questionable. You are generating a lot of CO2 emissions when you are generating steam, which explains why engineers are looking at efficient surface steam generation, down-hole steam generation and in-situ combustion options. It doesn’t mean that you don’t have any CO2 emissions, but you are taking a responsible stance.

 Q.    This is quite a dramatic step forward.

A. Actually in-situ combustion and down-hole steam generation are both making significant inroads. However, I think environmental concerns are going to be an issue for heavy oil production in the future. Heavy oil is by-and-large a high-volume business where you have to drill more wells in a heavy oil field than you do in a conventional oil field. This brings with it certain issues such as environmental footprint and greenhouse gas emission.

 Q. Based on the environmental drawbacks, why is down-hole steam generation not being universally embraced? And why is the heavy oil industry still employing surface steam-generation technology?

A. Down-hole steam generation technology is still in the development stage. If it is deemed to be successful, then there is a very good chance the industry will be switching to these methods, especially for offshore heavy oil application. But bear in mind that even for the same thermal recovery method, recovery performance from down-hole steam generation can be quite different than that from surface steam injection.

 Q. Will the potential for offshore heavy oil production impact upon environmental advances?

A. Of course. When you are developing heavy oil offshore fields you do not have the space to accommodate steam generation equipment. For this reason, in-situ, (sub-surface) steam generation is an alternative heavy oil recovery method that is attractive to offshore installations.

 Q. And will nuclear power be used for steam generation?

A. This is a very sensitive issue at least here in Canada. Yes, the technology does exist, but the public has to be happy with it before the industry follows.

 Q. And what is the next big break through in the heavy oil industry?

A. I do not think it will be on the recovery side. It is hard to imagine another big break through such as SAGD that significantly improves the recovery factor of a thermal recovery method. I believe that it will be in down-hole equipment and down-hole monitoring. Down-hole equipment such as pumps and sensors needs to be improved to withstand the high temperature for the thermal recovery methods. Better down-hole monitoring will allow optimization of the recovery performance.