Interview - Dr Ali Suat Bagci

Bio of Dr. Bagci

Q. Why are heavy oils suddenly important?

 A. There are three reasons why heavy oils have suddenly become important. Firstly, the sheer size of the reserves available for exploitation, estimated at over 6 trillion bbls. This is almost 6 times the world’s entire currently known conventional oil reserves. Secondly, conventional light crude oil deposits are being depleted quicker than they can be either discovered or brought on stream, and these deposits are not finite. Thirdly, the oil price continues to rise and, as a result, both national and independent oil companies are looking at these heavy oil deposits with interest.

 Q. Why have these heavy oil fields not been produced before?

 A. Heavy oils are not only difficult to produce but also require different oil recovery techniques. In order to produce these fields in sufficient quantity we need to resort to a number of enhanced oil recovery methods, which usually involve some form of thermal oil recovery techniques.

 Q. Is the injection of hot water still employed as a thermal oil recovery method?

 A. This method was the forerunner of all modern thermal enhancement methods and although it has been used since the 1940s, it is still seen by many as the easiest and cheapest thermal oil recovery method for heavy oil reservoirs.

 Q. What level of recovery rates could one expect from a heavy oil field both before and after thermal enhancement?

 A. Recovery rates depend on the original in-reservoir viscosity of the crude, its natural temperature and the in-situ pressure: one would expect a non-enhanced recovery rate to range from 1.5 to 10%. After steam injection, one would expect to be able to produce between 50 and 60% of the original oil in place (OOIP).

 The most recent innovation, which occurred in the early 1980s, was the development of steam assisted gravity drainage (SAGD). This has only become possible due to the relatively recent ability to accurately and consistently drill horizontal well pairs into reservoirs.

 Q. I understand that you have done a great deal of work on HO thermal oil recovery from fractured carbonate reservoirs. What particular issues relate to fractured carbonates?

 A. In Turkey, we have undertaken a great deal of work on these types of reservoirs examining, in particular, how both horizontal and vertical fractures, as well as the steam injection using horizontal well pairs, affect oil recovery rates and efficiencies. The primary recovery from this type of reservoir is usually based upon the original reservoir temperature and pressure which allows the heavy oil to flow from the pores into the minor fractures, then into the major fractures and finally into the production well bore.

 However, although the manner whereby the heavy oil passes to the production well is understood, the primary production rates are still extremely low at between 2 and 5%. In order to improve this recovery rate we have to resort to steam recovery. As the injected steam passes from the injection well along both the major and minor fractures, it forces the heavy oil that is contained within the fractures towards the production well, as well as transferring its heat to the unfractured rock.

 However, although these two processes continue in parallel, for this to be effective, it must be properly controlled to ensure a rate that is high enough to force heavy oil along the fractures but not too high that the rock matrix is left unheated.

 Q. How do you control this?

 A. By altering various parameters such as the steam injection rate, the temperature and pressure of the steam, as well as the actual distance between the horizontal injection and horizontal production wells (averaging 5m). What has been shown is that it is the pressure differential between the two wells that is important. If the pressure differential is too high "smooth growth" does not occur in the steam chamber, as the pressure tends to be dissipated as it widens the existing fractures. If it is too low, although the temperature of the heavy oil within the matrix of the formation will rise, the flow between the two wells will be poor.

 Q. What is likely to be the next major advance in thermal recovery?

 A. Some universities and research centres are working on different types of steam injection and in-situ combustion methods. For example, Steam Alternating Solvent (SAS) injection method, and Liquid Addition to Steam Enhanced Recovery (LASER) method which uses hydrocarbons.

 In both of these processes a cocktail of liquid hydrocarbons known as C5+ (usually consisting of at least propane and butane) are added to the steam. The exact composition of this cocktail is determined by the reservoir type. This liquid is designed to dissolve any hydrocarbons which could impede flow along the fractures, thus providing a smooth fracture-path.

 In the SAS method, injection alternates between steam and propane. For example, we will inject steam for six months followed by three months of propane injection as the solvent. The periods of injection are quite considerable, but their lengths are arrived at by experimental trial-and-study.

 In the LASER method these hydrocarbon solvents are added to the steam which is continually injected.

 In addition, there are a number of variations on the steam or combustion methods including: toe-to-heel air injection (THAI), toe-to-heel steam flooding (THSF) which is like THAI except one uses steam instead of air, and top-down combustion where the flame front forces the heavy oil down to a lower collection (i.e. production) well.

 Initial recovery using thermal recovery is about 40% of the original oil in place (OOP). However, with the LASER system, this is raised by a further 20% but unfortunately not every heavy oil formation is suitable for this treatment.

 Q. Why is thermal oil recovery of heavy oil deposits via the combustion method not universally employed?

 A. The combustion method is being used in India, Romania and Indonesia. The combustion injection method was first proposed in the early 1960s with experimental work and field studies being carried out from then until the mid-1980s. But combustion enhancement should always be the last stimulation method to be considered. Firstly, the act of combustion destroys the reservoir and, therefore, you only get one "hit" at extraction. Secondly, it is very difficult to control the flame front once the process has started: you can alter it by increasing or reducing the quantity (and quality) of the air you are injecting, but this is very much a hit-and-miss affair.

 This application can only be effective with the use of observation wells to monitor the behavior and location of the flame front. In addition, you need to ensure that greenhouse gases created by the combustion are not allowed to escape from the reservoir. Indeed, the same is true of any heavy metals which may have been altered and vaporized sub-surface.

 However, my personal view is that the combustion method should always be the thermal oil recovery method of last resort.

 Q. Has much of the progress being made in thermal oil recovery of heavy oils been due to the need to address the requirements of the offshore industry?

 A. In the UK Continental Shelf, there are 10 billion stock-tank barrels of heavy oil waiting to be extracted. By itself, this is a significant incentive, but if you can increase the overall recoveries by 40%, these reserves become even more attractive and it is for this reason that oil companies are pursuing their heavy oil offshore initiatives with such vigour. I believe that downhole steam generators, once they have overcome their mechanical vulnerabilities, will prove to be the step-change that offshore operators are seeking. However, it is worth noting that these devices still need a plentiful and reliable supply of fresh water, to use sea water in these steam generators would place further pressure on these devices. There is a lot more work that needs to be done here, and I am confident that, with the aid of universities and other research establishments, that the resources contained within these offshore heavy oil fields can be harvested.

 Q. What will be the next leap in heavy oil production technology?

 A. In the next ten years steam injection will still be the major method for thermally enhancing heavy oil reserves, with some combustion enhancement. There will be a growth in multilateral applications where several horizontal injection wells will come off a single horizontal bore hole, with several production wells likewise coming off a single production bore hole. I do not think we will be looking at a single universally employed thermal oil recovery method, but rather choosing from a menu of various methods.

 Q. Steam injection methods often cause environmental issues, particularly the CO2 associated with surface steam generation. What is being done to mitigate this?

 A. A great deal of work still needs to be done on the potential for storing CO2 in depleted conventional oil reservoirs. I know that many people feel that CO2 can be used as a driving force to increase production in heavy oil reservoirs, but unfortunately the chemistry and the physics of heavy oil and their reservoirs, simply do not match this aspiration. Nevertheless, CO2 storage is a possibility, but it needs to be captured and transported in sufficient quantities to make a meaningful environmental contribution. However, my view is that environmental issues will be addressed with current and future technology, as long as someone will pay for it.