Application of the SAGD to an Iranian Carbonate Heavy oil reservoir
- Behnam Sedaee Sola (Amir-Kabir U of Technology) | Fariborz Rashidi (Amir-Kabir U of Technology)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional/AAPG Pacific Section/GSA Cordilleran Section Joint Meeting, 8-10 May, Anchorage, Alaska, USA
- Publication Date
- Document Type
- Conference Paper
- 2006. Society of Petroleum Engineers
- 5.1.5 Geologic Modeling, 5.7.2 Recovery Factors, 5.2 Reservoir Fluid Dynamics, 4.3.4 Scale, 1.8 Formation Damage, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.4.6 Thermal Methods, 5.3.9 Steam Assisted Gravity Drainage, 5.8.7 Carbonate Reservoir
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Steam injection is the most important thermal enhanced oil recovery; while in this method Steam-Assisted Gravity Drainage (SAGD) is a very promising recovery process to produce heavy oils and bitumen. The method ensures both a stable displacement of steam and economical rates by using gravity as the driving force and a pair of horizontal wells for Injection/production.
SAGD in Sandstone heavy oil Reservoirs has been characterized quite well over the last years. However, there is huge carbonate heavy oil reserves in the world which their production can be enhanced by thermal recovery processes, especially by steam injection.
In this study, Application of SAGD to an Iranian heavy oil carbonate reservoir with low matrix permeability has been investigated. Field-Scale 3-D and simulation models were constructed by using commercial softwares and by thermal simulators to investigate SAGD performance in this reservoir.
The model was further applied to a fractured system and effects of fracture and matrix permeability, Vertical well spacing between producer and Injector and Length of the horizontal section of the injection well on the performance of SAGD process were studied. By comparison with other thermal methods results showed that SAGD can be used as a better EOR method for this heavy oil carbonate reservoir.
Heavy oil is often over looked as a resource because of the difficulties and costs involved in its production. But , the more than 6 trillion barrels of oil in place attributed to the heaviest hydrocarbons, triple the amount of world reserves of conventional oil and gas, deserve a closer look.
While other factors such as porosity, permeability and pressure determine how a reservoir will behave, it is the oil density and viscosity that dictate the production approach an oil company will take.
On the other hand, the increasing costs of discovering new oil fields and finite limits of conventional oil reserves provide active incentive for more efficient recovery methods. Research is currently being done to maximize oil recovery while minimizing the cost of the used fluids.
Thermal enhanced oil recovery methods that have been applied in the field include hot water drive, steam injection and In-Situ combustion. Steam injection is a more effective method than hot water drive, on account of the latent heat of vaporization that can be harnessed from the steam. For this reason, hot water drive is very rarely used nowadays. Due to wellbore heat loss, steam injection may not be feasible beyond a depth of some 3000 ft. For deeper reservoirs; in-situ combustion may be a more suitable thermal EOR method. However, currently by far, steam injection is the most widely used thermal EOR method.
Heavy oil and tar sands are important energy sources which occur in many countries. The largest reserves are in Canada (3 trillion bbls), Venezuela (2 trillion bbls), USA (over 500 billion bbls), Russian (over 600 billion bbls) and Middle East (over 5300 billion bbls). In Iran, according to the last studies, there are more then 80 billion bbls heavy oil. This kind of Iranian oil is defined as oil with API less them 20° and movable in reservoir. Assuming an ultimate recovery factor of 15% for heavy oil and extreme heavy oil, and 33% for conventional oil, the reserves are nearly same. But ultimate recovery factor for heavy oil could be much higher. At present, world wide heavy oil production is around three million bbl/day (about 4% of total oil production).The best key to producing heavy oil is to reduce oil viscosity, and that is best accomplished by heat. Among the many thermal methods for heavy oil recovery, steam injection maybe the most successful method. This method is responsible for 80% of thermal heavy oil production. [1, 2, 3, 4]
Fractured reservoirs are estimated to contain 25-30% of the world supply of oil. Many of these reservoirs contain heavy oil or tar that can only be recovered by a thermal recovery technique.Field test results indicate that steam injection has good potential for fractured reservoirs. Fractures can also be created artificially during steam injection into reservoirs containing viscous crudes and tars. Physical processes taking place during steam injection should be understood thoroughly, and reliable models should be developed, for effective and economic recovery of oil from fractured systems.
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