A Critical Review of the Status of SAGD: Where Are We and What Is Next?
- As Muatasim Mohammad Al Bahlani (U. of Alberta) | Tayfun Babadagli (U. of Alberta)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional and Pacific Section AAPG Joint Meeting, 29 March-4 April, Bakersfield, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2008. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.6.4 Drillstem/Well Testing, 5.4.10 Microbial Methods, 7.4.3 Market analysis /supply and demand forecasting/pricing, 1.2.2 Geomechanics, 5.6.6 Cross-well Tomography, 4.1.2 Separation and Treating, 1.2 Wellbore Design, 5.3.9 Steam Assisted Gravity Drainage, 3.1.1 Beam and related pumping techniques, 5.5.3 Scaling Methods, 3 Production and Well Operations, 4.1.5 Processing Equipment, 5.4.2 Gas Injection Methods, 5.1 Reservoir Characterisation, 5.2.1 Phase Behavior and PVT Measurements, 5.5.4 Visualization Technologies, 5.5.8 History Matching, 5.1.5 Geologic Modeling, 5.8.7 Carbonate Reservoir, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.1.1 Exploration, Development, Structural Geology, 3.1 Artificial Lift Systems, 5.3.2 Multiphase Flow, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.4.9 Miscible Methods, 5.5 Reservoir Simulation, 5.4.6 Thermal Methods, 1.2.3 Rock properties, 1.6.9 Coring, Fishing, 5.6.11 Reservoir monitoring with permanent sensors, 4.3.4 Scale, 4.6 Natural Gas, 2.4.3 Sand/Solids Control, 5.3.4 Reduction of Residual Oil Saturation
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With around 7 trillion barrels reserves and recent increase in oil demand, there is no doubt that there would be tremendous effort on the development of heavy-oil/bitumen (HO-B) reservoirs in the next decades. Yet the in-situ recovery of HO-B is still not a simple process and there are many technical challenges accompanied with it.
Two major techniques, namely thermal and miscible, have been considered in the HO-B development, along with several other auxiliary methods (chemical, gas, electromagnetic heating etc.) for different well configurations, steam assisted gravity drainage (SAGD) being the most popular among others. Miscible techniques did not yet go to a high commercial level, while thermal techniques have by far a stable foundation in the industry.
Despite remarkable amount of laboratory experiments and computational studies on the thermal techniques for HO-B, especially SAGD, there was no extensive and critical literature review of the knowledge gained over almost three decades. We believe that a critical review of the status of the SAGD process will fill the gap by shedding light on the deficiencies and limitations of the process, further development areas, and new research topics. Specific attention, in this paper, was given to (a) the effect of geological environment on the physics of the process, (b) evaluation of the laboratory scale procedure and results (reasons of residual oil saturation, is it well configuration or pore scale dynamics?) and the reasons of the inconsistency between the lab and field scale performances, (c) problems faced in numerical modelling (capturing the physics of the process, relative permeability curves, dynamics of gravity controlled counter-current flow), (d) evaluation of the pilot and commercial level field applications, and (e) operational and technical challenges.
It is believed that a good compilation of the records produced over three decades will constitute a useful reference for the industry and academic people.
Reservoir heating is essential in heavy/ultra heavy-oil and bitumen (HO-B) recovery. Steam injection is the only proven thermal technique to be used for this purpose and it can be achieved through continuous or cyclic (huff-and-puff) injections. Field experience and simulations studies show that performing these techniques may not be economical and is associated with technical difficulties as the oil gets heavier. For thick and high permeability reservoirs with HO-B, Steam Assisted Gravity Drainage (SAGD) method was proposed by Butler and his friends more than 30 years ago (Butler 1998). Due to increased contact area through two horizontal wells, one being injector and the other being producer, the process was believed to be successful not only from technical point of view but also economical standpoint. Over 30 years period, this technique has been commercialized successfully which led so many to think of it to be a standard technique in HO-B recovery. Obviously, it has some restrictions including the requirement of high vertical permeability and high energy consumption.
Alternatives to this technique have been proposed for unsuitable reservoirs. Those techniques include miscible flooding (VAPEX) or modified versions of SAGD through different configurations of wells or using additives to steam. In any event, SAGD in specific, or using two horizontal well in general for HO-B recovery, appears to be a promising option for the development of HO-B reservoirs if the main requirements for its applicability are met.
Due to its suitability for unconsolidated reservoirs that display high vertical permeability, the SAGD technique has received an attention in the countries like Canada and Venezuela with huge HO-B sand reserves. Remarkable amount of laboratory-simulation studies and limited field cases were reported over thirty years. Very limited number of studies was reported on SAGD in fractured/carbonate reservoirs.
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