The first commercial test of solvents took place in California in 1960 where solvent stimulation was used to increase production of heavy oil. Currently, successful performance of steam injection in horizontal wells suggests the idea of using hot solvent alone or in conjunction with steam to reduce bitumen viscosity. The present study compares the performance of heat, cold solvent, and hot solvent for reducing bitumen viscosity at the pore scale using typical field data.
The governing equations were derived for heat transport by conduction and convection and solvent diffusion and dispersion. The equations were solved in spherical geometry for a droplet of bitumen at different flow rates. In addition to solvent and steam together, equations were derived for a hot solvent. The mass and heat balance equations were solved simultaneously and the viscosity profile was obtained. The performance of different solvents at different temperatures was compared with heat under the same conditions.
The results indicated that hot solvent is much more effective than solvent alone due to the effect of temperature on oil viscosity. It was found that the effect of solvent is much less than that of heat and that the high recovery by heated solvent is directly related to the heat. The time required for cold solvent to reduce bitumen viscosity was much longer compared to conduction-convective heating even at high solvent rates. Hot solvent shows promise compared with conduction-convective heating as a result of the heat contribution.
In spite of the benefits of using solvent, the economics must be considered. This study improves our understanding of the mechanistic behavior of solvent assisted recovery processes and modelling approaches at the pore scale.
Warne, George A. (Canadian Association for the WPC) | Patel, Raj (Imperial Oil) | Rauch, Bruce (Imperial Oil ) | Ali, S.M. Farouq (U. of Calgary) | Moore, Gord (U. of Calgary) | Mehta, Raj (U. of Calgary) | Ursenbach, Matthew (U. of Calgary) | Yeung, K.C. (Suncor Energy Inc.) | Peachey, Bruce (New Paradigm Engineering Ltd.) | Zahacy, Todd (C-FER Technologies Inc.) | Hyne, Jim (Hyjay R&D Ltd.) | Das, Swapan (Suncor Energy Inc.) | Mungan, Nick (Sproule Associates Ltd.) | Masliyah, Jacob (U. of Alberta) | Brady, Kevin (Precision Drilling Corp.)
The JCPT and the Canadian Association for the WPC agreed that itwould be a timely and valued service to readers and delegates to the 17th WorldPetroleum Congress to publish a series of articles reviewing several keypetroleum technologies receiving attention in Canada. Distinguished authoritieson the technologies agreed to contribute short summary articles on Canadianresearch and field experience in specific areas. These articles are included inthis issue:
The Evolution of Imperial Oil's Cold Lake Development by Raj Patel and BruceRauch
Innovative Steam Injection Techniques Overcome Adverse Reservoir Conditionsby S.M. Farouq Ali
Air Injection for Oil Recovery by Gord Moore, Raj Mehta, and MatthewUrsenbach
Suncor's Path to Growth - Oil Sands Projects and Technology by K.C.Yeung
Downhole Oil/Water Separation's Canadian Roots by Bruce Peachey and ToddZahacy
Canada's Recovered Sulphur - In the World Class by Jim Hyne
VAPEX - A Unique Canadian Technology by Swapan Das
Canada - World Leader in Hydrocarbon Miscible Flooding by Nick Mungan
Bitumen Recovery From Athabasca Oil Sands by Jacob Masliyah
Computalog's LWD System Designed for Deepwater Drilling Environments byKevin Brady
Electrical Heating of heavy oil reservoirs has been successfully applied in near wellbore regions. Well stimulations through downhole resistive, dielectric, or induction electric heating systems when applied in suitable reservoirs can triple flow rates for a small additional operating cost. In such cases high-energy conversion ratios such as 10-15 bbls. Of oil for every bbl of oil consumed at the power plant can be achieved. Applications of electric heating can particularly be beneficial in situations where steam cannot be used due to either depth, formation incompatibility, low incipient injectivity, excessive heat losses or existence of thief zones. Additionally, for reservoirs already having a high temperature in the 60-80 degree C and higher range, only a small amount of electric heating-stimulation is enough to increase oil production by an order of magnitude. Some Orinoco reservoirs of Venezuela fall into this category. Heavy oil reservoirs, overlain by heat sensitive permafrost, may also find electrical heating a viable thermal stimulation technique. Electrical heating process has also been adapted to apply in preheat phase of other complimentary processes like VAPEX. The process also has been investigated for hot water flood in deep reservoirs. This paper proposes to use downhole electric systems for stimulating for both vertical and horizontal wells in such reservoirs. Using CMG's thermal simulator-STARS (ref. 7), results of several worldwide investigations are included. A summary of field applications is also presented. In addition, incremental oil recovery vs. energy consumption is tabulated.
Electrical heating tools and subsequent applications can be broadly divided into three different categories based on frequency of electrical current used by the tool (ref 5). (1) Low frequency currents are used in Resistive/Ohmic heating and (2) High frequency currents are used in Microwave heating methods. (3) The Induction tools have the ability to use a wide range of low to medium frequency currents depending on heat requirements and desired temperature.
Electric current from low frequency resistive tools penetrates deeper into the reservoir than from the high frequency RF tools at temperatures below the vaporization point of water, though the temperature of the affected zone may be higher with RF tools. The insitu water provides an ionic conduction path in the resistive heating systems permitting the use of less costly low frequency energy supplies. Induction tools on the other hand produce electromagnetic fields, which induce eddy currents and hysteresis-losses in the casing or liner resulting in heat generation. Thus heated casing or liner provides heat for the near well bore section of the reservoir. These tools are very efficient and Induction heating technology has found its place in a large number of industrial applications. For heavy oil reservoir insitu heating applications, both Resistive and Induction tools have been more widely used as opposed to RF tools. This paper discusses only Formation-resistive and Induction heating methods.
Low Frequency Heating: In this method, low frequency current, using ionic conduction mechanism, is made to travel through interstitial water present in the reservoir matrix system. Electrical energy is converted into heat energy through associated ohmic losses in the formation. The overall effect of the heat generation is to reduce the pressure drop near the wellbore by decreasing oil viscosity and improving oil mobility. The bulk electrical conductivity in formation can be obtained from the Archie and Humble's relation (ref.2 ) given below. It demonstrates how for interstitial water is essential.
The temperature dependence of the water resistivity is given by:
Where Rw is in ohm-meters and T is in degrees Kelvin.
Experiments on initial stages of the steam-assisted gravity drainage (SAGD) process were carried out, using two-dimensional (2D) scaled reservoir models, to investigate production process and performance. Expansion of the initial steam chamber, its shape and area, and its temperature distributions were visualized with video and thermal-video pictures. The relationship between isotherms and steam-chamber interface was investigated to study the drainage mechanism. Temperature at the expanding steam-chamber interface was observed to remain nearly constant at close to 80°C. The effect of vertical spacing between the two horizontal wells on oil recovery was also investigated. For the Conventional SAGD case, oil production rate increased with increasing vertical spacing between the wells; however, the lead time for the gravity drainage to initiate oil production became longer. The results suggest that vertical spacing between the wells can be used as a governing factor to evaluate production rate and lead time in the initial stage of the SAGD process. Based on these experimental results, the SAGD process was modified; the lower production well was intermittently stimulated by steam injection, in conjunction with continuous steam injection in the upper horizontal injector. With the modified process (named SAGD-ISSLW), the time to generate near-breakthrough conditions between two wells was shortened, and oil production was enhanced at the rising chamber stage compared with that of the Conventional SAGD process.
Many mobile heavy oil reservoirs in Saskatchewan and Alberta are unsuitable forthe application of thermal recovery methods, such as steam injection, for anumber of reasons including formation thicknesses of less than 10 m. Oilrecovery from such reservoirs can be accomplished by the use of nonthermalmethods, among which chemical flooding has considerable importance. This paperdiscusses recent laboratory results using chemical flooding techniques. At thesame time, limitations of such methods, limited field experience in heavy oilformations, and possible improvements are also considered. Among the chemicalflooding methods, alkaline and surfactant flooding techniques are moreimportant, partly because the chemicals involved are less expensive, and alsomuch has been learned from past experience in laboratory and field. Thelaboratory studies discussed consisted of surfactant floods and huff n'puff oftwo Lloydminster heavy oils. The recoveries in the floods were as high as 33%.The other recovery method discussed involved cyclic stimulation using twosurfactants. Oil recoveries as high as 12% were achieved. Though recovery wasow, such an approach can be cost-effective in special circumstances.