Electromagnetic Heating Method To Improve Steam Assisted Gravity Drainage

Performance of multiple thermal fluids assisted gravity drainage process in post SAGD reservoirs

In the steam assisted gravity drainage (SAGD) process, a special form of steam flooding, the movement of oil to the production well is caused by gravity forces and is approximately parallel to the interface which forms the boundary of a growing, steam saturated zone known as the "steam chamber". SAGD results in a complex interaction of geomechanics and multiphase thermal flow in cohesion less porous media. Changes in fluid pressure and temperature result in changes in stress and deformations that affect formation shearing and absolute permeability. For thermal recovery projects undertaken in Alberta oil sand deposits, the most intense geomechanical monitoring program was completed during the Phase A SAGD trials at an Underground Test Facility constructed northwest of Fort McMurray, Alberta, Canada. As part of the geomechanics program of the Phase A trials, an extensive laboratory testing program was conducted to examine the thermomechanical properties of oil sands and its intraformational shales and the underlying limestone. The testing program comprised thermal expansion, thermal conductivity, compressibility, stress-strain, strength and gas evolution tests. Selected results of this testing program are presented and discussed. Particular attention is paid to the relevance of these thermomechanical properties to the SAGD process. To illustrate the impact of formation property values on the SAGD process, the results of numerical parametric analyses are presented and discussed. These results, linked back to the laboratory determined properties and compared with field measured formation response, provide substantial insight into the behavior of unconsolidated heavy oil deposits for SAGD thermal recovery projects. In particular, increases in absolute permeability of 30% to 50% may occur in "cold" regions of the reservoir in "front" of a growing steam chamber. Introduction A special form of steam flooding, known as steam assisted gravity drainage (SAGD), has been developed to provide a process which could recover more oil than is possible by conventional steam flooding processes. In the steam assisted gravity drainage process, the movement of oil to the production well is caused by gravity forces and the geometry is such that the oil moves approximately parallel to the interface which forms the boundary of a growing, steam-saturated zone known as the steam chamber. The SAGD process results in a complex interaction of geomechanics and multiphase thermal flow in cohesionless porous media. The geomechanical response of an oil sands reservoir to fluid pressure changes or to temperature changes results in stress and deformations that affect formation shearing, hydraulic properties such as absolute permeability and the stability of underground openings (uncased wells, tunnels and shafts). A temperature increase causes thermal expansion of the sand grains and sand structure. A pore pressure increase during steam injection decreases the effective confining stress. For an anisotropic in situ stress state in the reservoir, pore pressure injection will also generate shear stresses and shear strains in the sand structure. These processes combine to result in a net change in reservoir pore volume and permeability. Most reservoir models used in simulating the steam assisted gravity drainage process do not account for the geomechanical responses described above. Several important parameters which affect process performance are however, directly impacted by the geomechanical response of the reservoir. Porosity is directly proportional to the bitumen production yet porosity can be altered due to shear induced volume changes or changes in effective confining stress. Absolute permeability of the reservoir affects the drainage of fluids from the steam front and therefore the frontal advance rate and the production rate; it is one the most important parameters in the simulation of the SAGD process. Stress change induced volume changes within the reservoir, especially within non-heated zones, will result in changes in absolute permeability. P. 485^

Over 80% of the vast reserves of Alberta's oil sands can be produced only by using in situ recovery methods. Among them, which is likely the most efficient and important, is the Steam-Assisted Gravity Drainage (SAGD) process. Numerical simulation allows for a practical way of predicting reservoir performance using the SAGD process during the whole field development cycle. However, in the earlier stages of development studies, when it is necessary to undertake preliminary engineering design, estimate reserves, evaluate the project against other SAGD prospects, as well as consider the uncertainty of some reservoir parameters, it may not be feasible to do a detailed simulation study due to the long computational time involved in a SAGD process simulation. Under these circumstances, a method for predicting reservoir performance using a simple statistical model that can approximate the reservoir simulator over a given range of some important input parameters is a good approach to provide the means of comparison and preliminary predictions without resorting to numerical simulation. The purpose of this work is to use 'experimental design' techniques to develop a response surface that can predict SAGD performance without the expense of doing simulation. A preliminary screening study was done in order to select the most influential variables on SAGD performance. The variables used for that purpose include reservoir rock/fluid properties, such as reservoir thickness, porosity, vertical permeability, horizontal-vertical permeability ratio, methane content, rock thermal conductivity, initial oil saturation and bitumen viscosity, along with SAGD design and operating variables, including spacing between injector/producer, operating pressure, preheating period, maximum steam injection rate and SAGD well pattern spacing. In a second stage, the influential variables were used to create a statistically significant correlation by using the experimental design method and response surface techniques. This simple model allows the prediction of the SAGD performance in terms of maximum net present value (NPV) over 15 years of project life, for a given range of the most influential parameters. Introduction Numerical simulation of complex systems such as SAGD processes require long computational times due to the compositional nature and transient temperature behaviour of the models used in the solution. Longer simulation times lead to either a delay in the decision-making process or to biased forecasts and sub-optimal decisions, since unpractical times would be required to span all possible scenarios in which a SAGD process can be developed. This is particularly important at the earliest field development stages when the high uncertainty of some reservoir and operational parameters is a significant constraint. Transference of uncertainty from the reservoir and operational parameters to the forecast variables during a SAGD process using numerical simulation is almost an impossible and very expensive task. To overcome this situation, engineers need simple models to predict SAGD performance. As an alternative, this work proposes a "Response Surface Correlation" generated by experimental design techniques and response surface methodology. Such a correlation will substitute the reservoir simulator in a given operating domain in order to account for all necessary cases needed to quantify and transfer the reservoir uncertainty to a SAGD performance variable.

The steam assisted gravity drainage (SAGD) process has proven to be an effective thermal recovery method for heavy oil and bitumen production. Recently, some innovative techniques based on the background SAGD operation have been applied such as conventional SAGD, Fast-SAGD, Hybrid SAGD, FA-SAGD. However, there has been much dispute over the question of economical efficiency due to high capital investment, operating costs, and the fluctuation of oil and gas prices. The integration of economic and technical aspects for SAGD performance plays an important role in field operation. Main problems to solve are how to design optimal operating conditions for a reasonable steam requirement with certain injection pressure to maximize economic feasibility under reservoir conditions.The previous literatures implemented sensitivity analysis and optimization of SAGD performance by classical methods based on numerical simulations lead to a lack of confidence level and ignored interactions effects between considered parameters, which may cause low efficiency issues in a field operation. In addition, the SAGD economic model in previous studies have not fully information with limited consideration on few factors. These restrictions can be avoided by the application design of experiment and response surface methodology to determine the optimal operating conditions for the production prediction. Then, discontinuous SAGD technique was operated to control the amount of injected steam at several specific injection time intervals.This study represented that the discontinuous SAGD performance is applied to three major formations of Alberta’s oil sands. The results showed that both oil recovery factor and economic profit are much higher than other techniques, especially the effective at deeper burial reservoirs of Clearwater and Bluesky formations. Moreover, amount of injected steam and water cut reduced significantly to cause lower operating costs as steam cost, led to increase NPV as well as minimal environmental damages.

In steam assisted gravity drainage (SAGD) process, accumulation of non-condensable gases at the edges of the steam chamber creates a resistance to heat transfer between hot steam and cold bitumen, thus slowing down growth of the steam chamber. Efficient removal of these gases from the steam chamber can substantially accelerate the recovery process. Typical practice in SAGD is to use steam splitters and strive for a relatively uniform pressure in the horizontal part of the well, which allows for even distribution of injected steam into the reservoir. In convective SAGD process, a significant pressure gradient is deliberately created along the horizontal length of the injector well by tailoring the well completion design. Enhanced flow resistances can be fashioned by using finned tubes, static mixers, flow constrictions or simply using tube sections with varying diameters. A complementary placement of resistances in the producer well prevents short-circuiting of steam. Pressure gradients created in the injector well are translated on to the reservoir, thus allowing for a sweep of non-condensable gasses from the steam chamber. In reservoir simulation studies, a novel convective SAGD process has shown significant improvement in oil production, with 20% higher peak production rates as compared to traditional SAGD while facilitating removal of non-condensable gases in excess of 90% from the steam chamber over the life of the well. Since fluids in the reservoir can now also move along the length of the wells, convective SAGD demonstrates a distinct advantage over traditional SAGD in heterogeneous reservoirs as horizontal barriers to flow can now be overcome with time. Currently, a field pilot is being pursued at Foster Creek to test the validity of convective SAGD process.

Rich solvent - Steam assisted gravity drainage (RS-SAGD): An option for clean oil sands recovery processes

The LD5-2N block is a typical heavy oil reservoir in Bohai offshore oilfield, and the viscosity of crude oil for this block at reservoir condition is about 10000mPa.s. Therefore, the conventional exploitation method of water flooding or chemical flooding will be not suitable for this block, and the thermal recovery should be considered. Using the method of numerical simulation, the steam assisted gravity drainage (SAGD) process for this block is investigated in this paper. Firstly, a sensitivity analysis process of reservoir properties and fluid parameters is con- ducted, e.g., reservoir thickness, oil viscosity, permeability, the vertical-horizontal permeability ratio etc. Then, on account of the shale cases in this block, an orthog- onal test is carried out to study the influences of shale barriers on SAGD process. Results indicate that the parameters of reservoir thickness, reservoir permeability have a significantly influence on the recovery rate of SAGD process. For a SAGD process, the reservoir thickness should be greater than 20m. With the increase of vertical permeability, the expanding rate of steam chamber is on a rise, and thus the recovery rate of SAGD process is increased. The bottom water will reduce the oil recovery by about 10 20%. Furthermore, the existence of shale barrier also has a tremendously influence on the drainage process, especially for the recovery rate. This investigation could be used for the application of SAGD technique in the similar heavy oil reservoirs.

Determination of binary diffusion coefficients between hot liquid solvents and bitumen with X-ray CT

An investigation is presented on the use of Flow Control Valves (ICVs, FCVs) to control steam placement in the early stages of a Steam Assisted Gravity Drainage (SAGD) process. The two parts of this process that are examined in this paper are the steam circulation preheating period and the early stages up to one year of injection/production in which the steam chamber is beginning to form. Steam injection and production in this and other thermal processes can be difficult to control because steam has a high mobility ratio and tends to establish flow paths that may be difficult to break once established. This is especially pronounced in heterogeneous reservoirs. Two SAGD case studies have been designed that accurately model the initial preheating period in which both wells circulate steam through an inner tubing and outer annulus in order to conductively and, to a lesser extent convectively, heat the region around the well pair in order to establish communication. After this initial circulation period, the wells switch to injection and production. Both cases have the same base configuration but differ in the degree of reservoir heterogeneity. In the injection well, ICV devices are placed to control steam/water flow through the outer screens. In the producer, FCV valves are used to flatten the production profile along the well. Two methods are examined to change valve apertures. One uses proportional-integral-derivative (PID) controllers while the second applies an optimization algorithm directly on each individual connection productivity index. A preliminary investigation is presented here into using feedback controllers and optimization with instantaneous reservoir parameters to improve a SAGD process in the presence of reservoir heterogeneity.

The steam assisted gravity drainage (SAGD) process requires high energy input to maintain the continuous expansion of the steam chamber for achieving high oil recovery. In the late stage of SAGD operation where the oil rate is low and the heat loss is high from a mature steam chamber, maintaining steam chamber pressure with a lower steam injection is the key to maintaining the economic oil-to-steam ratio (OSR). Both laboratory studies and field tests have demonstrated the effectiveness of adding a non-condensable gas (NCG) to the SAGD steam chamber for improving the overall thermal efficiency. In this study, a multi-well reservoir model was built based on the detailed geological description from an operating SAGD project area, which contains thick pay and top water. Grounded with the history matching of more than 20 years of production using CSS (cyclic steam stimulation) and SAGD as follow-up process, the model was applied to optimize the operating strategies for the late stage of SAGD production. The results from this study demonstrated that the co-injection of steam with CO2 or the injection of CO2 only has potential to improve the OSR and reduce emissions by more than 50% through the improvement in steam-saving and the storage of CO2. The results from reservoir modeling indicate that, with the current volume of a steam chamber and an operating pressure of 4.0 MPa, about 55 sm3 of CO2 could be sequestrated and utilized for producing 1.0 m3 of oil from this reservoir through the replacement of a steam injection with CO2 in the late stage of SAGD operation.

In reservoir simulation, the fluid composition is usually assumed uniform for the whole reservoir, while in many reservoirs, oil and gas composition changes with depth. This phenomenon which is known as compositional grading could be significant in heavy and super heavy oil reservoirs. In these reservoirs, biodegradation and asphaltene precipitation are considered as the main reasons behind this phenomenon. Compositional grading in heavy oil reservoirs could affect fluid viscosity and vaporizing–condensing mechanism in steam-assisted gravity drainage (SAGD) operations. In this paper, through a simulation study, one of the Iranian heavy oil reservoirs which have a significant compositional grading was selected to investigate the effect of compositional grading on the performance of simulated SAGD method. The reservoir is a fractured carbonate reservoir, and its compositional grading is maintained because of the lack of convection inside the reservoir. To verify the importance of compositional grading, the performance results of the SAGD method for compositional grading case were compared with that of uniform composition case. The result showed that ignoring compositional grading would lead to underestimation of ultimate recovery in the fractured model. The study of SAGD process in a non-fractured reservoir model showed that considering compositional grading has an insignificant effect on SAGD performance.

ExxonMobil and its Canadian affiliate, Imperial Oil Resources, are actively developing the next generation of solvent-aided and solvent-dominated heavy oil recovery processes. While these new recovery processes possess multiple environmental and technical advantages relative to traditional heavy oil recovery processes, there are a variety of challenges that must be addressed and overcome before commercial application. One especially promising technology is the Solvent Assisted – Steam Assisted Gravity Drainage (SA-SAGD) process. In the SA-SAGD process, a light hydrocarbon solvent (diluent) is injected along with dry steam in a dual horizontal well SAGD configuration. An integrated research program has been implemented in order to progress the SA-SAGD technology from the laboratory to the field and to better quantify the benefits of SA-SAGD over SAGD. This integrated research program includes fundamental laboratory work, advanced numerical simulation studies, scaled physical laboratory models, and a two well-pair field pilot. In this paper, we review the scope, technical challenges, and key learnings from the laboratory, numerical modeling efforts, and the field pilot. Each individual component of the research program is important and provides unique and useful information concerning the SA-SAGD process. Given the technical and economic challenges of solvent-assisted thermal heavy-oil processes, these types of fully integrated research programs are essential in order to successfully progress new technologies from the laboratory to the pilot scale and ultimately to the commercial scale. Ultimately, the program is targeted at developing reliable commercial predictive capabilities that have been validated against both laboratory and field data, for application to a wide range of heavy oil reservoirs, operating conditions, and development plans.

For oil sands assets having bitumen resources located near the ground surface, geomechanical assessments of caprock performance during steam-assisted gravity drainage (SAGD) operations have become increasingly important. These assessments need to determine and demonstrate whether the caprock can effectively withstand the induced stress and strain loadings from the SAGD operation throughout the life of the development. The importance of caprock integrity for SAGD developments was realized following the loss of caprock containment at the Total E&P Canada Ltd., Joslyn Creek SAGD project in 2006. In light of this failure, the Alberta Energy Resources Conservation Board (ERCB) stipulated a series of response activities to address caprock integrity, including the requirement that pilot and commercial SAGD projects in Alberta need to conduct a geomechanical assessment of caprock integrity as part of the application process. The authors completed a geomechanical simulation study of the Clearwater Formation caprock performance at a proposed, shallow, low pressure, SAGD (LP-SAGD) pilot project located southeast of Fort McMurray, Alberta, Canada. For this investigation, a 3D, coupled, reservoir and geomechanical simulation was conducted forecasting 10 years of asset response to the maximum operating pressure of 1,000 kPaa. The geomechanical response of the caprock to temperature changes, increased pore pressure and the induced stress and strain fields from the steam chamber was simulated as part of the caprock integrity assessment for the pilot project. This paper presents the results of this simulation study and the uncertainties and risks associated with evaluating caprock containment of SAGD operations using numerical methods. The results of key geomechanical parameters, such as minimum principal effective stress, shear stress level, factor of safety and surface displacement are presented. A summary of the post-failure analyses of caprock containment at the Joslyn Creek SAGD project is presented.

1. Abstract Successful application of gravity drainage process, facilitated with steam injection, using horizontal wells in various field tests, especially within Canada, indicates that high recovery factor and also economical steam to oil ratios are achievable. Steam Assisted Gravity Drainage recovery scheme was theoretically developed, pilot tested and commercialized in Canada, however, there are still several technical challenges to be solved in this process. The pore-scale events of heavy oil recovery in SAGD process are not yet well understood to the extent of incorporating pore-level physics of the process into mathematical models. Investigation of the physics of fluid distribution and flow behavior in porous media for SAGD process at the porescale is expected to result in significant improvement in understanding the macroscopic phenomena observed in either laboratory or field scale. The main objective of this paper is to visually investigate and to document the pore-scale events of the SAGD process using glass micromodel type of porous media. SAGD experiments were carried out in micromodels of capillary networks etched on glass plates which were initially saturated with heavy oil. Experiments were conducted in a vacuum chamber in order to reduce the excessive heat loss to the surrounding environment. Initial results indicate that when the heavy oil-steam interface is established, gravity drainage process takes place through a layer of pores, with a thickness of 1 - 6 pores, in the direction perpendicular to the interface. The interplay between gravity and capillarity forces results in the drainage of mobilized oil. The visualization results demonstrate the phenomenon of water in oil emulsification at the interface due to the local steam condensation. The extent of emulsification depends directly to the temperature gradient between steam phase and cold bitumen. Other pore-scale phenomena such as film-flow drainage type of mobilized oil, localized entrapment of steam due to the capillarity followed by condensation, steam condensation at the interface due to temperature gradient, and snap-off of liquid films are also illustrated using glass micromodels in pore-level visualization experiments. 2. Introduction Heavy oil and bitumen are of great economic importance to Canada. The quantity of oil in place in the form of bitumen in Canada is as great as that of the conventional crude oil in the Middle East and it is a major Canadian technical challenge to utilize this vast resource efficiently and economically. A recent estimate of the recoverable volume represents only 12% of the volume of bitumen in place, based on the available economic conditions. However, there is considerable potential for this percentage to increase as advances are made in the recovery technologies. Recently, the reserves are estimated to be 28.3 billion cubic meters, made up of only 5.6 billion cubic meters in the surface-mineable areas and 22.7 billion cubic meters for the deeper areas. This total volume is sufficient to satisfy total Canadian demand for crude oil, at current rates, for approximately 250 years [1]. Thermal recovery techniques have been proved to be effective methods of utilizing heavy oil, extra heavy oil, and bitumen considering their in-situ upgrading potential as well as economic considerations. Among the vast spectrum of thermal recovery techniques, Steam Assisted Gravity Drainage (SAGD) seems a suitable recovery candidate especially for the Canadian and Venezuelan unconventional viscous hydrocarbon resources because of their unique unconsolidated lithology and its associated high vertical permeability.

Summary Steam injection is commonly used as a thermal enhanced-oil-recovery (EOR) method because of its efficiency for recovering hydrocarbons, especially from heavy-oil and bitumen reservoirs. Reservoir models simulating this process describe the thermal effect of the steam injection, but generally neglect the chemical reactions induced by the steam injection and occurring in the reservoir. In particular, these reactions can lead to the generation and production of the highly toxic and corrosive acid gas hydrogen sulfide (H2S). The overall objective of this paper is to quantitatively describe the chemical aquathermolysis reactions that occur in oil-sands reservoirs undergoing steam injections and to provide oil companies with a numerical model for reservoir simulators to forecast the H2S-production risks. For that purpose, a new sulfur-based compositional kinetic model has been developed to reproduce the aquathermolysis reactions in the context of reservoir modeling. It is derived from results gathered on an Athabasca oil sand from previous laboratory aquathermolysis experiments. In particular, the proposed reactions model accounts for the formation of H2S issued from sulfur-rich heavy oils or bitumen, and predicts the modification of the resulting oil saturate, aromatic, resin, and asphaltene (SARA) composition vs. time. One strength of this model is that it is easily calibrated against laboratory-scale experiments conducted on an oil-sand sample. Another strength is that its calibration is performed while respecting the constraints imposed by the experimental data and the theoretical principles. In addition, in this study no calibration was needed at reservoir scale against field-production data. In the paper, the model is first validated with laboratory-scale simulations. The thermokinetic modeling is then coupled with a 2D reservoir simulation of a generic steam-assisted gravity drainage (SAGD) process applied on a generic Athabasca oil-sand reservoir. This formulation allows investigating the H2S generation at reservoir scale and quantifying its production. The H2S- to bitumen-production ratio against time computed by the reservoir simulation is found to be consistent with production data from SAGD operations in Athabasca, endorsing the proposed methodology.