Steam Assisted Gravity Drainage Process Research Articles

Cleaner production from Steam-Assisted Gravity Drainage using seismic-based automated control

Besides cost, one major challenge facing the recovery of bitumen from the Canadian oil sands is the amount of greenhouse gas (GHG) emitted to the environment from the Steam-Assisted Gravity Drainage (SAGD) process. The situation is worse in reservoirs that are considered difficult-to-produce due to their geology. This has placed social pressures on oil sands operators to find cleaner, more environmentally friendly ways to produce oil from these reservoirs. The research documented here examines the combined use of flow control devices, specifically outflow control devices (OCDs) in the steam injection wells, and automated control to improve SAGD steam chamber conformance thereby raising the recovery process' efficiency and lowering its environmental impact. The combination of process control and flow control devices in the steam injection well is novel and offers a new method to reduce environmental impact of the process. The results show that there is an increase of the cumulative oil produced by up to 10.7% and 6.16% when compared to the base and OCDs without control cases, respectively, after 6 years of operation. There has also been a reduction of up to 11.7% and 6.5% of the cumulative steam-to-oil ratio, and thus the GHG emissions to produced oil ratio, compared to the base and OCDs without control cases, respectively. The results confirm that cleaner production is possible for SAGD by using seismic-based control together with OCDs in SAGD operations.

Coinjection of C6, C7, and CO2 with steam to improve low-pressure SAGD process

Steam assisted gravity drainage (SAGD) is one of the most widely used processes of thermal recovery for heavy oil. Investigating the effectiveness of solvent coinjection with steam is an important aspect in the optimisation of SAGD process. So far, however, the effects of using CO2 have not been closely examined. This study sheds light on the addition of hydrocarbon solvents with CO2 which reached earlier maximum ultimate oil recovery (90%) than that for other solvents coinjection. This study shows that solubility of C6, heat loss reduction and CO2 diffusion, are the main recovery mechanism in enhancing oil recovery. The present study highlights the steam propagation in the presence of C6 and CO2 and its relation to enhancing oil recovery. It is interesting to observe that physical properties of the injected fluid reduce the energy consumption. Another finding is that solvent coinjection leads to stable subcool, hence increase oil recovery.

Experimental and numerical simulation studies on effects of viscosity reducers for steam assisted gravity drainage performances in extra-heavy oil reservoirs

Steam-Assisted Gravity Drainage (SAGD) has been demonstrated as an effective process for recovering extra-heavy oil. However, large volumes of steam are required to heat the viscous oil, resulting in high consumption of natural gas and water, which affects its economic benefit. Therefore, research has long focused on improving the SAGD performance. In this study, a viscosity reducer (VR) assisted SAGD (VR-SAGD) process is systematically examined by experiment and numerical simulations based on an extra-heavy oil sample from a commercial SAGD block in Xinjiang oil fields, China. A scaled two-dimensional (2D) VR-SAGD experiment is carried out using a scale model to study the mechanisms of production dynamics and to observe the steam chamber development phases of the VR-SAGD process. A history match is conducted based on the 2D experimental data, and the recovery mechanisms of VR-SAGD are discussed. Heterogeneity in terms of barriers sandwiched in the pay zone is studied, and operational parameters are optimized based on the history match results. The 2D physical simulation results show that VR-SAGD accelerates the oil rate by a factor of 1.74 and reduces the instantaneous steam-to-oil-ratio by 49.7%. The VR co-injected with steam propagates in advance and accumulates at the front of the steam chamber and around the barriers to accelerate the effect of viscosity-reduction and reduce the heat loss to the overburden. Numerical simulation results indicate that the optimum time for VR injection is during and after the phase when the steam chamber expands sideways. The optimized VR/steam volume ratio and production/injection volume ratio are 1:9 and 1.2:1, respectively. The VR-SAGD process shows good potential to improve post-SAGD performance and reduces steam consumption in extra-heavy oil reservoirs.

Two-phase and three-phase equilibrium K-values for modelling of non-condensable gas Co-Injection processes

To improve the efficiency of Steam Assisted Gravity Drainage process (SAGD), a small amount of non-condensable gases can be added to steam. The non-condensable gas creates an insulation film at the top of the steam chamber as a result of gas accumulation. This could prevent heat loss to the overburden, increase steam chamber propagation in the lateral direction, and consequently improve the SAGD performance. Field-scale modelling and simulation of non-condensable gas injection in a hybrid SAGD process requires a comprehensive numerical model that includes variety of mechanisms involved in the processes. During the steam/non-condensable gas co-injection, the non-condensable gas may partially be dissolved in bitumen and water, accounting for a portion of gas production from the chamber. Therefore, in order to accurately model the non-condensable gas injection process, the partitioning of the gas among the phases (oleic and aqueous) must be well understood.The most significant challenge of modelling multi-phase equilibrium in gas/bitumen/water systems is the lack of three-phase equilibrium data. This study presents a methodology to generate two-phase and three-phase K-values from the experimental solubility data. The data for binary systems at certain temperatures and pressures is translated into equilibrium K-values. The K-values were calculated either from a correlation representing the phase behavior data or from an equation of state coupled with Henry's law. Then, the generated two-phase and three-phase K-values were directly implemented in reservoir simulators to account for component partitioning in different phases. The results indicate that the generated K-values would be applicable for different types of bitumen.

Thermodynamic and Economic Analysis Between Organic Rankine Cycle and Kalina Cycle for Waste Heat Recovery From Steam-Assisted Gravity Drainage Process in Oilfield

A thermodynamic and economic comparative analysis are presented for waste heat recovery (WHR) from the heavy oil production with steam-assisted gravity drainage (SAGD) process employing organic Rankine cycle (ORC) and Kalina cycle (KC). The liquefied natural gas (LNG) cold energy is employed as the cold source. Thus, a combined cooling heating and power system is proposed. The effect of key parameters on thermodynamic performance is investigated. The results showed that increasing the turbine inlet temperature (TIT), ORC is more appropriate for WHR in SAGD process than KC, but KC provides better energy use and exergy efficiency, while the reverse situation occurs when the evaporation pressure is increased. The compression ratio has little effect on the cold exergy recovery efficiency of the refrigeration cycles. In addition, the total exergy destruction and the total WHR efficiency in the combined SAGD/KC are slightly higher than these in the combined SAGD/ORC. Moreover, for the TIT below 180 °C and the evaporation pressure above 6 MPa, the SAGD/KC can obtain more energy return on investment (EROI) than SAGD/ORC. The results obtained through economic analysis show that the use of the SAGD/ORC is more economical. Through the thermos-economic comparison of the two combined systems, it helps to choose different combined cycles according to the different actual operation, which can facilitate the future engineering applications.

Analytical modelling of steam chamber rise stage of Steam-Assisted Gravity Drainage (SAGD) process

When steam is injected continuously in a SAGD operation, a steam chamber starts to develop in three stages; rise, lateral spreading and confinement, as observed in the field and laboratory experiments. The physics of chamber development in the first and the two last stages is different and thus modelled separately. Nearly all of the available theoretical analyses of SAGD are concerned with the lateral spreading stage of the steam chamber development with the exception of a few works which aim to determine rise velocity and oil rate. The rate of the upward growth of the steam chamber has a profound effect on the SAGD performance, because as the chamber reaches the top of the reservoir heat loss starts to play a significant role in the thermal efficiency of the process.During the rise period, as the steam chamber grows upwards, oil drains downwards and so the process at this stage must account for to the frontal instability between steam and the liquid phases in the system. Stability is affected by factors such as the flow direction, gravity, and viscosity difference between gas/steam and liquid phases. Steam condensation, on the other hand, has a stabilizing effect.In the present model, the rise velocity and the steam chamber height were calculated by combining volumetric oil displacement with Darcy oil rate considering the indirect effect of frontal instability. The model is extended to predict oil production, heat or steam injection rate, heat consumption and CSOR during this phase. Moreover, estimates of injected steam sweep efficiency and the angle between the steam chamber and the horizon are achieved. The model results show an increase in rise velocity with temperature and permeability. Also, the calculated oil production rate increases and Cumulative Steam Oil Ratio (CSOR) declines with time. This theory is tested via comparison with several field data sets to show the adequacy of the model.

Fibre optic seismic sensor for down-well monitoring in the oil industry

Steam-assisted gravity drainage (SAGD) technology is highly promising for heavy oil and extra heavy oil reservoirs exploitation. Proper monitoring of the SAGD process is essential to improve production efficiency and avoid operational issues. Among all the monitoring techniques, seismic monitoring can provide useful information about the steam-chamber development. In this paper, we demonstrate a seismic monitoring system based on dual-pulse heterodyne demodulation technique, of which the structure is very simple and easy to be installed into downhole. Field trials have been conducted in Xinjiang Oilfield, China. The results validate the performance of the system and indicate its applicability in SAGD process monitoring.

Role of Minerals in Hydrogen Sulfide Generation during Steam-Assisted Recovery of Heavy Oil

Heavy oil is recovered from reservoirs using steam-assisted technology, which can lead to H2S generation if the oil is relatively sulfur-rich. We have used laboratory aquathermolysis to simulate the steam-assisted gravity drainage process and have compared free heavy oil to that contained within the mineral matrix. The presence of a mineral matrix was found to affect the amount of H2S produced and the chemical properties of the oil generated. Our findings show that H2S production is initiated by the presence of naturally occurring minerals at specific temperatures and pressures and production techniques that avoid these conditions will minimize H2S production.

Investigation of initial water mobility on steam-assisted gravity drainage performance using a two-dimensional physical model

Steam-assisted gravity drainage (SAGD) has become a primary commercial in-situ recovery method for oil sands in Alberta, Canada. Industrial field studies have found that the initial water mobility in oil sands has an impact on the SAGD process. However, no experimental research has been conducted to investigate such effects on SAGD performance. In this study, a novel two-dimensional (2-D) physical model with a water-flow boundary is designed for the first time to simulate the flow of initial water in oil sands during the SAGD process. The model investigates the impact of initial water mobility on the steam chamber shape and captures the growth of the steam chamber at different times. The experimental results show that low initial water mobility can promote vertical and lateral growth of the steam chamber, compared to immobile initial water, while high initial water mobility results in accelerated vertical expansion of the steam chamber in the SAGD process. The oil recovery in the scenario of low initial water mobility is 6.6% higher than that of immobile initial water scenario, and is 12.6% higher than that of high initial water mobility scenario. Subsequently, the numerical simulation study for the experiments is conducted in order to acquire insight into the effects of initial water mobility on SAGD performance. Results show that initial water mobility has a great influence on water movement profiles and water distribution along the steam chamber boundary in the SAGD process.

Evolution characteristics of SAGD steam chamber and its impacts on heavy oil production and heat consumption

Currently, Steam-Assisted Gravity Drainage (SAGD) is the most successful commercialized method used to produce bitumen from oil sands and heavy oil reservoirs. Precise description of the steam chamber evolution is important for evaluating the economic effectiveness and Greenhouse Gas (GHG) emission of the SAGD process. In this study, the properties of MacKay River Oil Sands were used in laboratory experiments to compare the chamber evolution and production performance of SAGD under different permeability distributions. Then, a mathematical model was established to predict the steam chamber evolution and the closely related oil production and heat consumption in a heterogeneous formation. Next, the calculated production performance and steam chamber evolution were compared with measured experimental data to verify the accuracy of the model. Finally, the chamber evolution characteristics and their impacts on SAGD oil production and heat consumption are discussed in this paper for formations with different permeability distributions. The results indicate that horizontal permeability controls the evolution of steam chamber such that higher horizontal permeability may cause an obvious convex shape of the chamber edge, whereas vertical permeability has little effect on the chamber shape despite significant influence on the oil production in the early stage of SAGD. Moreover, a convex-shaped chamber interface indicates a higher production rate in the spreading stage and a lower rate in the depleting stage. In addition, this study shows that to minimize the heat consumption of the SAGD process, so that GHG emission can be curbed, a concave-like chamber shape is favorable in the early spreading stage, whereas a convex shape is better in the late spreading stage and depleting stage.

Stacking Approach for Soft Sensor Design in Steam Assisted Gravity Drainage Applications

This paper proposes a stacking soft sensor approach for the oil sands process, known as Steam Assisted Gravity Drainage (SAGD), which is an advanced underground bitumen extraction process. It involves developing multiple predictive models at the base level, followed by correcting the predictions using a higher level synthetic model. Multiple linear regression is utilized as the higher level model. Two case studies, Annual Reservoir Pressure soft sensor and Water Content soft sensor, are presented to demonstrate the feasibility and effectiveness of the proposed stacking approach for soft sensor design in SAGD process.

Impact of geomechanical effects during SAGD process in a meander belt

In the reservoir simulations, the geomechanical effects are usually taken into account to describe the porosity and the permeability variations. In this paper, we present a new method, patented by authors, which allows to model the geomechanical effects also on the well productivity index. The Steam Assisted Gravity Drainage (SAGD) method is widely used for the heavy oil production. A very high variation in pressure and temperature play a significant role on the petrophysical properties and may impact the productivity estimation. In this paper we develop a new simplified geomechanical model in order to account for the thermal and pressure effects on the porosity, permeability and the productivity index during the reservoir simulation. At the current state, these dependencies are defined using semi-analytical relationships. The model is applied to a meandering fluvial reservoir based on 3D outcrop observations. The productivity is found underestimated if the pressure and temperature effects on the petrophysical properties are ignored in the reservoir simulation. Moreover, this study shows an important impact of thermal effects on the productivity estimation. The results of this work show that it is essential to properly take into account the geomechanical effects on the petrophysical properties and also on the productivity index for a better productivity estimation.

Study of oil filtration in porous media under the steam-assisted gravity drainage process

This work is devoted to the development and computer realization of a three-dimensional mathematical model describing the processes of flow, filtration and phase transition during the hot steam injection into a rock mass. The specific feature of the developed model is the possibility to take into account the dependence of thermophysical properties of each component in a multicomponent flow on time or spatial coordinates. It is assumed that considered media is a multicomponent system consisting of steam, oil and water filling the pore space. The developed model includes mass balance equation for components characterizing water and steam saturations, the condition of a fully saturated media to define the oil component of the flow, Darcy’s law for the filtration flow of the multicomponent stream and the law of conservation of energy taking into account the convective heat transfer and the source describing the «steam-water» phase transition. Computer realization of the proposed model is based on the transformation of the system of equations in such a way that the values of steam and water saturations as well as pressure act as unknown variables; representation of the resulting system of equations in a weak form and the introduction of additional stabilization terms. The adequacy of the proposed model and the efficiency of the developed approach to its implementation are illustrated by a three-dimensional numerical simulation of oil production process through the steam-assisted gravity drainage method in the oil sand.

Experimental study and numerical simulation of nitrogen-assisted SAGD in developing heavy oil reservoirs

The presence of significant amounts of injected steam and heat loss are unavoidable issues occurred that are observed during the steam-assisted gravity drainage (SAGD) process in developing heavy oil reservoirs. Because of these limitations and concerns, non-condensable gas co-injection has become a potential technique to enhancing oil recovery and reducing energy consumption. However, the oil production mechanism is complicated and has not been totally understood, thereby requiring further discussion. In this work, a two-dimensional physical model was designed to investigate the production mechanisms of nitrogen on SAGD. Two comparative injection schemes, specifically the conventional SAGD and nitrogen assisted SAGD (NA-SAGD), were conducted to investigate the effect of nitrogen co-injection with steam on the SAGD performance. Dynamic temperature profile changes during the two experiment processes were monitored and recorded. The observation results indicate that nitrogen accumulation at the upper part of the model resulted in the effective expansion of the NA-SAGD process steam chamber along the horizontal direction. The swept area of steam increased significantly and the residual oil saturation was reduced. The cumulative oil production of NA-SAGD was higher than that of the conventional SAGD. Moreover, the apparent heat loss reduction, which defines the heat utilization efficiency, exhibited an increase following nitrogen injection. In addition, a numerical simulation was generated to compare and verify the results obtained in the two experiments. Nitrogen co-injection with steam effectively enhanced the oil recovery. Studies indicate that NA-SAGD is a feasible method for improving oil production in developing heavy oil reservoirs.

Numerical Simulation Study on Steam-Assisted Gravity Drainage Performance in a Heavy Oil Reservoir with a Bottom Water Zone

In the Pikes Peak oil field near Lloydminster, Canada, a significant amount of heavy oil reserves is located in reservoirs with a bottom water zone. The properties of the bottom water zone and the operation parameters significantly affect oil production performance via the steam-assisted gravity drainage (SAGD) process. Thus, in order to develop this type of heavy oil resource, a full understanding of the effects of these properties is necessary. In this study, the numerical simulation approach was applied to study the effects of properties in the bottom water zone in the SAGD process, such as the initial gas oil ratio, the thickness of the reservoir, and oil saturation of the bottom water zone. In addition, some operation parameters were studied including the injection pressure, the SAGD well pair location, and five different well patterns: (1) two corner wells, (2) triple wells, (3) downhole water sink well, (4) vertical injectors with a horizontal producer, and (5) fishbone well. The numerical simulation results suggest that the properties of the bottom water zone affect production performance extremely. First, both positive and negative effects were observed when solution gas exists in the heavy oil. Second, a logarithmical relationship was investigated between the bottom water production ratio and the thickness of the bottom water zone. Third, a non-linear relation was obtained between the oil recovery factor and oil saturation in the bottom water zone, and a peak oil recovery was achieved at the oil saturation rate of 30% in the bottom water zone. Furthermore, the operation parameters affected the heavy oil production performance. Comparison of the well patterns showed that the two corner wells and the triple wells patterns obtained the highest oil recovery factors of 74.71% and 77.19%, respectively, which are almost twice the oil recovery factors gained in the conventional SAGD process (47.84%). This indicates that the optimized SAGD process with the two corner wells and the triple wells pattern is able to improve SAGD production performance in a heavy oil reservoir with a bottom water zone.

Experimental and numerical study of the convective mass transfer of solvent in the Expanding-Solvent SAGD process

In the Expanding-Solvent Steam-Assisted Gravity Drainage (ES-SAGD) process, the mass transfer of the dissolved solvent in the steam chamber boundary is critical to the oil production performance. In this study, experimental and numerical simulation approaches are used to investigate the gravity-driven convective movement of solvent in the steam chamber boundary in ES-SAGD. The experiments are conducted in a two-dimensional (2-D) sandpack model, in which a sloping gas-liquid interface in a closed system is developed as an analog of the steam chamber boundary in ES-SAGD. Thus, the flow along the sloping gas-liquid interface is used to represent the flow in the steam chamber boundary in ES-SAGD. Solvent mass transfer is observed by its concentration variation in the direction perpendicular to the flow surface. Later, CMG STARS is used as the simulator to execute the numerical simulations, and the simulation successfully captured the experimental results. In this study, the findings demonstrate the existence of convective solvent movement along the sloping gas-liquid interface. Furthermore, the results show that there is accelerated solvent movement along the interface under high permeability, and slow movement along the interface under high flow rate and high fluid viscosity. Diffusion and dispersion are tested by varying the corresponding coefficients in the physical and numerical models, and results show that these phenomena have negligible effect on the transverse solvent mass transfer process. This study found that gravity-driven convection is the dominant mechanism of solvent mass transfer in the steam chamber boundary in ES-SAGD.

Feasibility study on application of the recent enhanced heavy oil recovery methods (VAPEX, SAGD, CAGD and THAI) in an Iranian heavy oil reservoir

ABSTRACTEnhanced oil recovery (EOR) methods assisted by gravity drainage mechanism and application of sophisticated horizontal wells bring new hope for heavy oil extraction. Variety of thermal and non-thermal EOR techniques inject an external source of energy and materials such as steam, solvent vapor, or gas through a horizontal well at the top of the reservoir to reduce in-situ heavy oil viscosity. So, the diluted oil becomes mobile and flows downwards by gravity drainage to a horizontal producer located at the bottom of the reservoir.In this paper, a sector model of an Iranian fractured carbonate heavy oil reservoir was provided to simulate and evaluate capability of some EOR techniques such as Vapor Extraction (VAPEX), Steam Assisted Gravity Drainage (SAGD), Combustion Assisted Gravity Drainage (CAGD), and Toe to Heel Air Injection (THAI) at its reservoir conditions and fluid properties. The simulation results demonstrated that wet CAGD in comparison with other nominated methods could improve heavy oil recovery factor to around 19% much more than each of SAGD, THAI, and VAPEX techniques. It could also reduce the total energy to produced oil ratio index up to 82% with respect to SAGD process in a year.Although lower oil recovery has been gained by VAPEX process, but using a proper vaporized solvent could produce a kind of de-asphalted and upgraded oil with increased API gravity up to 29°API with no considerable solvent loss.

Design of flow control devices in steam-assisted gravity drainage (SAGD) completion

Commercialization of the steam-assisted gravity drainage (SAGD) process has made recovery of heavy oil/bitumen possible in a number of reservoirs hindered by hydrocarbon immobility. However, the economics of this process are highly sensitive to the efficiency of steam creation, delivery, and use, with a successful and unsuccessful SAGD well pair often separated by how effectively thermal inefficiencies can be mitigated in the flow profiles of steam injection and/or in emulsion recovery. To improve flow profiles, Albertan SAGD completions have experimented with the addition of flow control devices (FCDs). These completion tools have historically been used to regulate liquid inflow across long producing laterals, adding a variable pressure drop along the lateral to improve the conformance of hydrocarbon production and delay water breakthrough; within SAGD completions, FCDs find novel use to force a more even flow distribution of steam in the injector and a thermally dependent inflow profile in the producer to maximize recovery of heavy oil/bitumen. This paper provides a comprehensive overview of different FCD designs, discussing their respective methods of regulation, the fluid-adaptive behavior of “autonomous” FCDs, operational strengths and weaknesses of different commercial offerings, and suggestions on how to use existing pressure loss models for FCDs and apply them to the non-traditional application of regulating SAGD flow profiles, both for equipment sizing and estimation of pressure loss/flow rates across the device. From this work, it is proposed that use of autonomous FCDs in the production lateral are of greater value than use of flow control in the injector; however maximum benefits are achieved by coupling simple orifice-style FCDs in the injector lateral with autonomous, large flow path (non-orifice) FCDs capable of controlling steam flash events in the production well.

Enhanced oil recovery and natural bitumen production through the use of sinusoidal wells and solar thermal method

Thermal enhanced oil recovery is known to be the most effective way of heavy oil production. This article discusses the application of sinusoidal wells to improve the efficiency of thermal enhanced oil recovery methods. As a result of numerical simulation of steam-assisted gravity drainage (SAGD) process, it has been shown that the application of sinusoidal wells allowed 8990 m3 of the incremental oil production during 10 years simulation period. However, the high cost of hot water and steam generation, as well as significant environmental impact, limit the application of thermal oil recovery methods. The article presents the concept of year-round generation of desalinated hot water and steam from sea and reservoir brine at low cost by the newly developed solar collector. The collector can be placed in the vicinity of injection wells to provide constant hot water, steam, and electrical power supply.

Novel insights on the impact of top water on Steam-Assisted Gravity Drainage in a point bar reservoir

Summary As efforts are made to efficiently exploit and recover bitumen resources in Canada, increasingly more complex reservoirs in the Athabasca area continue to challenge the application of Steam-Assisted Gravity Drainage (SAGD) technology. Several studies have been done to investigate the impact of heterogeneities/complexities such as shale barriers, lean zones, and top and bottom water on the performance of the SAGD process. However, the literature is deficient for point bar deposits with top water zones, a common occurrence in oil sands systems. This study, by using thermal reservoir simulation, examines SAGD performance in a point bar deposit reservoir where an overlying top water and an inclined heterolithic strata (IHS) is present. The results show that where the top water is unconfined and steam injection pressure is higher than that of the top water zone, there is a loss of thermal energy, but the top water does not impact steam chamber development. At steam injection pressure lower than that of the top water zone, top water continuously drains into the reservoir and constrains the size of the chamber. However, the IHS zone helps to delay drainage of the top water into the chamber when steam is injected at underbalanced conditions. Finally, under proper steam injection pressure conditions, top water production can be considerably delayed.