Steam Assisted Gravity Drainage Operations Research Articles

A kelly criterion based optimal scheduling of a microgrid on a steam-assisted gravity drainage (SAGD) facility

Steam Assisted Gravity Drainage (SAGD) is one of the major thermal recovery techniques to extract the Canadian bitumen. In the process, there is substantial amount of heat left behind in the reservoir at the end of SAGD operations, which can be converted to electricity and distributed profitably utilizing a microgrid. Concurrently, based on Canada’s green energy initiative, we present the integration and optimal power management of a microgrid on a SAGD facility, comprising of an Organic Rankine Cycle based turbine (ORC), a Gas Turbine (GT), a Battery Storage System (BSS), the central grid and the SAGD facility as the load. We introduce a Kelly Criterion (KC) based microgrid scheduling technique, which is based on maximizing information gain and is independent of supply-demand relationships. Based on the formulation, it was hypothesized that the KC based algorithm is superior compared to standard optimization techniques in a highly volatile electricity market. The electricity market volatility is captured via a wavelet network based forecasting technique. The case study presented highlights the advantages of the KC approach and its efficacy in a highly volatile energy market. The results show the superiority of the KC based scheduling algorithm in highly volatile energy markets, with forecast data irregularities.

Geomechanical Characterization of Inclined Heterolithic Stratification Lithosome and Its Permeability Evolution under SAGD Stress Paths

Summary A sizeable portion of the Athabasca oil sand reservoir is classified as inclined heterolithic stratification lithosomes (IHSs). However, due to the significant heterogeneity of IHSs and the minimal experimental studies on them, their hydrogeomechanical properties are relatively unknown. The main objectives of this study are investigating the geomechanical constitutive behavior of IHSs and linking their geological and mechanical characteristics to their hydraulic behavior to estimate the permeability evolution of IHSs during a steam-assisted gravity drainage (SAGD) operation. To that end, a detailed methodology for reconstitution of analog IHS specimens was developed, and a microscopic comparative study was conducted between analog and in-situ IHS samples. The SAGD-induced stress paths were experimentally simulated by running isotropic cyclic consolidation and drained triaxial shearing tests on analog IHSs. Both series of experiments were performed in conjunction with permeability tests at different strain levels, flow rates, and stress states. Additionally, an analog sample with bioturbation was tested to examine the hydrogeomechanical effects of bioturbation. Finally, the hydromechanical characteristics of analog IHS were compared with its constituent layers (sand and mud). The microscopic study showed that the layers’ integration and grain size distributions are similar in analog and in-situ IHS specimens. The results also revealed that geomechanical properties of IHSs, such as shear strength, bulk compressibility, Young's modulus, and dilation angle, are stress-state dependent. In other words, elevating the confining pressure could significantly increase the strength and elastic modulus of a sample, while decreasing the compressibility and dilation angle. In contrast, the friction angle and Poisson's ratio are not very sensitive to changes in the isotropic confining stress. An important finding of this study is that the effect of an IHS sample's volume change on permeability is contingent on the stress state and stress path. Volume change during isotropic unloading-reloading resulted in permeability increases, and sample dilation during compression shearing resulted in permeability decreases, especially at high effective confining stresses. Moreover, the tests revealed that the existence of bioturbation dramatically improves permeability of IHSs in comparison to equivalent nonbioturbated specimens but has negligible effects on its mechanical properties, which remain similar to nonbioturbated specimens. The results also showed that bioturbation had minimal impact on permeability changes during shearing. Lastly, experimental correlations were developed for each of the preceding parameters mentioned. For the first time, specialized experimental protocols have been developed that guide the infrastructure and processes required to reconstitute analog IHS specimens and conduct geomechanical testing on them. This study also delivered fundamental constitutive data to better understand the geomechanical behavior of IHS reservoir and its permeability evolution during the in-situ recovery processes. Such data can be used to accurately capture the reservoir behavior and increase the efficiency of SAGD operations in IHS reservoirs.

Predicting Geomechanical Dynamics of Steam-Assisted Gravity-Drainage Process. Part II: Modified Cam-Clay Model

SummaryIn Part I of this study (Irani 2018), the geomechanical effects in the reservoir associated with steam-assisted gravity drainage (SAGD) steam chamber growth was evaluated on the basis of two core assumptions: reservoir yield behavior follows that of the Mohr-Coulomb (MC) dilative behavior, and the reservoir stress response follows that of a drained sand. In Part I, it was shown that although the dilative model nicely described the shearing and the sheared zone thickness at the front of the SAGD steam chamber, it could not predict the displacements associated with cold dilation in SAGD reservoirs, in which cold dilation refers to vertical displacement created in the zone ahead of the heated zone caused by isotropic unloading generated by the pore pressure increase and the increase in far-field horizontal stress. In cold dilation, the stresses do not reach the critical state line (CSL), which defines the yield surface and should, therefore, be analyzed considering elastic behavior. A modified Cam-Clay (MCC) model, however, can be used to describe the behavior of the oil sand in the cold dilation zone before reaching the CSL. In this study and as an extension to the results presented in Part I, strains developed in the reservoir during SAGD operation are calculated using an MCC model, and the associated oil rate enhancement and displacements are evaluated. The vertical strains and displacements are compared with measured values from the extensive monitoring program conducted at the Underground Test Facility (UTF) in the late 1980s. Two aspects of geomechanical effects are compared between the cap models (Part II) and dilative models (Part I): first, prediction of the sheared zone thickness and its effect on SAGD production enhancement, and second, prediction of vertical and horizontal displacements. It is shown that consideration of the material model effects on production rates are negligible for both models and that the MCC model can predict displacements in both the heated and cold zones of the reservoir reasonably accurately. Although dilative constitutive models can be used to predict horizontal and vertical displacements in the heated zone quite accurately, they lack the ability to predict the response in the “cold dilation zone.” Another main advantage of using an MCC model is that the MCC model provides a better description of a stress path and how the reservoir mobility can affect reservoir dilation, especially in the cold dilation zone.

Understanding the effect of skim oil recycle on the water/oil separation in steam assisted gravity drainage operations

In steam assisted gravity drainage (SAGD) operations, skim oil recycled to a free water knockout (FWKO) often results in poor water quality and rag formation at the oil/water interface. To improve water quality and demulsification efficiency in the presence of skim oil recycle, it is necessary to understand the status of oil and solids in the produced water throughout the process. In this paper, the effect of skim oil on the water/oil separation in SAGD operations was studied. Dynamic optical fluid imaging (DOFI) technology was used to characterize oil and solids concentrations, oil droplet sizes, and the associated size distributions in the produced water collected from various vessels in a SAGD process. The DOFI analyses show that skim oil recycle caused more oil and solids to be sent to the FWKO, treater and induced gas flotation (IGF) outlet waters and finally to oil removal filters (ORF). The increased oil in water led to more oil droplets, especially more numerous small oil droplets remaining in the produced water. These small oil droplets are more challenging to remove than larger oil droplets, resulting in deteriorated water quality. Skim oil recycle decreased the oil removal efficiency of the IGF vessel and increased fouling of ORF filters by oil and solids. Fourier transform infrared spectroscopy analysis of the solids collected from the produced water in the presence of skim oil recycle indicated that the solids are bitumen-coated fine quartz and clays. Demulsification studies show that application of dual reverse emulsion breakers could help improve water quality and alleviate the negative effects due to the solids from skim oil addition.

Technology Focus: Heavy Oil (April 2020)

Technology Focus Reviewing a myriad of papers presented at different conferences during the past year and attending some of those to hear the oral presentation versions, I can group the current trends in heavy-oil operations and research into two major categories: Process optimization and use of chemicals as additives to steam and water. Here are some highlights from those categories. Several papers focused on purely computational methods—including multi-objective optimization and proxy models—to optimize the steam-assisted gravity drainage (SAGD) method with specific attention on preferential steam allocation. Real-life examples of these applications consist of inflow- and outflow-control devices and steam splitters developed for diverting the steam to preferential zones, thus minimizing the use of steam. As an indirect meth-od to provide supplemental data for the optimized solutions, seismic data were also used. Applications of seismic waves include the depiction of steam-chamber development and monitoring wellbore integrity. Considering that many SAGD operations are reaching maturity, these applications will help maintain the steam/oil ratios at low levels, therefore extending the life of the processes. In another group of studies, chemical additives were tested at the laboratory scale to improve cold (microemulsion formulations) and thermal (to reduce steam/oil ratio) heavy-oil recovery. Examples of newly trialed chemicals include ionic liquids, foam additives, anionic and hydrophobic surfactants, switchable-hydrophilicity tertiary amines, nano-fluids (dispersed SiO2 and ZrO2), ethers, alcohols, and chelating agents as steam additives and microemulsion formulations using SiO2, anionic and nonionic surfactants as well as deep eutectic solvents for cold production. Although most of the listed optimization studies (specific examples reported include the Mackay River, Firebag, and Surmont fields) and chemical tests were done for SAGD conditions (especially at the mature level), these new technologies and applications will be a guidance to the other types of steam operations (cyclic steam injection and steamflooding) using horizontal injectors and producers. In addition to the discussed studies and practices, a plethora of field-scale activities from the Middle East, far east Asia, and the Americas have been reported on consistently. Most of those are early-stage practices or pilots, but a few are related to mature heavy-oil recovery operations. Examples include Kuwait (data collection and development plans for new heavy-oil potentials), Oman (steam management surveillance in the Mukhaizna field), Brazil (development options for the offshore Atalanta field), Venezuela (ongoing operations in the Orinoco belt), Alaska (field-scale polymer-flooding test), China (practices in the Liaohe and Bohai Bay fields), Canada (cold production using methane/ propane mixture and electrical heating pilots in Alberta), Colombia (applications of autonomous inflow-control devices in the Rubiales field), and Indonesia (identification of rod-pump failures in the Duri field). Recommended additional reading at OnePetro: www.onepetro.org. SPE 196072 Laboratory and Field Testing of a Steam-Limiting Flow-Control Device Developed for Thermal Applications by Marty Lastiwka, Suncor Energy, et al. SPE 197321 Surveillance Approach of Steam Management in a Heavy-Oil Reservoir, Oman by Hajer Al Mahruqi, Occidental Petroleum SPE 198697 Effective Reservoir Management With Flow-Control Devices for SAGD Producer Wells in the Mackay River by Giuseppe Rosi, RGL Reservoir Management, et al.

Analysis of Athabasca Oil Sands Investigates SAGD Performance Variability

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 195348, “Steam-Assisted Gravity Drainage Performance Variability—Analysis of Actual Production Data for 28 Athabasca Oil Sands Well Pairs,” by Quang T. Doan, Vincano; S.M. Farouq Ali, SPE, University of Houston; and Thomas B. Tan, SPE, Petrostudies Consultants, prepared for the 2019 SPE Western Regional Meeting, San Jose, California, 23–26 April. The paper has not been peer reviewed. Steam-assisted gravity drainage (SAGD) performance in bitumen-recovery projects in Alberta is affected by geological deposits, reservoir quality, and operational experience. The authors reviewed and analyzed actual field production and injection data for 28 Athabasca oil-sands-deposit SAGD well pairs (WPs). Based on analysis of field-production data, a numerical model was built and calibrated against production data from two of the poorer-performing WPs among the 28 studied. Agreement between simulated and actual cumulative oil and steam/oil ratio (SOR) was within 10% after 6 years of operations on a first-iteration basis. Problem and Investigation Methodology A survey of the literature reveals that some aspects of the SAGD process, particularly with regard to the behavior of gas, still largely are not understood. While successful history-matching simulations of SAGD WPs exist for several different projects, these rely on dead-oil pressure/volume/temperature treatment and exclude any findings and discussion on gas production. Such history-matched models likely would need to be modified significantly to be useful for modeling the wind-down stage of SAGD operations. Recent numerical studies modeling the generation of aquathermolysis gases focused on the injection of noncondensable gas into a mature SAGD steam chamber. In preparation for a series of numerical studies on aspects of SAGD performance, a reservoir model simple enough to be relatively adaptable for different geological settings was built. Such a model had to be calibrated rigorously with actual production data to provide a high degree of confidence in its results and predictive capability in appropriate contexts. The investigation in the complete paper is aimed at addressing several fundamental aspects of SAGD operations, including the effects of reservoir heterogeneities and the behavior of gas. The first part of the complete paper is focused on reviewing and analyzing actual field production data spanning more than 1,700 days from 28 SAGD WPs from four different pads (A, B, C, and D) of the Jackfish 1 project; this synopsis will not include that extensive data. Jackfish 1 Project. Jackfish 1 consists of 42 WPs divided into six pads (including the 28 WPs in Pads A, B, C, and D analyzed for the authors’ study) and is part of the geological oil-sands trend of the Athabasca oil-sands deposit. Jackfish 1 has a nameplate capacity of 35,000 BOPD, with a designed SOR of 2.7. Consistently exceeding 90% of its nameplate capacity since first steam, it is commonly considered to be a successful SAGD project. The results of data analysis for the WPs studied indicated the following: Considerable variance exists in the recovery performance of SAGD WPs on the same pad. Considering the small drainage area of the 7-WP pad (800×800 m), such variances bear important implications for the planning and execution of SAGD projects (particularly greenfield development but also with regard to brownfield expansion). The authors stress that forecasting project productivity should not be based on a single-WP, deterministic simulation model without any consideration for distributions in reservoir geology and parameters affecting SAGD performance. This assessment is equally applicable in the estimation of reserves.

Effect of Slot Width and Density on Slotted Liner Performance in SAGD Operations

Sand production from a poorly consolidated reservoir could give rise to some severe problems during production. Holding the load bearing solids in place is the main goal of any sand control technique. The only sand control techniques that have found applications in steam assisted gravity drainage (SAGD) are some of the mechanical methods, including wire wrapped screens, slotted liners and more recently, punched screens. Slotted liner is one of the most effective mechanical sand control methods in the unconsolidated reservoir exploitation, which has proven to be the preferred sand control method in the SAGD operations. The main advantage of the slotted liners that makes them suitable for SAGD operations is their superior mechanical integrity for the completion of long horizontal wells. This study is an attempt to increase the existing understanding of the fines migration, sand production, and plugging tendency for slotted liners by using a novel large-scale scaled completion test (SCT) facility. A triaxial cell assembly was used to load sand-packs with specified and controlled grain size distribution, shape and mineralogy, on multi-slot sand control coupons. Different stress levels were applied parallel and perpendicular to different combinations of slot width and density in multi-slot coupons, while brine was injected from the top of the sand-pack towards the coupon. At each stress level, the mass of produced sand was measured, and the pressure drops along the sand-pack and coupon were recorded. Fines migration was also investigated by measuring fines/clay concentration along the sand-pack. The current study employed multi-slot coupons to investigate flow interactions among slots and its effect on the flow performance of liner under typically encountered stresses in SAGD wells. According to the experimental observations, increasing slot width generally reduces the possibility of pore plugging caused by fines migration. However, there is a limit for slot aperture beyond which the plugging is not reduced any further, and only a higher level of sanding occurs. Test measurements also indicated that besides the slot width, the slot density also influences the level of plugging and sand production and must be included in the design criteria.

Graph-based determination of structural controllability and observability for pressure and temperature dynamics during steam-assisted gravity drainage operation

Steam assisted gravity drainage (SAGD), which is used for the in-situ extraction and recovery of oil sands bitumen, is represented by a distributed parameter system (DPS). The problem of sensor placement and the control of steam chamber growth and oil production, respectively, require analysis of the observability and controllability of the system. In this type of system, parametric sensitivity is traditionally used in lieu of observability, and controllability has not been explored rigorously. In this work, we analyze the pressure and temperature fields of a SAGD model based on detailed reservoir simulations and present a data-driven technique to assess the structural controllability and observability of the system, with a view to determine optimal locations of actuators and sensors. An agglomerative hierarchical clustering technique is used to obtain a spanning tree of the clusters which is partitioned based on an objective function to arrive at a set of spatially contiguous clusters that display similar pressure/temperature dynamics. A Granger causality measure is used to create the linkage amongst the clusters to build a digraph model of the data. The driver nodes of the graph identify locations for actuation which provide full control over the graph, and the root strongly connected components indicate sensor locations which ensure structural observability over the entire graph. We demonstrate the method using data generated from SAGD simulations using the CMG-STARS simulator, identify the sensor and actuator locations required for complete structural observability and controllability of the system, and also provide a method of assessment of partial actuation and in-sensor ranges.

Developing a methodology to characterize formation damage (pore plugging) due to fines migration in sand control tests

Stand-alone screens (SAS) have been widely used in steam assisted gravity drainage (SAGD) operations. Although many researchers investigated the flow performance of SAS through sand control tests, the formation damage (pore plugging) due to fines migration has not been characterized under multi-phase flow conditions. In this study, a methodology is developed to quantify and characterize the fines migration under multi-phase flow sand control testing conditions.A large-scale sand retention test (SRT) facility is used to investigate the flow performance of SAS. Duplicated sand samples with similar particle size distribution (PSD), shape, and mineralogy properties to the McMurray Formation oil sands are obtained by mixing different types of commercial sands, silts, and clays. Oil and brine are simultaneously injected into the sand-pack at different water-cut levels and liquid rates to emulate the changing inflow conditions in SAGD operations. The saturation levels in each flow stage are measured to determine the relative permeability values. Next, the relative permeability curves of the duplicated sand-pack sample are measured following the steady-state method. Finally, the pressure data obtained from the SRT in each flow stage are coupled with the relative permeability values to calculate the retained permeability as the indicator of flow performance of SAS'.Generally, testing results show that single-phase oil flow generates minor and negligible permeability impairments in the near-screen zone of the sand-pack. An evident permeability reduction is observed once the water breakthrough happens, indicating that the wetting-phase fluid significantly mobilizes fine particles and causes pore plugging. Also, with the increase of flow rate and water cut, a further reduction in permeability is found as a result of the higher drag force and greater exposure area of fines to brine.The proposed methodology presented in this study allows quantitative characterization of the formation damage under multi-phase flow condition and provides a practical and straightforward method for the evaluation of the SAS's flow performance.

Application of Geochemical and Isotopic Tracers for Characterization of SAGD Waters in the Alberta Oil-Sand Region

Summary Mineral precipitation (scale) can significantly hinder production in petroleum reservoirs. This includes steam-assisted-gravity-drainage (SAGD) operations used for bitumen recovery in the Athabasca oil-sand region (AOSR) of northeastern Alberta, Canada. We explored whether select geochemical and isotope tracers (δ2H, δ18O, δ11B, δ34S, δ13C, 87Sr/86Sr) in SAGD-water sources can help to improve the understanding of the dynamics of reservoir fluids and their mixing in SAGD operations that might contribute toward scale precipitation. Pore water, bottom-formation water, steam condensate, and returned emulsions (produced bitumen and water) were sampled from an SAGD reservoir in northeastern Alberta and analyzed for geochemical and isotopic parameters. The results obtained indicate distinct Na and Cl concentrations and δ18O and δ2H values for these fluid sources. Significant differences in δ13CDIC, δ11B, and δ34S values and 87Sr/86Sr ratios were observed between bottom-formation water, steam condensate, and returned-water samples and hence constitute excellent tracers for bottomwater (BW) influx.

Bayesian Biclustering by dynamics: A clustering algorithm for SAGD time series data

Steam-Assisted Gravity Drainage (SAGD) is an extra heavy oil recovery process consisting of an upper horizontal steam injector and a lower horizontal producer that removes fluids from the reservoir. Given its costs and environmental impact, SAGD injection strategies must be examined to find ways to improve performance. In this paper, a new Bayesian Biclustering by Dynamics (BBCD) method is proposed, which finds and differentiates groups of SAGD wells based on their oil production response to steam injected over time. This is a greedy algorithm that automatically clusters both rows and columns of SAGD injection and production data and then generates a descriptive summary for each cluster. Clusters are described with probability distributions that capture the likelihood of transitioning between discrete steam-to-oil ratio states. In addition, BBCD incorporates background knowledge on SAGD directly into the clustering process via prior transition probability distributions. Real SAGD operation data from sites in Alberta, Canada are used for this analysis. The results reveal nine production responses to two different steam injection strategies, and new insights into SAGD process performance.

Integration of data-driven modeling techniques for lean zone and shale barrier characterization in SAGD reservoirs

High water saturation zone, which is also known as lean zone, and shale barrier, are two common types of heterogeneous features in steam-assisted gravity drainage (SAGD) reservoirs. Lean zone poses a detrimental influence on conventional SAGD operations, as it causes steam utilization efficiency to decrease and increases the steam-oil ratio. Shale barrier would also impede the vertical growth and lateral spread of a steam chamber and potentially reduce oil production. An efficient characterization workflow is proposed to estimate the quantity, location, and volume of these heterogeneous features by integration of data-driven modeling techniques.Field data including geophysical, operational and production data corresponding to several existing SAGD projects are extracted from the public domain and used to build a series synthetic homogeneous models. Lean zones and shale barriers with varying distribution and volume are randomly added. From the corresponding production time-series data, a set of input features are identified through a hybrid method comprised of discrete wavelet transformation (DWT) and principal component analysis (PCA), while the output parameters are formulated to describe the actual number and geological parameters of two types of reservoir heterogeneities. A two-level data-driven model based on artificial neural networks (ANN) is employed to correlate the complex relationship between input and output attributes. Finally, this calibrated model is integrated into a novel characterization workflow to infer an ensemble of probable realizations of lean zone and shale barrier distribution that are conditioned to a given production historical profile.This work demonstrates the potential of practical application of data-driven models in correlating complex reservoir heterogeneity properties and production time-series data. Results from the case study illustrate the utility of the proposed workflow in facilitating the efficient identification of heterogeneous features from SAGD profiles. The potential savings of computational efforts associated with the proposed methodology are also explained.

Proxy models for caprock pressure and temperature dynamics during steam-assisted gravity drainage process

The usage of first principles-based dynamic models for advanced control, monitoring and optimization of petroleum reservoirs is constrained by the large scale nature of the models. The parametric uncertainty makes the process even more challenging; hence, development of proxy models is an attractive proposition. In this work, proxy models are developed from spatio-temporal data of pressure and temperature in the caprock during steam-assisted gravity drainage operation. The first proxy model addresses the issue of reduced-order dynamic modelling of the caprock pressure and temperature fields based on proper orthogonal decomposition and system identification using data from the first principles model. The second proxy model takes the first step towards dynamic analysis of factor of safety in reservoir management by modelling the evolution of clusters of high, medium and low pressure regions using graph theory and subspace modelling. System theoretic properties of these proxy models and their practical relevance is also analysed.

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.

Optimal scenario design of steam-assisted gravity drainage to enhance oil recovery with temperature and rate control

Steam-assisted gravity drainage (SAGD) is a commonly used thermal enhanced oil recovery (EOR) method in heavy oil reservoirs. Scenario optimizations are conducted with different optimization techniques to determine the optimal steam injection rate and temperature strategies. The performance of standard artificial bee colony (SABC), directed ABC (DABC), generalized pattern search (GPS) and mesh-adaptive direct search (MADS) algorithms were investigated. Also, the effect of initial guess and polling type on the performance of GPS and MADS were analyzed. DABC approaches the global optimum better than other employed algorithms, with a huge number of function evaluations. While, GPS is the fastest algorithm, likely to be trapped in local extrema. To eliminate this issue, the novel multi-region pattern search (MRPS) algorithm is proposed, in which the search space is divided into smaller subregions, each one is searched independently. Hence, search space is more efficiently explored and initial guess dependency is reduced. MRPS algorithm provided similar results to the DABC algorithm while lowering the computational costs up to 93%. MRPS algorithm is successfully applied for a 5-year SAGD scenario optimization. Furthermore, by scenario optimization, SAGD operation could be reduced for 1-year, providing the same NPV as that of the reference case operating for 4-years.

Dynamic Steam-Trap-Control Simulation Technique: Formulation, Implementation, and Performance Analysis

Summary Steam-trap subcool is a technique that is used to maintain the energy efficiency of the steam-assisted-gravity-drainage (SAGD) process by most heavy-oil producers in Canada. The concept is rather simple (i.e., create a liquid pool around the production well to prevent steam from escaping from the steam chamber into the production well). A numerical steam trap based on a thermodynamic approach was implemented by Edmunds (2000), and it has been used in simulations with different types of wellbore models in commercial codes. In this approach, a thermodynamic relationship is solved as a well-residual equation to guarantee that the bottomhole temperature (BHT) is less than the saturation temperature of water at the hottest location along the wellbore. The location of the hottest spot along the wellbore is static in time. Steam trap is a dynamic process, and inflow temperatures can vary significantly along the wellbore according to the local fluid and rock properties along the well. It is highly possible that the location of the hottest spot along the well changes frequently with time during the SAGD operation. In this study, the simulation of a dynamic steam-trap-control technique is provided. The location of the hottest spot along the wellbore is scanned at every timestep. Severe numerical instabilities are observed when the thermodynamic approach is used. A new constraint based on the total production rate at reservoir condition is introduced. Details of the mathematical formulation and the numerical behavior of the new method are discussed in this paper. Several real field models with different wellbore designs (multiple tubing strings) are simulated, and the results of the new approach are compared with the thermodynamic approach. Simulation results show that the numerical performance of this new approach is significantly more stable. We also compared the run time of simulation between cases with new well constraint and thermodynamic steam-trap control, and results show a significant improvement in simulation run time.

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.

Data analytics for oil sands subcool prediction — a comparative study of machine learning algorithms

Steam Assisted Gravity Drainage (SAGD) is an efficient and widely used technology to extract heavy oil from a reservoir. The accurate prediction of subcool plays a critical role in determining the economic performance of SAGD operations since it influences oil production and operational safety. This work focuses on developing a subcool model based on industrial datasets using deep learning and several other widely-used machine learning methods. Furthermore, this work compares and discusses the out-of-sample performance of different machine learning algorithms using industrial datasets. In addition, we also show that care has to be taken when using machine learning algorithms to solve engineering problems. Data quality and a priori process knowledge play a role in their performance.

The relationship of liquid level and subcool between injector and producer during SAGD process

Recently, steam assisted gravity drainage (SAGD) has been widely adopted in thermal recovery for heavy oil. However, challenges remain in SAGD development: the close distance between injector and producer makes it easy to cause steam breakthrough, which means lower thermal efficiency as well as higher investment. It is generally acknowledged that there is a liquid level existing between the injector and producer, a reasonable liquid level could prevent steam from being produced directly. The existence of liquid level generates a temperature difference between two wells, i.e., subcool. Subcool has generally been used to describe liquid level in practice and in many researches, yet it is inaccurate. In order to characterize the liquid level precisely, it is necessary to fully clarify the relationship among subcool, liquid level and pressure difference between injector and producer.By analyzing the features of subcool and pressure difference shown in SAGD experiments, it is found that the value of subcool may be not directly relevant with the distance between injector and producer, considering the huge difference between experiments and the measured data from actual oilfield. Correspondingly, liquid level is supposed to be treated as a dimensionless variable, to be specific, named as dimensionless liquid level, defined as liquid level divided by the distance between two wells. Afterwards, over 40 cases of CMG numerical simulations are run to investigate the liquid levels with different injector-producer distances and different subcools. Based on the analysis of simulation results, the dimensionless liquid level increases with subcool, while for a given subcool, dimensionless liquid level is inversely proportional to pressure difference between injector and producer. Accordingly, liquid level could be accurately controlled under a given subcool and pressure gradient, which is applicable and be of great significance for the SAGD operation on the field.

Optimal design of distributed effluent treatment systems in steam assisted gravity drainage oil sands operations

The oil sands industry in Canada is under increasing pressure to simultaneously reduce greenhouse gas (GHG) emissions and water consumption. As a consequence, new trade-offs are emerging that require an integrated analysis. This paper applies Process Integration (PI) tools to investigate opportunities to improve efficiencies in the steam assisted gravity drainage (SAGD) process. The goal of the paper is to design a distributed effluent treatment system to minimize cost and explore the economic-environmental trade-offs based on concepts of Process Integration. Different configurations of water treatment technologies and steam generation options in SAGD operations are assessed and cost, GHG emissions, water and energy consumption are compared across these configurations. The results of the study show that there are potential cost and electricity savings of up to 19.5% and 12% respectively in the water treatment system of SAGD operations relative to “typical” configurations. These results can help oil sands operators make informed decisions about investments in water treatment technologies for SAGD operations.