Cyclic Steam Stimulation Process Research Articles

Investigating the Impact of Hydrocarbon Solvent on In-Situ Asphaltene Precipitation in Solvent-Assisted Cyclic Steam Technique

Summary Heavy oil recovery techniques often confront a significant challenge in in-situ asphaltene precipitation. This procedure significantly affects the characteristics of reservoirs and impedes optimal oil extraction. The purpose of this research was to examine how hydrocarbon solvents affect asphaltene precipitation occurring naturally in the reservoir as well as the resulting asphaltene content in processed oil. This was conducted using a laboratory-level dynamic model and the solvent-assisted cyclic steam stimulation (CSS) method. Throughout this experiment, which comprised six cycles, the steam-solvent blend’s pressure was consistently maintained close to 680 psi and the temperature was maintained at 500°F at the injection point. The findings revealed crude oil cracking at this temperature and noticeable in-situ asphaltene precipitation during the solvent-assisted CSS process. Notably, asphaltenes demonstrated mobility within porous media, contributing to their production in subsequent CSS cycles. Compared to a steam-only CSS control experiment, a higher asphaltene content in the original oil was observed, indicating that thermodynamic changes during the experiments likely caused asphaltene cracking. To sum up, this research provides an understanding of the effects of heavy oil recovery methods that rely on solvents on the precipitation of in-situ asphaltene and the content of asphaltene in the refined oil.

Determination of the main technological parameters of cyclic-steam stimulation of oil reservoirs with account of heat losses along the borehole

Due to the decline in light oil reserves, the development of high-viscosity oil fields has become more relevant today. One of the most common methods of thermal enhanced oil recovery is cyclic-steam stimulation. Compared to other techniques, this method has an advantage of providing higher thermal efficiency due to selection of its parameters with account of variations in the basic properties of a heat carrier as it moves towards the well bottom. The purpose of this work is to create a method for rapid assessment of optimal technological parameters of cyclic-steam stimulation, in which the temperature distributions along boreholes obtained from geophysical research are used as initial data. The created method allows determination of the time of hot carrier injection, steam soak and oil production. The scientific novelty of the study refers to the fact that an integrated approach relating the problem of hot carrier transportation with the problem of determination of optimal parameters for reservoir treatment is proposed for the first time. The cyclic-steam stimulation process is described by the equations of mechanics of multiphase systems. Euler’s method is used to solve the resulting system of equations. The paper presents: functions of depth-wise distributions of pressure, temperature and velocity and dryness fraction of steam; temperature distribution in the multilayer wall of the well and in the rock (considering a specified heat transfer between the layers of the well materials, water and rock at known temperatures); optimal values of the time of hot carrier injection, steam soak and oil production. The calculations have shown that, due to the in the layer of basalt fiber, the temperature in the multilayer wall of the well decreases within 80%. The maximum value of additional cumulative oil recovery has been established by analyzing the calculated bottom-hole parameters of the heat carrier.

The Influence of Interlayer on the Development of Steam Chamber in Steam Stimulation during Heavy Oil Recovery

Cyclic steam stimulation is an effective thermal recovery method for heavy oil recovery. The key potential mechanism is the growth of the steam chamber after steam injection. Taking the LD5X heavy oil reservoir as an example, besides the interlayer developed in this area, the top water and bottom water distribute above and below the interlayer. These factors may have adverse effects on the development of the steam chamber, thus affecting the final heavy oil exploitation. In this work, our goal is to study the effects of interlayer permeability and well–interlayer distance on CSS performance (in the presence of top and bottom water). We developed a high-temperature-resistant interlayer. Based on the simulated interlayer, the field scale model was converted into a laboratory element model through the similarity criterion. In order to quantitatively evaluate the performance of steam stimulation, a thermal detector was used to measure the dynamic growth of the steam chamber and record the production data. The experimental results show that the self-made interlayer has high-temperature resistance, adjustable permeability, and little difference between the physical parameters and the target interlayer. During the cyclic steam stimulation process, the steam chamber presents two different stages in the presence of the top water area, namely the normal production stage and the top water discharge stage. The bottom water has little effect on the growth of the steam chamber. The small interlayer permeability, the increase in horizontal well–interlayer distance, and the existence of the interlayer will delay the top water leakage during steam stimulation. This study has reference significance for us to develop heavy oil resources with a top water barrier when implementing steam stimulation technology.

Experimental Measurements and Numerical Simulation of H2S Generation during Cyclic Steam Stimulation Process of Offshore Heavy Oil from Bohai Bay, China

Cyclic steam stimulation (CSS) is successfully applied to increase heavy oil recovery in heavy oil reservoirs in Bohai Bay, China. However, during the CSS processes, hydrogen sulfide (H2S) was detected in some heavy oil reservoirs. The existing literature mainly focused on the H2S generation of onshore heavy oil. There is no concrete experimental data available, especially about the level of H2S generation during CSS of offshore heavy oil. In addition, there is still a lack of effective reaction kinetic models and numerical simulation methods to simulate H2S generation during the CSS of offshore heavy oil. Therefore, this paper presents a case study from Bohai Bay, China. First, the laboratory aquathermolysis tests were conducted to simulate the gases that are produced during the CSS processes of heavy oil. The effects of the reaction temperature and time on the H2S generation were studied. Then, a one-dimensional CSS experiment was performed to predict H2S generation under reservoir conditions. A kinetic model for the prediction of H2S generation during the CSS of heavy oil was presented. The developed model was calibrated with the experimental data of the one-dimensional CSS experiment at a temperature of 300 °C. Finally, a reservoir model was developed to predict H2S generation and investigate the effects of soaking time, steam quality, and steam injection volume on H2S generation during CSS processes. The results show that the H2S concentration increased from 0.77 ppm in the first cycle to 1.94 ppm in the eighth cycle during the one-dimensional CSS experiment. The average absolute error between the measured and simulated H2S production was 12.46%, indicating that the developed model can accurately predict H2S production. The H2S production increase with soaking time, steam quality, and steam injection volume due to the strengthened aquathermolysis reaction. Based on the reservoir simulation, the H2S production was predicted in the range of 228 m3 to 2895 m3 within the parameters of this study.

A Production Performance Model of the Cyclic Steam Stimulation Process in Multilayer Heavy Oil Reservoirs

Cyclic steam stimulation (CSS) is a typical enhanced oil recovery method for heavy oil reservoirs. In this paper, a new model for the productivity of a CSS well in multilayer heavy oil reservoirs is proposed. First, for the steam volume of each formation layer, it is proposed that the total steam injection volume will be split by the formation factor (Kh) for the commingled steam injection mode. Then, based on the equivalent flow resistance principle, the productivity model can be derived. In this model, the heavy oil reservoir is composed of a cold zone, a hot water zone, and a steam zone. Next, using the energy conservation law, the equivalent heating radius can be calculated with the consideration of the steam overlay. Simultaneously, a correlation between the threshold pressure gradient (TPG) and oil mobility is also applied for the productivity formula in the cold zone and the hot water zone. Afterward, this model is validated by comparing the simulation results with the results of an actual CNOOC CSS well. A good agreement is observed, and the relative error of the cumulative oil production is about 2.20%. The sensitivity analysis results indicate that the effect of the bottom hole pressure is the most significant, followed by the TPG, and the effect of the steam overlay is relatively slight. The formation factor can affect the splitting of the steam volume in each layer; thus, the oil production rate will be impacted. The proposed mathematical model in this paper provides an effective method for the prediction of preliminary productivity of a CSS well in a multilayer heavy oil reservoir.

Optimization of Cyclic Steam Stimulation Process Using Response Surface Methodology

Heavy oil has characteristics such as API gravity 10-20 and high viscosity (100-10,000 cp) at reservoir temperature. Several methods have been successfully applied to produce these reserves, such as cyclic steam stimulation (CSS). Cyclic steam stimulation is a thermal injection method that aims to heat the oil around production wells. This paper presents the investigation regarding CSS application in heavy oil using Response Surface Methodology. Several scenarios were done by varying the operating conditions to obtain the most realistic results and also evaluating the factors that most influence the success of CSS process. Optimization is performed to find the maximum recovery factor (RF) value and minimum steam oil cumulative ratio (CSOR). The operating parameters used are CSS cycle, steam injection rate, and steam quality. Then statistical modeling is carried out to test the most important parameters affecting RF and CSOR for 10 years. The simulation results show that the CSS cycle, steam injection rate, and steam quality affect the RF and CSOR. The maximum RF results with the minimum CSOR were obtained at 39 cycles, an injection rate of 300 bbl/day, and a steam quality of 0.9 with an RF and CSOR value is 24.102% and 3.5129 respectively.

Vertical-well-assisted SAGD dilation process in heterogeneous super-heavy oil reservoirs: Numerical simulations

PetroChina’s Karamay heavy oil reservoirs mostly comprise Jurassic deposits of braided fluvial facies that have a low porosity, extremely high bitumen viscosity, and strong heterogeneities within the reservoir. Steam-assisted gravity drainage (SAGD) dilation start-up has been proven an efficient reservoir geomechanical stimulation method as it shortens the steam circulation time, reduces steam usage, and increases the oil production rates. This method worked well on relatively good-quality oil sand reservoirs. However, for reservoirs with heterogeneous reservoir properties along the SAGD well, field well production data indicated the presence of non-uniform steam chambers in post-dilation SAGD wells. Enhanced dilation methods, such as vertical-well-assisted SAGD dilation (VW-SAGD-Dilation) are have been used, and field pilot tests have yielded promising results. This reservoir stimulation process utilizes one or more vertical wells beside the SAGD well to initiate the formation of dilation zones that connect to the dilation zone formed during the conventional SAGD dilation start-up. Compared with the normal SAGD dilation start-up, this composite dilation process creates a uniform dilation zone along the SAGD well, thus improving the thermal conformance and well productivity. The vertical well and SAGD well are connected by this composite dilation zone, which enables the combined use of the SAGD process and cyclic steam stimulation process. This paper presents our understanding and numerical case studies of this enhanced dilation strategy. The well production data from the post-dilation wells were positive (uniform steam chamber growth and higher oil rate), which highlights the promising potential of using geomechanical dilation as a reservoir stimulation method to create a large stimulated reservoir volume in heterogeneous super-heavy oil reservoirs.

Effect of Temperature on Bitumen/Water Relative Permeability in Oil Sands

The steam-assisted gravity drainage (SAGD) process is among the most applicable thermal enhanced oil recovery (TEOR) methods in North American heavy oil reservoirs. In addition to improving oil mobility through viscosity reduction, the high-temperature condition that a TEOR method causes may significantly alter the fluid flow performance and behavior, as manifested by the relative permeability to fluids in the reservoir. Therefore, in a SAGD and cyclic steam stimulation (CSS), the relative permeabilities can change within the temperature-gradient region developed around the SAGD chamber or between two cycles of CSS processes. However, there is no unique two-phase relative permeability model, especially for bitumen systems to cover a wide range of temperatures. Therefore, the primary objective of this study is to history-match the results of the recent study done by Esmaeili et al. using a new methodology and to conduct limited steady-state relative permeability measurements at different temperatures to confirm the validity of displacement-based relative permeability curves and then to propose a reliable general relative permeability model as a function of temperature. Twelve history-matched bitumen/water relative permeability sets are obtained in a wide range of temperatures from 70 to 220 °C under a confining pressure higher than 1000 psi and the test pressure in the range of 350–400 psi. An in-house developed reservoir simulator was used to obtain relative permeability curves from isothermal displacement data using the history-matching approach. The results demonstrated that both production and pressure-drop data can be matched using the optimized values of parameters of the generalized Corey relative permeability model. Furthermore, a more reliable value for actual residual oil saturation was determined by applying our new methodology in history matching. A comparative analysis with the steady-state relative permeability data allowed us to determine the extent to which the unsteady-state relative permeability is affected by viscous fingering. A considerable shift in both oil and water relative permeability at higher temperatures is noticed. Furthermore, it is also noted that the endpoint relative permeability to oil and water is also altered significantly. The implicit relative permeability data obtained from this study are consistent with the results of the JBN method that were reported in our previous study. By making the parameters of the Corey relative permeability model dependent on temperature, a new model of temperature-dependent bitumen/water relative permeability in sand was developed. It is anticipated that this model can facilitate inclusion of temperature-dependent relative permeability in reservoir simulation studies.

An efficient optimization framework of cyclic steam stimulation with experimental design in extra heavy oil reservoirs

The Jurassic sandstone reservoir of the Pre-Caspian basin has abundant heavy oil resources. It has characteristics of high porosity, high permeability, shallow depth, and high crude oil viscosity. So the cyclic steam stimulation (CSS) is necessary to produce oil in an effective and economic way. However, the optimization of injection-production parameters for CSS is the premise of the technical strategies and development schemes. The conventional method usually adopts the one-parameter-at-a-time approach to perform sensitivity studies. This method is lack of interactions between different factors and difficult to determine the optimal level, in some situations even the main controlling factor is ignored.In our work, the experimental design method was used to consider the interactions of multiple injection-production parameters. The quantitative ranking of important factors was also determined. Based on geological characteristics and pilot test of the extra heavy oil reservoirs in Mortuk oilfield, the numerical simulation model was established. Firstly the two-level Plackeett-Burman experimental design was used to screen seven injection-production parameters for the CSS process. The first five parameters, the sum of their influencing weight larger than 98%, are steam injection intensity, production liquid rate, production time, steam quality and injection rate, respectively. Then the three-level Box-Behnken experimental design was used to perform optimizing studies. Two regression equations of cumulative oil production and cumulative oil steam ratio (COSR) were obtained on the basis of the response surface method, which fits very well with the numerical simulation results. Finally, the optimal values of uncertain factors were determined to maximize cumulative oil with relatively high COSR. This optimization framework is helpful for petroleum engineers to provide a quick evaluation of CSS.

Experimental study on the mechanism of enhanced oil recovery by air-assisted cyclic steam stimulation process in extra-heavy oil reservoirs

ABSTRACTWith the increasing demand of energy, extra-heavy oil has attracted more and more attention at present. Cyclic steam stimulation (CSS) process is one of the main methods to produce extra-heavy oil, however with the increase of stimulation cycle, the periodic oil production of well decreases obviously and the water cut increases significantly. As non-condensable gas, surfactant, high-temperature foam, horizontal well technology, and other assisted CSS methods have been applied in heavy oil reservoirs, it indicates that CSS process has been developing toward diversification. Air-assisted cyclic steam stimulation (AACSS) process has become a more and more popular technique for developing extra-heavy oil due to its abundant sources and low cost. In this paper, static oxidative experiments were carried out to study the mechanism of low-temperature oxidation (LTO) reaction of extra-heavy oil and the effect of temperature, pressure, and catalyst on the LTO reaction. In addition, four groups of CSS experiments were conducted to compare the development performance of different stimulation methods, such as conventional CSS, first-injection AACSS, simultaneous-injection AACSS, and later-injection AACSS. The results show that the system pressure and O2 content decreased, but carbon oxides increased after LTO reaction. The residue O2 content decreased from 21% to below 12% under the safety risk of explosion caused by the mixture of O2 and hydrocarbon gases. During LTO process, both cracking reaction and polymerization reaction of molecule occurred in the extra-heavy oil, which increased the content of saturates and aromatics, while decreased the content of heavy components. LTO reaction also increased the oil viscosity because of the increase of asphaltene content. But pyrolysis reaction would upgrade the extra-heavy oil and decrease the asphaltene content of extra-heavy oil under high-temperature condition. Besides, the higher the reaction temperature and pressure, the faster the reaction and the lower the O2 content. Moreover, the catalyst could enhance the LTO reaction and O2 consumption. Based on the larger scale sand pack experiments, the results indicate that AACSS could effectively improve the oil recovery compared with conventional CSS, and air injection after injecting steam during each cycle could achieve the highest recovery.

Mechanistic simulation study of air injection assisted cyclic steam stimulation through horizontal wells for ultra heavy oil reservoirs

Air injection assisted cyclic steam stimulation (CSS) through horizontal wells is a new technique for the exploitation of ultra heavy oil reservoirs, which has an advantage over other gas or solvent injection processes from the economic point of view. Different from in-situ combustion (ISC) process, the dominating chemical reactions occurring underground in air injection assisted CSS process are low temperature oxidation (LTO) reactions, and owing to the complicated LTO reaction mechanism, this process is still not clearly understood. Therefore, an indepth learning of this process will be of great benefit to its field application and specific project design. In this study, a comprehensive numerical simulation model was established, which accounted for the LTO reactions of different oil components in terms of SARA fractions, as well as permeability reduction induced by coke deposition. A series of simulations were then performed to explore the production performance and elucidate the impacts of various factors. The simulation results demonstrate that air injection assisted CSS using horizontal wells can enhance ultra heavy oil recovery and reduce cSOR in comparison with steam injection alone, which can be attributed to the synergistic effect of steam and air coinjection. Injection of air along with steam can have the same effect as the initial solution gas in reservoir, and the potential of air injection assisted CSS to enhance oil recovery will be more pronounced in oil layers with lean solution gas. In addition, normal air injection can be a viable choice considering the free availability of air, and injection of oxygen-reduced air can become a good option for ultra heavy oils featured with poor LTO reactivity for the sake of safe production.

Energy efficiency and greenhouse gas emissions of current steam injection process and promising steam based techniques for heavy oil reservoirs

Steam injection process has been the prevailing technique for heavy oil and bitumen extraction in the past decades, but the recovery performance and energy efficiency are poor, especially in oil reservoirs with harsh conditions and severe heterogeneity. With global requirements on energy conservation and emission reduction, it is of great significance to improve current techniques or find new techniques to promote the energy efficiency of steam injection process and mitigate associated greenhouse gas emissions. In this study, the energy efficiency and CO2 emissions of current steam injection processes were evaluated, along with sensitivity analysis of various influencing factors. Cyclic steam stimulation (CSS) process was taken as an example to study the production and energy efficiency performance of steam injection. The results show that the steam to oil ratio, energy intensity and CO2 emissions all rise with the increasing crude oil viscosity, but fall with the increase of oil saturation, reservoir temperature, bottom hole steam quality and reservoir heat efficiency. Field history analysis about CSS process shows that the production performance of CSS process was dominated by different factors with the proceeding of oil production, and gas injection assisted CSS process can effectively enhance oil recovery, improve energy efficiency and mitigate CO2 emissions. Finally, the improved steam injection techniques are discussed to shed some lights on the efficient exploitation of heavy oil reservoirs.

Analytical modelling of cyclic steam stimulation (CSS) process with a horizontal well configuration

In this study, a new semi‐analytical model has been developed to model heavy oil production using cyclic steam stimulation (CSS) and horizontal wells. In order to predict oil production, the governing equations of heat and fluid flow in cylindrical coordinate were solved. Average temperature in the formation during the soak period was calculated by solving the transient heat transfer equations. The heat transfer model was then coupled to a fluid inflow model to predict the fluid rates. The developed model is validated with the fine grid numerical simulation of the problem using a commercial numerical simulator. The robustness of the model was tested by comparing the model results with the results from the numerical simulator by changing various parameters such as: steam injection rates, reservoir permeability, relative permeability, oil viscosity, and reservoir thermal diffusivity. With some reasonable assumptions, it was seen that the results from the developed model are very close to the results obtained using the numerical simulator. This paper presents the model development in detail and outlines the steps involved in predicting the performance of a CSS process for a horizontal well configuration.

Numerical study of air assisted cyclic steam stimulation process for heavy oil reservoirs: Recovery performance and energy efficiency analysis

Cyclic steam stimulation (CSS) has been widely applied asan effective technique for heavy oil reservoirs, but it is increasingly concerned in recent years for its limited oil recovery performance, low energy efficiency, high water consumption and great environmental footprints due to greenhouse gas emissions. The hybrid injection of air and steam in terms of low temperature oxidation (LTO) is an innovative technique for the development of heavy oil reservoirs, which can be operated based on the conventional well configuration and was firstly proposed as an enhanced oil recovery (EOR) process for mature heavy oil reservoirs encountered with low reservoir pressure, poor steam sweep efficiency and high water cut. In this study, numerical simulation study is conducted to evaluate the potentials of air assisted cyclic steam stimulation (AACSS) process as an alternative to CSS technique for heavy oil reservoirs. Effects of oil viscosity, LTO reaction and operated air to steam ratio on the well performance are examined for typical heavy oils. The results indicate that AACSS process can effectively improve oil recovery, enhance the energy efficiency and reduce CO2 emissions in comparison with CSS alone, which can be attributed to the thermal effect due to oil oxidation, reservoir repressurization and gas driving offered by air injection, and the AACSS process can be more economically and environmentally attractive than CSS alone. The production performance of AACSS process for ultra heavy oil reservoirs can be more pronounced in comparison with that of ordinary heavy oils, and the LTO characteristics of different oils and the feasible air to steam ratio are reservoir specific for field operation.

Structuring an artificial intelligence based decision making tool for cyclic steam stimulation processes

Cyclic steam stimulation (CSS) is one of the more popular EOR techniques due to the existence of giant heavy oil reserves existing in different parts of the world. Numerical reservoir simulation plays a critical role in investigating the mechanisms and optimizing field development strategies of CSS processes. An artificial neural network (ANN) based model is considered to be a powerful subsidiary tool of high fidelity models for its fast computational speed and reliable prediction capability. This work focuses on the development of a robust surrogate model as a screening/design tool for cyclic steam injection processes using artificial neural network technology.The major contribution of this work includes training of the ANN model using a network topology optimization workflow to help the ANN better understand the complex data structures that are encountered in such processes. The developed ANN model successfully incorporates rock-fluid properties such as relative permeability and temperature dependent viscosity as input parameters together with the other relevant data. Last but not least, the network model utilizes a hybrid structure to adapt to the automatic cycle switching scheme that can be encountered in cyclic steam injection processes. The paper shows that the ANN model can be employed both as a classification tool and a nonlinear regression tool. The model is validated via extensive blind tests against high fidelity simulation models and can be used as a powerful screening and process design tool in global optimization of the process.

Smart completion design in cyclic steam stimulation process: an alternative for accelerating heavy oil recovery

Cyclic steam stimulation (CSS) has succeeded in recovering bitumen and heavy oil. However, after the fifth cycle, the process is no longer effective as indicated by the increasing cumulative steam-oil ratio (cSOR). This paper proposes an improvement to the CSS performance by modifying the completion design. The perforation interval is divided into two parts: upper section (for injection) and lower section (for production). In such design, the injected steam would condense due to heat loss. The steam would then flow to the lower section because of gravity force and the oil starts to produce. The injection-production cycle is managed by an interval control valve (ICV). Simulation results show that the proposed design would reduce the cSOR up to 30% and increase the cumulative oil production by 3.5 times. It is also revealed that the longer the distance between the injection and production sections, the better the steam efficiency. [Received: July 11, 2014; Accepted: March 22, 2015]

Effect of bitumen viscosity and bitumen–water interfacial tension on steam assisted bitumen recovery process efficiency

Abstract Over 80% of Athabasca, Alberta, Canada oil sands deposits are suitable for in-situ bitumen recovery processes. Steam assisted gravity drainage and cyclic steam stimulation processes are commercially implemented with current bitumen production capacity of about 850,000 bbl/d, which is projected to exceed 5000,000 bbl/d in the next two decades. Efficiency of these processes would be improved by reducing the steam-to-bitumen ratio. For this purpose addition of light hydrocarbons into steam as a solvent to reduce bitumen viscosity has been studied for decades with a limited commercial success. As an alternate strategy to solvent co-injection with steam, reduction of bitumen–water interfacial tension by co-injection of a surfactant, such as biodiesel (fatty acid methyl esters), with steam was proposed ( Babadagli et al., 2009 . Use of biodiesel as an additive in thermal recovery of heavy-oil and bitumen. In: Paper 049 Presented at the Canadian International Petroleum Conference (CIPC), 16–18 June, Calgary, Alberta, Canada; Babadagli and Ozum, 2012 . Oil Gas Sci. Technol.: Rev. IFP Energies Nouvelles 67 (3), 413–421). The present study focuses on three issues: (i) viscosity of bitumen in the neighborhood of the edge of the steam chamber using heat conduction models, where bitumen mobility should be controlled by viscosity and bitumen–water interfacial tension; (ii) generate bitumen recovery data, operating the steam chamber as a pressure cooker; where bitumen mobility should be controlled mainly by viscosity rather than bitumen–water interfacial tension, since the influence of the creeping flow of water-condensed steam is marginally small; and, (iii) measure bitumen content at different heights of the pressure cooker test spent core samples to predict bitumen mobility and permeability. Pressure cooker tests were performed using steam, steam and pentane as a solvent at 5%, 10% and 15% of bitumen by mass, and steam and biodiesel as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosages. Our test results showed that solvent, such as pentane, addition reduced bitumen recovery as the dosage of solvent addition increased from 5% to 15% of bitumen. This observation is interpreted that while solvent addition reduces bitumen viscosity it also increases bitumen–water interfacial tension; the overall effect of which results in reduction of bitumen recovery efficiency. When biodiesel was used as a surfactant additive at 0.2% and 0.3% of bitumen by mass dosage, a slightly increase in bitumen recovery efficiency was observed. Bitumen mobility and bitumen permeability values predicted in this study were one order of magnitude smaller than that of the values reported in the literature; probably resulting from reduced bitumen–water interfacial tension, by the activation of natural surfactants contained in bitumen, promoting bitumen mobility in the field operations. Result of the present study suggests that further tests and modeling studies are needed to understand effects of bitumen viscosity reduction by solvent co-injection and bitumen–water interfacial tension reduction by surfactant co-injection with steam on the efficiency of steam assisted bitumen recovery processes.

Field Results for Recovering Oil From a Steam-Project Pressure-Isolation Wall

Summary The Lloydminster, Saskatchewan, area Pikes Peak steam project has been onproduction since 1982. A key part of the development strategy was use of anundeveloped pressure-isolation wall to allow the two halves of the pool to bedeveloped with different time schedules and exploitation processes. Use of thepressure-isolation wall allowed different exploitation options to be used, butduring late project life the oil left in the wall needed to be recovered toenhance project economics. A significant challenge in recovering the oil in thewall was the lack of pressure containment or oil saturation on both flanks,resulting in the need for a gentle recovery process to avoid pushing the oiloutside the wall. On the basis of numerical-simulation results, the recoveryprocess selected for the wall was use of two cyclic-steam-stimulation (CSS)horizontal wells operated in a gentle manner. After the horizontal wells weredrilled, however, temperature logs showed the reservoir surrounding one of thehorizontal wells had already been heated by offsetting steam injection, andthat well has been continually produced at good rates without the need forsteam stimulation. The second new horizontal wall well was initially operatedsuccessfully using the CSS process designed using numerical simulation, butthat well is now also being operated in an external drive mode. The results ofthis field study show that the oil in a wall used to pressure isolate sectionsof a steam-project pool can be recovered economically without pushing the oilinto the adjacent depleted areas by use of processes designed to account forlocal wall conditions.

SAGD-Pair Performance Optimization: A Field Case Study of Recovery Enhancement

Summary Performance of fields under thermal recovery processes has been improved considerably by experimenting with new techniques and innovative operational solutions in heavy-oil and extra heavy oil fields (Butler 1994; Singhal et al. 1998). By far, steam-assisted-gravity-drainage (SAGD) and cyclic-steam-stimulation (CSS) methods have been the most compelling and have shown a successful history in these oil fields (Butler et al. 2000; Butler 2001). At the Celtic heavy-oil field, Husky Energy experienced three phases of optimization over the course of 10 years of recovery. The Celtic field consists of 28 SAGD pairs located in the Lloydminster heavy-oil region that have been in service since 2001. Among these pairs, there are three SAGD pairs (F Pad East) with early productivity challenges in addition to downtime caused by sand production. Following new geological realization and reservoir studies, the injector wells were converted to production wells performing a horizontal CSS process. In 2008, and in an effort to maintain production, a detailed numerical-simulation study was conducted to compare different steam support configurations and the result was justified for field execution. The outcome resulted in four directional steam-injection wells (G Pad) permanently started to support the current horizontal producers. In 2009, the new configuration commenced and is still in operation today. Communication with horizontal wells has been confirmed on one side of the pattern, and it has been extending gradually to the other side as it was investigated in other work (Edmunds 1991; Al-Salhi et al. 1997). Recently, acquired field data suggest that the process is exceeding the expected oil profile and its steam consumption is less than anticipated. The geological review, history of the F Pad East pairs, results of numerical-simulation study, and recommendations are presented in this paper.

Design and Numerical Study of a New Hybrid CSS-SAGD Process Using Horizontal Wells for Recovering Heavy Oil

The cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) processes have extensively been applied as standard methods for Canadian oil sands extraction. Recently, many studies have been concentrated on CSS with horizontal wells and hybrid CSS-SAGD processes. In this article, a new hybrid CSS-SAGD process with two CSS horizontal wells and a single SAGD well is developed and investigated for shallow reservoirs by using the fourth SPE Comparative Solution Project adapted for oil sands reservoirs. Compared with the conventional CSS process, it is shown from simulation results that this new hybrid CSS-SAGD process is a more efficient recovery process.