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As one the most important recovery mechanisms of steam‐assisted gravity drainage (SAGD), gravity drainage is largely dependent on the inclination angle of the steam chamber edge. The existence of solution‐gas causes an ellipsoid‐shaped chamber that has small inclination angle at the bottom, which leads to inefficient gravity drainage and slows down oil production. To address this problem, this study proposes a new scheme, variable‐pressure SAGD (VP‐SAGD). It is basically a SAGD process, at certain stages of which pressure surge is induced by controlling the operating conditions so that the shape of steam chamber can be altered. This leads to a larger slip angle in the steam chamber at the bottom and more efficient heat transport between hot steam and crude oil. Results show that VP‐SAGD is able to increase oil recovery by up to 20% and decrease cumulative steam–oil ratio (cSOR) by up to 7%. Its special oil extraction mechanisms include swabbing effect, enlarged inclination angle of steam chamber boundary at the bottom, and enhanced heat transfer. Particularly, the inclination angle is increased by up to 40%. In addition, a lower producer bottom‐hole pressure (BHP) during pressure drawdown leads to a better production incremental in later stages. The optimal timing for pressure surge is the middle stage of steam chamber growth. The lower the producer BHP decrease, the better the yield increase. Moreover, The VP‐SAGD strategy works better in heavy oil reservoirs with a permeability of k = 0.5–10 Darcy or solution gas content of greater than 2%. [ABSTRACT FROM AUTHOR]

Abstract Steam-assisted gravity drainage (SAGD) is an efficient thermal recovery technique for oil sands and extra heavy oil exploitation. The development of steam chamber goes through multi-stage physical processes for SAGD production in a heavy oil reservoir with an interlayer. In this study, considering the situation that an interlayer is located directly above a pair of horizontal wells, we analyzed the whole process of steam chamber development. We divided the whole process into stages I–V, which are the first rising stage, the first lateral expansion stage, the second rising stage, the second lateral expansion stage and the confinement stage, respectively. Particularly, we further divided stage II into 2 periods and stage IV into 3 periods. These stages and periods can help us understand the development process of steam chamber dominated by an interlayer more profoundly. Based on the divided stages and periods, we established different models of SAGD production by assuming different geometric shapes of steam chamber in different stages and periods. Oval shape was assumed in stages I and III, and inverse triangle shape was hypothesized in stages II, IV and V. The formulas of the front distance of steam chamber and the oil production rate of SAGD were deduced from the established models for different development stages. At the end, we performed two example applications to SAGD production in heavy oil reservoirs with an interlayer. The real oil production rates were matched very well with the theoretical oil production rates calculated by the deduced formulas, which implies the multi-stage development model of steam chamber is of reliability and utility.

The influences of structural parameters (shape, dimensions, structure pitch) on the capillary-transport properties of the wick was studied, and the choice of microstructured wick elements for hyperfine evaporative-condensing devices is substantiated. It has been established that steam chambers with conical microstructures are characterized by minimal mass at a high efficiency in removing thermal loads from hard-to-reach heat-stressed elements. Laboratory technologies for producing microprofiled structures by chemical and electrochemical milling have been developed. Experimental samples of microprofiled structures with a porosity of 65% and a permeability of 91 darcy were obtained. Based on the developed wick (70 × 70 × 0.05 mm3), a steam chamber of size 75 × 75 × 0.81 mm3 (working fluid — water, casing — copper) with a thermal resistance of 0.13 K/W and isothermicity of 1.4°C was created. [ABSTRACT FROM AUTHOR]

As the SAGD steam chamber and production performance in heavy oil reservoirs under fluvial sedimentation environment are heavily impacted by reservoir heterogeneity, an innovative strategy was proposed in this study coupling rock dilation and multi-lateral wells in SAGD projects to break the mud barriers and achieve uniform steam chamber growth. True tri-axial experiments and numerical simulation were designed to validate the feasibility of this strategy, based on which the branches of the SAGD well pairs were designed and the operational parameters were optimized for different geologic heterogeneity conditions. The tri-axial experiment results indicate that the rock formations in the heavy oil reservoirs of the F oilfield exhibit significant shear dilation effects under low confinement pressure conditions, with a volumetric dilation capacity of up to 7%. The branches should be deployed in an interleaved manner, with a horizontal displacement of 20 m and a vertical displacement of 6 m. The optimal results are achieved when the branches intersect the interbeds, allowing for enhanced steam chamber conformance and enlarged volume. Dilation zones of 3–8 m can be created above the steam-injection horizontal wells and around the branches in the reservoir during the dilation of SAGD steam chambers. The maximum volume of dilation fluid used for hydraulic dilation is suggested to be less than 2000 m3. This strategy has been validated as being successful in the pilot SAGD well pair in the F oilfield, China, with the SAGD preheating time reduced by 50% and an incremental oil rate of 4.5 tones/day, indicating encouraging potentials in similar heavy oil reservoirs. [ABSTRACT FROM AUTHOR]

Steam-assisted-gravity-drainage (SAGD) is a widely employed method to enhance heavy oil production and efficiency, and the key to ensuring its steady operation is the maintenance of a steam chamber. Heat conduction and convection of steam to connate water are essential factors in the heat transfer process. In this paper, we developed a novel analytical model to investigate the heat transfer process on the boundary of the steam chamber, driven by the pressure difference between the injected steam and the original reservoir. Both conduction and convection are considered in this new model, and the calculated results are in good agreement with the simulated data by using CMG-STARS. After model validation, the effects of physical properties and operating conditions (relative permeability, initial water saturation, and steam temperature) on the heat transfer process are investigated. The results reveal that connate water saturation plays a large role than the steam temperature in conductive heat flux; low saturation leads to more efficient crude oil exploitation. This work provides new insights into the recovery mechanisms of a SAGD process. [ABSTRACT FROM AUTHOR]

Zhong18 wellblock of Fengcheng oilfield developed with low permeability interlayer and had strong heterogeneity, which caused steam chamber of conventional steam assisted gravity drainage (SAGD) process cannot extend lengthwise continuously and serious steam heat loss. To address this problem, a method of acid fracturing assisted SAGD process is proposed to enhance the oil drainage and improve oil recovery. Based on the herringbone well SAGD being used in Zhong18 wellblock, the orthogonal experimental design and oil reservoir numerical simulation are used to determine the significance level and fracture parameter optimization of the acid fracturing process. The priority of optimization sequence is: fracture permeability, fracture width, fracture half-length, fracture spacing. The optimal parameters are as: 3D fracture permeability, 2.8 mm fracture width, 80 m fracture half-length and 80 m fracture spacing. A 10-year simulation using optimized parameters can improve the recovery by 9.2 % compared with the conventional SAGD process. The result proved that acid fracturing assisted herringbone well SAGD process can effectively penetrate the low permeability interlayer, expand the sweep range of steam chamber, and improve the oil recovery degree of the reservoir. [ABSTRACT FROM AUTHOR]

Thermosensitivity experiments and simulation calculations were conducted on typical oil sand core samples from Kinosis, Canada to predict the steam chamber development with time-lapse seismic data during the steam-assisted gravity drainage (SAGD). Using an ultrasonic base made of polyether ether ketone resin instead of titanium alloy can improve the signal energy and signal-to-noise ratio and get clear first arrival; with the rise of temperature, heavy oil changes from glass state (at –34.4 °C), to quasi-solid state, and to liquid state (at 49.0 °C) gradually; the quasi-solid heavy oil has significant frequency dispersion. For the sand sample with high oil saturation, its elastic property depends mainly on the nature of the heavy oil, while for the sand sample with low oil saturation, the elastic property depends on the stiffness of the rock matrix. The elastic property of the oil sand is sensitive to temperature noticeably, when the temperature increases from 10 °C to 175 °C, the oil sand samples decrease in compressional and shear wave velocities significantly. Based on the experimental data, the quantitative relationship between the compressional wave impedance of the oil sand and temperature was worked out, and the temperature variation of the steam chamber in the study area was predicted by time-lapse seismic inversion.

Geothermal energy is a clean energy source to fulfill the increasing global energy demands. For the first time, several energy extraction strategies are proposed and compared through numerical simulations for effective energy recovery from low-permeability geothermal reservoirs. We simulate geothermal energy extraction using either Cyclic Water Injection (CWI) or Water-Assisted Gravity Drainage (WAGD) processes with or without hydraulic fracturing over a 10-year operation. We evaluate the positioning of injector and producer in WAGD process, well spacing, addition of one injector, and the time variation of injection/soaking periods in CWI process. The simulations indicate that the fractured reservoirs generate more energy than those without fracturing; CWI-based processes exhibit higher energy recovery efficiency than WAGD process in terms of Energy-Water-Ratio (EWR). EWR, as a newly proposed parameter in this study, is defined as the energy production specific to per unit volume of water injected, which is useful in evaluating the cost-effectiveness of a geothermal energy extraction process. The gravitational effect proves to be the dominant factor that determines energy generation compared to phase change in WAGD process. In addition, formation and impacts of steam chambers in CWI and WAGD-based processes are discussed. Furthermore, statistical analyses are performed to evaluate the effects of reservoir temperature, pressure, permeability, and their mutual interactions on cumulative energy production. Eventually, two correlation models for predicting cumulative energy production based on these formation properties are proposed. This study provides a new perspective on implementing different innovative exploration strategies and optimization processes for energy extraction from low-permeability geothermal reservoirs.

Steam injection can be success in increasing oil recovery by determining the steam chamber growth. It will impact on the steam distribution and steam performance in covering hot areas in the reservoir. An injection plan and a proper cyclic steam stimulation (CSS) schedule are critical in predicting how steam chamber can grow and cover the heat area. A reservoir simulation model will be used to understand how CSS really impact in steam chamber generation and affect the oil recovery. This paper generates numerous scenarios to see how steam working in heavy oil system particularly in unconsolidated sand reservoir. Combine the CSS method and steam injection continue investigate in this research. We will validate the scenarios based on the how fast steam chest can grow and get maximum oil recovery. Reservoir simulation resulted how steam chest behavior in unconsolidated sand to improve oil recovery; It concluded that by combining CSS and Steam Injection, we may get a faster steam chest growth and higher oil recovery by 61.5% of heavy oil system.

Flue gas assisted steam assisted gravity drainage (SAGD) is a frontier technology to enhance oil recovery for heavy oil reservoirs. The carbon dioxide generated from the thermal recovery of heavy oil can be utilized and consumed to mitigate climate warming for the world. However, most studies are limited to merely use numerical simulation or small physical simulation device and hardly focus on large scale three-dimensions experiment, which cannot fully investigate the enhanced oil recovery (EOR) mechanism of flue gas assisted SAGD, thus the effect of flue gas on SAGD production performance is still not very clear. In this paper, large-scaled and high temperature and pressure resistant 3D physical simulation experiment was conducted, where simulated the real reservoir to a maximum extent, and systematically explored the EOR mechanisms of the flue gas assisted SAGD. Furthermore, the differences between the steam huff and puff, SAGD and flue gas assisted SAGD are discussed. The experimental result showed that the production effect of SAGD was improved by injecting flue gas, with the oil recovery was increased by 5.7%. With the help of thermocouple temperature measuring sensors, changes of temperature field display that flue gas can promote lateral re-development of the steam chamber, and the degree of reservoir exploitation around the horizontal wells has been increased particularly. What's more, the addition of flue gas further increased the content of light components and decreased the content of heavy by comparing the content of heavy oil components produced in different production times. [ABSTRACT FROM AUTHOR]

The paper is devoted to the development of models and methods to describe and predict the process of steam-assisted gravity drainage during the extraction of high-viscosity oil. On the basis of the original physicomathematical model, the authors have considered the problems of circulation of a steam in the injection well for preheating the stratum, the stratum sweep by the action of the steam, and methods to increase it. The presence of the optimum spacing between pairs of reactive wells or the optimum density of the network of wells has been established. From an analysis of basic mechanisms of the process, the authors have identified the causes of the maximum value of the oil recovery factor for the optimum network of wells. The possibility has been shown of raising the economic efficiency of the process of passage from the injection of a steam to the injection of unheated water in the final stage of the process. [ABSTRACT FROM AUTHOR]

The steam chamber rising process is an essential feature of steam-assisted gravity drainage. The development of a steam chamber and its production capabilities have been the focus of various studies. In this paper, a new analytical model is proposed that mimics the steam chamber development and predicts the oil production rate during the steam chamber rising stage. The steam chamber was assumed to have a circular geometry relative to a plane. The model includes determining the relation between the steam chamber development and the production capability. The daily oil production, steam oil ratio, and rising height of the steam chamber curves influenced by different model parameters were drawn. In addition, the curve sensitivities to different model parameters were thoroughly considered. The findings are as follows: The daily oil production increases with the steam injection rate, the steam quality, and the degree of utilization of a horizontal well. In addition, the steam oil ratio decreases with the steam quality and the degree of utilization of a horizontal well. Finally, the rising height of the steam chamber increases with the steam injection rate and steam quality, but decreases with the horizontal well length. The steam chamber rising rate, the location of the steam chamber interface, the rising time, and the daily oil production at a certain steam injection rate were also predicted. An example application showed that the proposed model is able to predict the oil production rate and describe the steam chamber development during the steam chamber rising stage. [ABSTRACT FROM AUTHOR]

Steam-assisted gravity drainage (SAGD) is an efficient technology that has been used to develop oil sand resources, and it has been successfully and maturely applied in Canada. However, oilfield production has demonstrated that reservoir heterogeneity has a serious impact on SAGD development, among which the most drastic impact is caused by multiple barrier layers in the reservoir. These barrier layers can severely impede the development of a steam chamber and the drainage of oil. Hence, it is important to investigate their influence mechanism. In this study, oil samples from the Long Lake oil field were used in laboratory experiments to study the development of the steam chamber and the residual oil distribution under the effect of multiple barrier layers. Then, a theoretical numerical simulation model was established to describe the fluid flow more precisely. In addition, the production characteristics of SAGD under the influence of different numbers of barrier layers were analyzed by comparing the development of the steam chamber. Finally, the impacts of multiple barrier layers with different modes of combinations were studied for their effects on SAGD production. The results indicated that for impermeable barrier layers of the same length, the steam primarily developed upward after flowing around the first barrier layer. After the steam chamber reached the top of the reservoir, the steam began to enter into the interbedded zone. Based on an unchanged first barrier layer, the number of barrier layers had little influence on the overall shape of the steam chamber and SAGD production, which confirmed that the first barrier layer played a dominant role in the influence of multiple barrier layers. In addition, characteristic points (P 1 , P 2 , P 3), which corresponded to changes in the stage of steam chamber development, were established and used to evaluate the effect of the barrier layers. Different combinations of barrier layers were realized by changing the relative properties of the first barrier layer. The results showed that the longer the length of the first barrier layer, the closer it was to the steam injection well and the lower the permeability; hence, the more obvious its hysteresis effect on the SAGD process. • A physical model is used to study the effect of multiple barrier layers on SAGD. • A theoretical numerical model is established to describe the fluid flow more precisely. • The first barrier layer plays a dominant role in the influence of multiple barrier layers. • Several characteristic points (P 1 , P 2 , P 3) on the productivity curve are established. • The impact of multiple barrier layers with different combinations is analyzed in detailed. [ABSTRACT FROM AUTHOR]

Worldwide, new techniques to implement Enhanced Oil Recovery in heavy oil reservoirs have been studying, since as most of the global reserves are of this type of hydrocarbon. The Steam Assisted Gravity Drainage (SAGD) is a cutting age EOR method that have been applied in bitumen reservoirs gaining successful results, obtaining recovery factors up to 50%. The technique involves two horizontal wells, the first one located a few feet above the second one depending on the viscosity of the crude oil; by the upper well, the continuous vapor injection is made an for density differences this vapor tents to expand to the top of the formation heating the hydrocarbons which then, by gravity come down in the reservoir to be produce, with the condensed vapor, through the second horizontal well. The production mechanism evidenced in this technique is the gravity drainage because in its implementation, applied to bitumen, only the heated hydrocarbons will flow through the producer well by the effect of the gravity therefore a connectivity between the two wells must be necessary. However, in the majority of heavy oil reservoirs the crude have mobility i.e. the viscosity is not to high (

Deeply-buried and high-bitumen-content crude oil is one of the most important energy resources. Currently, Steam- and Solvent-Assisted Gravity Drainage (SSAGD) is an attractive, but a high-cost and high-carbon-emitting method for exploiting this type of resource. In order to evaluate the greenhouse gas (GHG) emission and economic performance of SSAGD, it is critical to predict the energy efficiency and solvent retention in the steam chamber. However, the fluid property profiles inside the steam chamber, which are directly related to energy efficiency and solvent retention, have been rarely investigated. In this work, a semi-analytical model is developed for examining the property distributions within the steam chamber, considering the complex interaction of energy and mass transfer along with the effects of phase behavior. Subsequently, the solvent retention and energy-utilization/-saving efficiency are carefully analyzed on the basis of the calculated property profiles inside the steam chamber. The proposed method is mostly based on analytical relationships and is free from certain simplifications that may affect the calculations of energy efficiency and solvent retention in the SSAGD process. Furthermore, the optimal solvent type and injection pressure obtained with the model can reduce the GHG emission and improve the economic benefits of future SSAGD projects. [ABSTRACT FROM AUTHOR]

Steam assisted gravity drainage (SAGD) method for heavy oil exploitation using horizontal wells has been done and successful in the field. In the similar concept with SAGD using horizontal wells, vertical well SAGD has been developed as alternative method. This well consists of two strings where one is as a producer on the bottom and the other one is as an injector on the top. This investigation makes different distance between injector and producer perforations gradually. The aim of this research is to make optimization strategy on the vertical well SAGD. The sensitivities tested consist of injection rate and distance between producer and injector perforations. Analysis result reveals that the impact of multilevel injector will decrease cSOR and improve the production rate on the same injection rate. If the process is combined with multilevel injection rate, the result would offer the most favourable option. Furthermore, the longer distance between producer and injector perforations will cause longer restrained heat in reservoir so that the volume steam chamber will be bigger and drainage radius will be wider. [ABSTRACT FROM AUTHOR]

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An analytical model for estimating the discharge of a horizontal well in the process of mining deposits of superviscous oils and natural bitumens by the method of steam-assisted gravity drainage has been developed. The results of calculations carried out using this model are in good agreement with the corresponding data of experiments on the physical simulation of the process of steam-assisted gravity drainage. The infl uence of the fi ltration capacity and the linear sizes of an oil pool on the discharge of a horizontal well in it was investigated. [ABSTRACT FROM AUTHOR]

The Guantao Formation in the Block Du 84 of the Liaohe Oilfield of Northeastern China is a super heavy oil reservoir surrounded by top water, side and bottom water. Commercial development started in 1999 using vertical well Cyclic Steam Stimulation (CSS), with anticipated oil recovery factor of less than 25%. To improve the ultimate oil recovery, a pilot test of SAGD as a follow-up to CSS began in 2005 using a combination of infill horizontal wells with existing vertical wells; and the commercial expansion began in 2008 as a result of the encouraging results from pilot test. The current recovery factor over the entire development area has exceeded 45% of OOIP, with the pilot test area exceeding 68% of OOIP, and the ultimate recovery factor is predicted to exceed 70%. As the steam chamber becomes more mature and continues expanding upward, the risk of communication with the top water increases. Due to high pressure (>6.0 MPa) in the top water layer, it is not practical to balance the operating pressure in the steam chamber under the current economic conditions. The early forecasting of top water flow rates is important to assess its potential impact on SAGD performance and to formulate operating strategies for the late stage of SAGD development. In this paper, a theoretical model for predicting flow rate of top water to the SAGD chamber is established based on the incorporation of fluid flow and heat transfer mechanisms in porous media in the reservoir (barrier layer) between the steam chamber and the top water. The influence of barrier layer thickness, permeability, crude oil viscosity distribution and operating pressures in the steam chamber on the flow rate of the top water are studied. The flow of the top water into the steam chamber will lower oil to steam ratio (OSR) and the recovery process may become uneconomic when top water flow rate exceeds the current steam injection rate per well pair. The presence of high-viscosity "asphalt shell" layers near the bottom of the top water has limited mitigation effect on the flow of the top water. Under current operating conditions and 3.0 MPa pressure differential between the top water layer and steam chamber, 10 m of minimum thickness of barrier layer should be maintained to effectively mitigate the risk from inflow of top water. • A predictive model is established for the flow rate of top water into the steam chamber. • Key parameters affecting flow rate of top water into the steam chamber are analyzed. • The effect of top water flow into the steam chamber on OSR is evaluated. • Recommendations are made for mitigating the impact of top water on SAGD operations. [ABSTRACT FROM AUTHOR]

Steam injection is the most popular used method in recovering heavy oil reservoirs. Many researchers were engaged in enhancing oil recovery (EOR) methods by using various well configurations. Laboratory experiments and field applications have verified the feasibility of extra-heavy oil recovery by steam injection using vertical injector -horizontal producer. It was also referred to as a steam assisted gravity drainage (SAGD) process. However, the characteristic of steam chamber growth and production performance during the vertical injector-horizontal producer steam injection process have not been fully understood. In this study, a 3D physical model was constructed to investigate the mechanisms of the steam injection process using vertical injector-horizonal producer. Numerical simulations were also conducted to verify the laboratory experiment and field application. In the aspect of steam chamber growth, the results revealed that three stages were included during the steam injection process. In the aspect of developing mechanisms, it can be divided into steam flooding and gravity drainage stages. Moreover, the results show that about 43.9% of original oil in place (OOIP) was produced in the gravity drainage stage. In addition, subcool showed significant difference in steam flooding and gravity drainage stages. The temperature distribution mode of the horizontal producer was analyzed and proved to be a significant factor that influences the production performance. Sensitivity analysis by using numerical simulation demonstrated that oil viscosity is the dominant factor that impact the production performance. The results guided the development of pilot test area in Xinjiang Oilfield, China. The study can provide a clearer understanding of the vertical injector-horizontal producer steam injection process in recovering heavy oil reservoirs. • The vertical injector- horizontal producer steam injection process was divided into three stages. • The dominant driving forces, steam flooding and gravity drainage, varies in different developing stages. • Production performance at different developing stages were analyzed, and most oil was developed by gravity drainage. • The results were used to guide the development of the pilot test area in Xinjiang Oilfield. [ABSTRACT FROM AUTHOR]