Steam Assisted Gravity Drainage Wells Research Articles

A Simple Normalized Analytical Model for Oil Production of SAGD Process and Its Applications in Athabasca Oil Sands

Summary Since the late 1980s, when the Alberta Oil Sands Technology and Research Authority Underground Test Facility project first demonstrated the feasibility of the steam-assisted gravity drainage (SAGD) technology, many commercial SAGD projects were brought online in Western Canada. Now, many of these projects have late-life SAGD wells approaching their ultimate SAGD recovery factors. Although these projects have demonstrated highly variable production performance, there is an opportunity to use the industry production data to find what they have in common and develop a normalized SAGD model. For this paper, we collected oil production history from several leading SAGD projects with late-life production in the Athabasca oil sands area and confirmed the three stages in an SAGD project lifespan: chamber rising, chamber spreading, and chamber falling stages. By normalizing the field data, all SAGD projects converged to one type curve, regardless of reservoir quality and operating conditions. Based on this observation, a new simple normalized model is derived to model the bitumen production in a typical SAGD process for Athabasca oil sands. The new model bridges the gap between the existing SAGD analytical model and conventional decline analysis and provides oil production forecasts based on the inputs for the five-component recovery factor method defined in the Canadian Oil and Gas Evaluation Handbook(Society of Petroleum Evaluation Engineers 2018). The model has been applied to one of the thermal projects to history match the field production. By running a Monte Carlo simulation, this model further demonstrates its capability to capture the uncertainty of the production forecast for the project at different stages of SAGD operation. In addition, by properly modifying the type curve of the analytical model, a similar workflow can be used to model cases with special reservoir quality or different operational limitations.

Experimental Study and Numerical Simulation of an Electrical Preheating for SAGD Wells in Heavy Oil Reservoirs

It is necessary to establish effective communication between two horizontal wells during the preheating period of steam-assisted gravity-drainage (SAGD). However, the preheating time is usually very long, which results in high steam consumption and CO2 emissions. There is little research on the effects of different wellbore fluids during the preheating period. The heat transfer and heating characteristics of different wellbore fluids–water, heat-conduction oil, and air–were explored by using physical experiments and numerical simulations. In this study, the results indicated that the heat-transfer performance of heat-conduction oil is the best. The numerical simulation’s results indicated that compared with the wellbore saturated with water, the heat-conduction oil reduced the viscosity of crude oil, and energy consumption was not obvious during the preheating stage. The super-heavy oil flowed into the wellbore due to the solubility of the heat-conduction oil and its own gravity. As a result, the super-heavy oil content in the wellbore gradually accumulated, increasing the risk of coking. Those experiments showed that the use of electrical heating provides good potential to improve SAGD efficiency during the preheating period, and water is the best injection fluid for wellbores during the electrical heating process.

Subsurface waste heat recovery from the abandoned steam assisted gravity drainage (SAGD) operations

A considerable fraction of the energy injected during the thermal recovery of oil remains in the subsurface and wasted in the surrounding geological formations after the profitable life of oil wells is over. This work studied the concept of thermal energy extraction from the abandoned SAGD operations in oil sands reservoirs for generating electric power. The cold water is injected as a working fluid to extract heat after the oil production is ceased, and the produced hot water is fed to a surface binary cycle to generate electric power. The results show that an oil sands reservoir after SAGD operations could be regarded as an artificial geothermal system suitable for thermal energy extraction. It is demonstrated that a total net electric energy output of 57 GWh could be achieved based on a single SAGD well pair during a ten-year heat-extraction time, indicating the huge heat extraction potential at full field scale. The results show that the thermal energy conversion efficiency to electricity for the abandoned SAGD wells can reach as high as 12%. The demonstrated subsurface waste heat recovery from the abandoned SAGD sites revealed that between 15 and 36% reduction in CO2 emission could be achieved.

Coupled geomechanical-thermal simulation for oil sand reservoirs with shale barriers under hot water injection in vertical well-assisted SAGD wells

Mudstone stringers in an oil sand reservoir can significantly affect the propagation of the steam chamber in the process of steam-assisted gravity drainage (SAGD). The micro-fracturing by water injection in strongly heterogeneous oil sands can result in these problems such as hard stringer breakthrough and aggravating heterogeneity. This paper proposed a comprehensive numerical model for conventional SAGD wells and vertical well-assisted SAGD (VWA-SAGD) wells to predict the coupled thermo-hydro-mechanical responses under hot water injection in a typical Karamay oil sand reservoir with two stringers, considering skeleton shear dilation, the ''phase change'' of bitumen, formation heterogeneity, the permeability evolution induced by elastoplastic deformations, and the theory of heat and mass transfer. Major conclusions were drawn that there are three relatively narrow separate transition zones effectively heated around the SAGD wells and vertical well. The vertical well makes about 0.5 MPa increase to the pore pressure of the reservoir embedded with mudstone stringers in vertical directions and rises by about 0.6 MPa for the reservoir pore pressure above the upper stringer to reduce the pore pressure differential along the wellbore. Water injection-induced ultimate stress states can't reach the shear failure line under field operations, so the shear dilation can't be induced. The thermoporoelastic deformation determines whole reservoir deformation. The reservoir between the two stringers contributes to most of the caprock uplift. The VWA-SAGD technique can improve the porosity by about 1% in the whole vertical direction and reduce the anisotropy of porosity along the wellbore, which is beneficial to the uniform and fast propagation of the steam chamber in subsequent preheating and production stages. These findings can be employed to accurately predict the temperature, pore pressure, stress/displacement, and porosity evolutions for the field engineers to properly evaluate the uplift of reservoir and caprock, oil output changes, and heat utilization efficiency.

Steam conformance investigation of flow control devices deployed in SAGD injection and production horizontal wells

The nonuniformity of the steam chamber has a significant influence on oil recovery in the process of Steam-Assisted Gravity Drainage (SAGD). To improve steam conformance, Flow Control Devices (FCDs) are generally installed in both the SAGD injector and producer. In this paper, we investigated the steam conformance of tubing-deployed FCDs in a SAGD well pair. First, a three-phase, three-dimensional reservoir model was developed. Then, a wellbore model for saturated steam flow in the FCD equipped injector and oil/water flow in the FCD equipped producer was proposed. Next, the reservoir and wellbore models were coupled and solved fully implicitly. Finally, after model validations, the effects of the steam injection mode, FCD parameters, steam injection parameters and reservoir geological properties on the conformance of the steam chamber were studied. The results showed that tubing-deployed FCDs were obviously better at improving the steam conformance than the simultaneous dual-tubing string injection technique and injecting steam at only a single point. The steam chamber conformance increased with a decrease in steam injection pressure and reservoir permeability and an increase in steam quality and oil saturation. The steam chamber uniformity gradually declined with time. To maintain the steam conformance over the life of the SAGD and ultimately oil recovery, the FCD open flow area design in SAGD wells should be adjusted at different injection times. When the FCD open flow area was small in the part with high permeability and large in the part with low permeability, a high degree of steam conformance and greater amount of cumulative oil production could be obtained.

A review of fines migration around Steam Assisted Gravity Drainage wellbores

This paper reviews the state-of-the-art experimental and theoretical methods on fines migration around Steam Assisted Gravity Drainage (SAGD) wellbores. The in-situ migratory particles can deposit in the pore space and result in pore throat plugging within the porous medium. This process damages the permeability around the sand control screen. This review includes field observations, experimental works, and simulations solving fines migration mathematically. Field observations indicate higher pressure differentials between the SAGD injector and producer due to the plugging of the sand control screen and surrounding formation. Coreflooding experiments confirm that the fines migration process is an essential contributing factor to the permeability damage near the SAGD wellbores. Macroscopic analytical models have also been extensively used at the lab-scale to predict the permeability variation by the fines migration. The modeling studies are focused mainly on consolidated sandstones, but the impact of sand control devices has not been incorporated. Many papers have been published to describe the influential factors controlling the fines migration process. However, the interaction between the wellbore completion and surrounding sand from the fines migration perspective has not been adequately explored. Despite numerous limitations in representing the reality near the SAGD wellbores, sand control testing procedures provide a short-term evaluation of the sand retention and flow performances of the sand control device in unconsolidated sand. However, these tests do not account for the transient behavior and long-term permeability variation caused by the fines migration process. This paper presents an integrated general-purpose procedure for the design of sand control devices in SAGD wells, addressing the gaps from this review.

Technology Focus: Heavy Oil (April 2021)

After serving two terms for a total of 6 years, my time writing this column is coming to an end. This issue of JPT marks my last opportunity to share my thoughts, recap my observations, and make note of some final touch-ups to the research conducted over this 6-year period with regard to recent heavy oil practices. Here are some highlights to keep in our minds over the coming years. Despite all the recent negative and serious changes affecting the whole world and our industry, life goes on and we will increasingly be needing energy. One should recall that statistics predict oil will continue to be the main source of energy for the next 2 decades, with heavy oil constituting a great portion of that. That means that, while the oil industry is going through unprecedented and even unpredictable economic downturns, the status of heavy oil is still unquestionable. However, we have to face the fact that this energy should be tapped in a cheap, clean, and sustainable way. The best aspect of this effort is that heavy oil technologies have been established and tested over a long period of time, unlike other unconventional resources. Lowered steam consumption, down to zero if possible, has been under consideration to minimize the emission of greenhouse gases (GHGs) while simultaneously producing heavy oil. This green effort leads us to nonsteam techniques such as the use of water with chemicals (mainly polymer) and noncondensable gases and certain unconventional methods such as solvent injection and electromagnetic heating, the latter being unavoidable especially for extraheavy oil and bitumen. These areas have been critically considered by researchers and practitioners with a considerable number of applications existing at the field scale. At the same time, the oil industry must deal with mature steam projects in the near future. We have accumulated so much heat energy over the decades, yet a substantial amount of oil remains in these reservoirs. What can be done to reuse this energy? Can we recover different forms of energies using methods with no GHG emission? The current practices encountered in field-scale operations to improve the heavy oil recovery in mature steam applications use noncondensable gases; mainly, these techniques serve to pressurize steam-assisted gravity drainage wells, improve sweep and microscopic displacement by adding chemical additives to the steam (or hot water), and re-engineer well designs (flow control for efficient heating and sweep). My final example highlighting new practices is the increasing trend of offshore heavy oil practices. Of particular interest is polymer injection through vertical and horizontal wells and pilot steam applications, methods that are effective even if they occur at the pilot stage of the process. Recommended additional reading at OnePetro: www.onepetro.org. SPE 199947 - Enhanced Oil Recovery in Post-Cold Heavy Oil Production With Sand Heavy Oil Reservoirs of Alberta and Saskatchewan Part 2: Field Piloting of Cycling Solvent Injection by Gokhan Coskuner, Consultant, et al. SPE 199925 - Scalable Steam Additives for Enhancing In-Situ Bitumen Recovery in SAGD Process by Armin Hassanzadeh, Dow, et al. SPE 199927 - The Myth of Residual Oil Saturation in SAGD - Simulations Against Reality by Subodh Gupta, Cenovus Energy, et al.

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.

Investigation on Tripping in Magnetic Generator in Steam-Assisted Gravity Drainage Wells Based on Numerical Simulation

Abstract Magnetic Guidance Technology can meet the precise measurement requirements when drilling steam-assisted gravity drainage (SAGD) oil wells. Magnetic generator is a key part in the Magnetic Guidance Technology. When magnetic generator is tripped into horizontal well, pump pressure and passing capacity of the magnetic source generator in the curved section need to be analyzed. So, a mathematical model of tripping in the magnetic generator is established. If curvature radius, deviation angle, and friction factor are known, the forces acting on the magnetic generator in different positions could be calculated. The finite element (FE) results show that: (1) with depth increasing in the curved section, the equivalent stress on the magnetic generator increases in a fluctuating manner, the contact area, friction drag, and energy loss increase. (2) The greater the hole curvature, the greater tripping in force and the higher pump pressure are needed. The lower friction coefficient is favorable to tripping in the magnetic generator. (3) The friction between the magnetic generator and tubing wall in the horizontal section is much less than that in the curved section. Field applications have shown that the maximum downforce is close to the result of finite element analysis. The research results provide a reasonable reference basis for smooth running of magnetic source generators with different trajectory conditions.

An Improved Set of Design Criteria for Slotted Liners in Steam Assisted Gravity Drainage Operation

Slotted liners are widely used in steam-assisted gravity drainage (SAGD) wells to control sand production and sustain wellbore productivity. The slotted liner can provide desirable performance when appropriately designed. A literature review indicates a limited number of studies that offer design criteria specifically for SAGD wells. Moreover, past criteria seem to neglect some key factors, which may lead to inadequate slot design. This paper proposes a set of graphical design criteria for slotted liners in SAGD production wells, using prepacked sand retention testing (SRT) data. The SRT is designed to incorporate several essential factors that are not present in the past design criteria, such as slot density, steam breakthrough, and particle size distribution (PSD). The proposed design criteria are presented graphically for normal and aggressive conditions, where the aggressive condition accounts for the potential occurrence of the steam breakthrough. It is found that the upper bound of the design window is substantially lower for the aggressive condition due to the higher sand production after the steam breakthrough. The design criteria also indicate that the slotted liner is suitable only for the formations with low fines content.

A Novel sand control testing facility to evaluate the impact of radial flow regime on screen performance and its verification

Optimum design of the sand control devices in oil sand reservoirs plays a vital role in minimizing the sand production and increasing the reservoir productivity in Steam-Assisted Gravity Drainage (SAGD) operations. Various sand control testing facilities have been developed to evaluate the performance of sand control screens, such as the pre-packed Sand Retention Test (SRT). Current testing apparatuses are based on the linear flow regime. However, fluid flow around SAGD production wells is radial flow, not linear. This study introduces a Full-scale Completion Test (FCT) facility to emulate the radial-flow condition in SAGD wells. Instead of using a disk-shaped screen coupon, this facility utilizes a cylindrical-shaped screen. A couple of tests were carried out to determine the flow uniformity inside the cell and identify the test repeatability. Test results show that flow is distributed uniformly inside the cell, and experiments are repeatable in terms of differential pressures, fines production, and sanding levels. Therefore, this innovative FCT experimental setup and procedure allows a more realistic evaluation of the liner performance by emulating the real SAGD flow regime around the liner. Testing results obtained from the FCT can be used to complement and validate the current testing procedures. These tools can be adopted for an objective custom-design and selection of standalone screens in SAGD.

The application of geomechanical SAGD dilation startup in a Xinjiang oil field heavy-oil reservoir

Steam-assisted gravity drainage (SAGD) methods have been widely applied in oil-sands exploitation globally. SAGD processes are effective only after thermal and hydraulic communication between the injector and producer has been established during the start-up operation of the well pair. The geomechanical SAGD dilation startup has been considered a promising technology that can enhance permeabilities of heavy-oil reservoirs and reduce thermal conformance time. However, limited studies have focused on the practical operational procedures of geomechanical SAGD dilation startup. This paper presents the application of SAGD dilation startup technology in a shallow super heavy-oil reservoir in the Karamay oil field, China. The general reservoir geology and geomechanical characteristics were investigated and used to propose a practical approach to determine dilation initiation pressure. We also summarize the SAGD well completions and geomechanical SAGD dilation startup procedures. A case study using a real SAGD well is presented and analyzed. We then share the field operation procedures and results after dilation startup. The objective of the research was to reduce the steam circulation time and achieve uniform thermal conformance along the SAGD well. Our field results highlight the promising potential of using water injection to create a dilated zone and dramatically enhance reservoir permeability. The performance of SAGD dilation startup in the Karamay oil field is evaluated by comparing the cumulative oil production rate with those from SAGD wells using conventional startup.

Porothermoelastic response of an oil sand formation subjected to injection and micro-fracturing in horizontal wells

Stimulation of unconsolidated formations via horizontal wells has seen its vast implementation in the recent development of heavy oil reservoir to save the time and cost of preheating the reservoir before the steam-assisted gravity drainage (SAGD) process. A mathematical approach was proposed in this research that fully couples the hydraulic, mechanical and thermal responses of unconsolidated sandstone formations and also applies failure criteria for describing either shear dilation or tensile parting mechanism that generates microcracks. The approach was implemented to predict the porothermoelastic response of a pair of SAGD wells subject to injection and subsequent micro-fracturing using hot water. It was found that the predicted bottom hole pressures (BHPs) match closely with the field observed data. An elliptical dilation zone developed around the dual wells with relatively high pore pressure, porosity, permeability and temperature, implying good interwell hydraulic communication between both wells. The activation of microcracks dramatically accelerated the dissipation of pore pressure across the entire formation depth and also facilitated heat convection in between the dual wells, though to a lesser extent. In summary, the approach provides a convenient means to assist field engineers in the optimization of injection efficiency and evaluation of interference among multiple horizontal wells.

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.

Gap Metric Based Performance Assessment of Subcool Control in Steam Assisted Gravity Drainage Wells

Steam assisted gravity drainage (SAGD) is a widely adopted oil extraction technique for heavy oil reservoirs in Alberta, Canada. One of the common approaches by which the producers optimize the production from SAGD reservoirs is by controlling the emulsion level above the producer well bores, a strategy known as subcool control within the industry. In this study, we assess and compare performances of two subcool control strategies, one of which makes use of classic control strategy (PID) and the other is of advanced control strategy (model predictive controller (MPC)). As the controlled process in this case is a non-linear process, we propose a gap metric-based control performance assessment (CPA) method. By this method, the local models as well as their associated weights are determined using the gap metric. We show that the MPC-based strategy outperforms the PID loops-based strategy in subcool control application.

Modeling of reservoir temperature upon preheating in SAGD wells considering phase change of bitumen

Steam circulation prior to production is usually employed to establish inter-well thermal communication and create an expected initial steam chamber in the process of bitumen recovery using steam assisted gravity drainage (SAGD). To realistically evaluate the efficiency of steam circulation, and to find the indicator for terminating the steam circulation and switching to SAGD production, modeling of the temperature propagation considering the bitumen-rich oil sand reservoir properties and oilfield operations is required. This study proposed two new modified methodologies, including an analytical model as well as a numerical model, in which the latent heat effect caused by the phase change of bitumen was involved for thermo-phase change coupled analyses. The modeling was conducted for a real SAGD steam circulation project in an oilfield located in Karamay, northwest of China, using oilfield operation parameters and thermo-dynamical properties obtained from laboratory tests. The models can predict the temperature propagation and bitumen phase change behavior in the domain encompassing dual wells. In general, the predicted results obtained from both analytical and numerical approaches agree well with those in published articles in terms of the cooling time derived from temperature falloff tests and inter-well midpoint temperature. The modeling draws major conclusions that the temperature drops rapidly with the distance to wellbore in the fusion zone, but decreases slowly in the solid zone. The heat flux on wellbore exhibits an exponential reduction in the beginning, but ultimately tends to be a constant. The moving speed of phase change interface decreases with injection time, and finally increases up to only a short distance. The inter-well midpoint temperature is heated to exceed the threshold temperature, and the whole inter-well area is ultimately occupied by the fusion zone. These findings not only can provide a criterion for evaluating the efficiency of steam circulation and an indicator for terminating the steam circulation and switching to production, but also the approaches proposed may be used to analyze these heat injection and phase change problems occurring in other types of oil and gas-rich reservoirs like the natural gas hydrate formation.

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.

Heavy Oil Recovery Using In Situ Steam Generated by Thermochemicals: A Numerical Simulation Study

This paper introduces a novel approach to generate downhole steam using thermochemical reactions to overcome the challenges associated with heavy oil resources. The procedure developed in this paper is applied to a heavy oil reservoir, which contains heavy oil (12–23 API) with an estimated range of original oil in place (OOIP) of 13–25 billion barrels while its several technical challenges are limiting its commercial development. One of these challenges is the overlying 1800–2000-ft thick permafrost layer, which causes significant heat losses when steam is injected from the surface facilities. The objective of this research is to conduct a feasibility study on the application of the new approach in which the steam is generated downhole using the thermochemical reaction (SGT) combined with steam-assisted gravity drainage (SAGD) to recover heavy oil from the reservoir. A numerical simulation model for a heavy oil reservoir is built using a CMG-STARS simulator, which is then integrated with a matlab framework to study different recovery strategies on the project profitability. The design and operational parameters studied and optimized in this paper involve (1) well configurations and locations and (2) steam injection rate and quality as well as a steam trap in SAGD wells. The results show that the in situ SGT is a successful approach to recover heavy oil from the reservoir, and it yields high-project profitability. The main reason for this outperformance is the ability of SGT to avoid the significant heat losses and associated costs associated with the surface steam injection.

Effect of stress build-up around standalone screens on the screen performance in SAGD wells

Steam Assisted Gravity Drainage (SAGD) is the primary thermal recovery technology currently employed to extract heavy oil and high-viscosity bitumen from Alberta oil sands. In the near-wellbore region, the initial stresses are nearly zero, and as the SAGD chamber grows, the stresses tend to build up due to the thermal expansion of the formation. Also, melting of the bitumen and subsequent loss of the bonding between the grains leads to the collapse of the gap between the formation and sand control liner over time. The result will be effective stress buildup and gradual compaction of the oil sands around the liner.Slotted liners have been extensively used as a sand control device in SAGD wells. Slotted liners must allow free flow through the slots with minimal plugging and acceptable amounts of sand production.In our study, large-scale unconsolidated sand was packed over a multi-slot coupon of the slotted liner. The sand-pack was subjected to several stress conditions corresponding to the evolving stress conditions during the life cycle of a SAGD producer well. The testing program employed several multi-slot coupons to examine the flow performance under typical encountered stresses in SAGD wells. Cumulative produced sand was measured at the end of testing as an indicator of the sand control performance. The permeability evolution of the sand in the near-coupon zone was calculated by measurements of pressure differentials and considered as a measure of screen flow performance. Fines/clay concentration along the sand-pack was also quantified after the test to investigate the fines migration, a phenomenon which is considered to be the main reason for reduced wellbore productivity.Experimental results show that the liner performance is significantly affected by the normal stress buildup on the liner. Experimental observations indicate sand-pack compaction due to the increase of effective stress around the liner leads to a lower porosity and permeability. The situation near the liner is further complicated by the fines accumulation that results in pore plugging and further permeability reduction. When it comes to sanding, however, higher stresses help stabilize the sand bridges behind the slots, leading to less sand production.As for the design criteria, the lower and upper bounds of the slot size are governed by plugging and sand production, respectively. Considering the stress effect on plugging and sanding, testing data indicate that both the lower and upper bounds should be revised to larger slot aperture sizes.

Improved Monitoring System for Heavy-Oil Steam-Assisted-Gravity-Drainage Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 187441, “Improved Monitoring System for Heavy-Oil Steam-Assisted-Gravity-Drainage Wells,” by Christopher Baldwin, Weatherford, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 8–11 October. The paper has not been peer reviewed. The complete paper provides an overview of the development of fiber-optic sensing for steam-assisted-gravity-drainage (SAGD) applications, including a review of more than 10 years of work in development and field applications in western Canada. Information provided in this paper is applicable beyond SAGD applications. The fiber-optic monitoring systems might also be used for intelligent, subsea, and unconventional wells. Introduction One area that has benefited from the unique advantages of fiber-optic sensing is thermal monitoring of SAGD wells. One particular fiber-optic technology that has proved successful in these thermal-monitoring applications is wavelength-domain multiplexing of Bragg-grating-based fiber-optic sensors. Commonly referred to as array temperature sensing (ATS), the Bragg-grating arrays can be manufactured splice-free for long-term reliability. The number of thermal sensing points can range from a few to well over 100 for a single cable. Each Bragg-grating sensing point provides a real-time, accurate measurement of temperature at that location along the wellbore. ATS systems have been used successfully to monitor the steam-injection and production processes in SAGD wells. ATS systems are capable of performing more-accurate temperature measurements and are able to resolve much smaller temperature features compared with distributed temperature sensing (DTS). Bragg-grating optical sensors not only provide temperature measurements but also can be packaged in a transducer to provide pressure and temperature (PT) also can be packaged in a transducer to provide pressure and temperature (PT) readings. The optical PT gauge is compatible with the surface instrumentation that records the ATS responses, allowing for the PT gauge to be integrated at the end of the ATS optical fiber for single-wellhead penetration, providing multiplexed DTS and PT measurements. Environmental Effects on Downhole Fiber-Optic Sensors The requirements for a successful monitoring system in SAGD applications are dictated by the harsh environments experienced downhole. In the past, the presence of hydrogen in these applications has caused issues with various fiber-optic sensing technologies. Improvements in optical-fiber design and downhole cable construction have helped to mitigate some of these issues, but any downhole monitoring system must be able to cope with the presence of hydrogen in relatively high-temperature environments.