Authors: Lei Li, Carlos F Lange, Yongsheng Ma
Computational fluid dynamics has been extensively used for fluid flow simulation and thus guiding the flow control device design. However, computational fluid dynamics simulation requires explicit geometry input and complicated solver setup, which is a barrier in case of the cyclic computer-aided design/computational fluid dynamics integrated design process. Tedious human interventions are inevitable to make up the gap. To fix this issue, this work proposed a theoretical framework where the computational fluid dynamics solver setup can be intelligently assisted by the simulation intent capture. Two feature concepts, the fluid physics feature and the dynamic physics feature, have been defined to support the simulation intent capture. A prototype has been developed for the computer-aided design/computational fluid dynamics integrated design implementation without the need of human intervention, where the design intent and computational fluid dynamics simulation intent are associated seamlessly. An outflow control device used in the steam-assisted gravity drainage process is studied using this prototype, and the target performance of the device is effectively optimized.
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Authors: Da Zhu (RGL Reservoir Management Inc.) | Ian D. Gates (University of Calgary)
Given the high viscosity of the oil, bitumen from oil sands reservoirs in western Canada is recovered by using steam which, due to its temperature, lowers its viscosity. One of the key issues faced by the operators is the steam conformance of the depletion chamber around wells. The greater the fingering phenomena of steam at the edge of chamber, the worse is the chamber uniformity and utilization of the well, and the greater are the green house gas emissions and water use per unit oil recovered. Fingering has long been explained as the penetration of steam phase into the oil phase which arises from an unfavourable mobility ratio. In this paper, we introduce linear instability analyses (Orr-Sommerfeld and Rayleigh-Taylor/Saffman-Taylor instability) of the interface between steam and oil layers and conduct a series of numerical simulations to reveal that fingering in the steam-assisted heavy oil recovery at the top of the steam chamber is created due to solution gas exsolution whereas fingering at the chamber edge is due to viscous shear instability. The results show that non-ideal steam conformance is inevitable even in homogeneous reservoirs.
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Authors: Marty Lastiwka (Suncor Energy) | Chris Bailey (Suncor Energy) | Bruce James (Suncor Energy) | Da Zhu (RGL Reservoir Management)
Over the past few years, an increasing number of operators in steam assisted gravity drainage (SAGD) in situ recovery of bitumen in the Alberta Oil Sands are becoming interested in the use of flow control devices (FCDs). Initial field trials by some operators of these devices have shown promise in improving steam chamber conformance, reducing incidences of steam breakthrough, high vapour production, and in addressing liner reliability concerns related to steam jetting.
While the application of FCDs is well-established in the conventional oil and gas industry to control gas and water coning, there are still a number of questions on how to implement FCDs optimally in SAGD. One major difference in the application of FCDs in SAGD compared to the conventional oil and gas industry is the high temperature environment with steam and elevated erosion risk.
The purpose of this paper is to present some practical considerations for the selection of FCDs and optimal completion FCD design for SAGD applications. In the first section, a discussion is presented on how to compare the performance of different flow control devices. Most devices have not been tested for SAGD, and there is a need for more comprehensive testing. The focus of the second section is on practical considerations for the installation of FCDs in a SAGD injection and production wells.
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Authors: Vahidoddin Fattahpour (University of Alberta) | Vittor Maciel (University of Alberta) | Mahdi Mahmoudi (University of Alberta) | Ken Chen (University of Alberta) | Alireza Nouri (University of Alberta) | Michael Leitch (RGL Reservoir Management)
There is a growing interest in physical model testing of the reservoir and large-scale sand control testing for oil sands. These experiments require the synthesization of representative sand-packs. Particle size distributions (PSDs) of these sand-packs ought to be comparable to the PSD of target oil sands. For practical and economic reasons, it is favorable to test samples with a limited number of PSDs, yet representative of a spectrum of oil sands. The aim of this paper is to categorize the PSD of Alberta oil sands to a limited but representative number for use in laboratory research.
This paper is based on the analysis of 152 PSD curves for Alberta oil sands. To categorize these PSD’s in a meaningful way, an algorithmic approach is presented which uses attributes that are widely used in sand control design (e.g. D10, D50, D70, fines content) and, subsequently screens and sorts the data to produce a finite number of PSD categories which represent the majority of the data. Rules are implemented in the algorithm to limit the number of categories (≤7), and require that each category cover a significant subset of the total data (≥10%).
A review of the published PSDs for oil sands across Alberta indicates a significant variation in the PSD curves even within the same reservoir. However, in spite of the fact that PSD data show a large variation, PSD categories can be identified to build representative oil sand samples for design and testing purposes. For the database used in this investigation, four major and two minor PSD classes were identified. These six PSD classes, cover more than 87% of the analyzed PSDs. Introduced classes and existing PSD classifications in the literature share interesting similarities. However, certain differences, such as the lack of very coarse ranges (D50~500 µm) was observed.
The method which is introduced for oil sand classification is based on the D-values which are commonly used in screen aperture design. This method provides a useful tool for both screen designers and researchers to categorize and focus their work on a specific set of representative PSDs, rather than a wide distribution of PSDs.
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Authors: Mahdi Mahmoudi (University of Alberta) | Vahidoddin Fattahpour (University of Alberta) | Alireza Nouri (University of Alberta) | Michael Leitch (RGL Reservoir Management)
This paper presents the results of an experimental investigation to determine the mechanisms of pore plugging and permeability reduction near SAGD screen liners. The aim is to arrive at a liner design that maximizes wellbore productivity without compromising the sand control function of the liner.
We set up a large-scale Sand Retention Testing (SRT) facility that accommodates a multi-slot liner coupon at the base of a sand-pack with representative grain shape and particle size distribution (PSD) of typical oil sands. Brine is injected at different flow rates and pressure differences across the coupon and the sand-pack as well as the mass and PSD of the produced sand and fines are measured during the test. Further, the PSD and concentration of migrated fines (<44 microns) along the sand-pack are determined in a post-mortem analysis. The testing results are used to assess the effect of slot size and slot density on the sand control performance as well as pore-plugging and permeability alterations near the sand-control liner.
We observed that the slot size, slot density and flow rate highly affect the concentration and PSD of produced fines as well as accumulated fines (pore clogging) above the screen. For the same flow rates and total injected pore volume, wider screen aperture and higher slot density result in lower fines accumulation above the screen but more sanding. Further, the variation of slot density alters the flow convergence behind the slots, hence, the size and concentration of mobilized fines. Results indicate that higher fines concentration near the screen reduces the retained permeability, hence, lowers the wellbore productivity.
This paper provides a new insight into pore plugging and fines migration adjacent the sand control liner. It also introduces a new testing method to optimize the design of sand control liners for minimum productivity impairment in SAGD projects.
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Authors: Mahdi Mahmoudi (University of Alberta) | Vahidoddin Fattahpour (University of Alberta) | Alireza Nouri (University of Alberta) | Ting Yao (the University of Hong Kong) | Beatrice Anne Baudet (the University of Hong Kong) | Michael Leitch (RGL Reservoir Management Inc.) | Brent Fermaniuk (RGL Reservoir Management Inc.)
This paper presents the results of several large-scale Sand Retention Tests (SRTs), which are used to test and refine the criteria used for slotted liner design. The paper also presents the analysis of test measurements to improve the understanding of the parameters that influence the sand control performance. The parameters include Particle Size Distribution (PSD), flow rate, slot opening size and slot density.
The SRT facility was commissioned to improve the existing testing methods by (1) using multiple-slot rather than single-slot coupons, (2) using more realistic sand pack preparation/saturation procedures than the existing practices, (3) measuring the pressure drop along the sand pack and across the liner coupon to assess the retained permeability and flow convergence, and (4) post-mortem analysis of the sand pack to measure fines/clay content along the sand pack as a direct measure of fines migration. Several tests were performed by varying the slot size, slot density, and PSD of the sand pack, and flow rate. The testing data were used to validate and improve the current industrial design of slotted liners.
Test measurements and observations indicate that the sand pack preparation procedure highly affects the testing results. For typical field porosities and PSDs, we observed finite amount of sand production bellow the existing criteria for sanding during the SRT, for the screens designed based on existing models. Testing data also indicate smaller retained permeability for lower slot density due to converging flow. Moreover, measurements indicate lower retained permeability for narrower slot width, caused by the accumulation of fines and pore plugging in the liner’s vicinity. However, larger slot width than a certain size contributes to higher levels of sanding. Three different sanding modes are identified: (1) initial sanding or sand occurrence, (2) flow rate dependent transient and (3) flow rate dependent continuous sanding. It is proposed that the sanding mode should be also included in the design criteria along with the acceptable sanding threshold. Test results indicate the combined effect of the slot size and density on both retained permeability and sand production. These findings lead to a new design approach for maximum retained permeability and acceptable sand retention.
This paper introduces a new set of design criteria for slotted liners based on the results of a novel large-scale testing to evaluate the sand control for thermal heavy oil production applications. Also it provides a better understanding of the sand production and the role of the slot width and slot density on the sand production. The paper also presents an improved understanding of the sanding and permeability evolution close to the liner in relation to several liners and flow parameters. The set-up, testing procedures, and measurement methods that are used in the experiments improve the existing methods in several fronts.
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Authors: Vahidoddin Fattahpour (University of Alberta) | Saman Azadbakht (University of Alberta) | Mahdi Mahmoudi (University of Alberta) | Yujia Guo (University of Alberta) | Alireza Nouri (University of Alberta) | Michael Leitch (RGL Reservoir Management Inc.)
In SAGD wells, the gap between the oil sand and the sand control liner closes or collapses over time due to such factors as the oil sand thermal expansion, the melting of bitumen and the ensuing loss of the apparent bonding between the grains. The result is the buildup of effective stresses and the gradual compaction of the oil sands around the liner. Current practices for the sand control design do not account for the effect of time-dependent effective stress variation around the liner on the sand control performance. In this paper, we outline the results of an experimental study on the effect of near-liner effective stress on the performance of slotted liners.
This study builds on existing experimental procedures and investigates fines migration, sand production and clogging tendency of slotted liner coupons in large-scale unconsolidated sand-packs. Sand-packs with controlled properties (grain size distribution, grain shape, and mineralogy) are packed on a multi-slot sand control coupon in a triaxial cell assembly. Varying levels of stress are applied to the sand-packs in directions parallel and perpendicular to the multi-slot coupon. For each stress level, brine is injected into the sand-pack from the top surface of the sample towards the coupon. Test measurements include pressure drops across the sand-pack and the coupon as well as the produced sand/fines mass for each stress level. Post-mortem analysis is performed to measure fines/clay concentration along the sand-pack as a direct measure of fines migration.
Experimental results show that under the subsequent increase in effective stresses, sand-packs experience considerable deformations in directions parallel and perpendicular to the multi-slot coupon; which result in a drastic drop in the porosity and retained permeability. Test results show that the maximum reduction in permeability occurs in the vicinity of the multi-slot coupons due to the fines accumulation and the higher compaction in that region. In comparison to experiments with no confining stress, the application of confining stress results in lower retained permeability in the sand-packs as well as reduced sand production.
This paper presents, for the first time, the effect of near wellbore effective stress on clogging tendency and sand retention characteristics of slotted liner completions. The tests allow the assessment of the adequacy of the use of existing design criteria over the life cycle of the well under variable stress conditions around the liner.
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Authors: Mahdi Mahmoudi (University of Alberta) | Vahidoddin Fattahpour (University of Alberta) | Alireza Nouri (University of Alberta) | Saad Rasoul (University of Alberta) | Ting Yao (The University of Hong Kong) | Beatrice Anne Baudet (The University of Hong Kong) | Michael Leitch (RGL Reservoir Management Inc.) | Mohammad Soroush (University of Trinidad and Tobago)
This paper presents the characterization of oil sands from the McMurray Formation. The main objective of this paper is to investigate the possibility of replicating the oil sands by the mixtures of commercial sands and fines for large-scale testing. There is a growing interest in large-scale evaluation testing for sand control devices that require considerable amounts of representative oil sands materials. However, natural representative oil sands samples are usually not available or are limited in quantity. Therefore, replicating the oil sands is essential for such tests.
Twenty-three oil sands samples were collected from two wells in the McMurray Formation and cleaned using the Soxhlet extraction technique. The cleaned samples were examined using the image analysis technique and Scanning Electron Microscope (SEM) imaging to study their Particle Size Distribution (PSD), shape factors, mineralogy, and texture. Similar analysis was performed on eleven series of commercial sands to compare their shape, mineralogy, and texture with those of oil sands. Particle Size Distribution of 10 commercial fines was also analyzed with a particle sizer to cover the required fine/clay part of the duplicated samples. Direct shear and 1D consolidation were performed to compare the mechanical properties of the oil sands samples and the duplicated mixtures of commercial sands and fines.
The shape factors of the oil sand and the selected commercial sand samples are in close agreement. In addition to the common average/cumulative shape factor measurements, this paper also presents the variation of shape factors within each sample for different grain sizes. The results show the same sand shape characteristics among all oil sand samples as well as the tested commercial sands. Further, XRD results indicate a similar mineralogy for the commercial sands and the oil sands samples. The SEM images show random changes in the surface texture of both oil sands and commercial sands with no observable trends. We were able to use commercial sands and fines mixture with similar grain shape properties to duplicate the PSD of the oil sand samples. Direct shear and 1D consolidation testing of the oil sands and samples made of commercial sands and fines show similar consolidation and frictional properties for both the duplicated mixture and cleaned oil sands for the same compaction level (porosities).
This paper provides a procedure for duplicating the oil sands with commercial sands and fines. It also provides detailed information on the mineralogy, texture, and the variation of the shape characteristics for oil sands from the McMurray Formation.
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Authors: Fattahpour, Vahidoddin & Mahmoudi, Mahdi & Nouri, Alireza & Leitch, Michael.
Several sand control techniques have been used in SAGD wells in Western Canada. For most projects, slotted liner has been the sand control of choice for its economics, ease of use, and acceptable performance. Careful design of the slot geometry is crucial to maintain long term wellbore performance but is not an easy task in formations with high fines content and other challenging characteristics, such as in Grand Rapids or shore-face at the upper member of McMurray. The objective in the design of sand control is generally to minimize the production of sand and maximize the retained permeability in the liner’s vicinity by allowing the production of any mobilized fines, avoiding extreme pressure drops by minimizing the curvature of flow streamlines around the slots, and avoiding the plugging of slots over time. Design practices for sand control in SAGD wells are currently based mostly on Particle Size Distribution (PSD) and the fines (<44um) content. Where designers focus principally on retaining sand rather than maximizing the retained permeability in the liner’s vicinity, there is an increased risk of underperforming completion designs, but long term well performance requires a reasonable tolerance for solids production. This paper provides a critical review of existing design criteria and the experimental testing and techniques for assessing the sand control design for SAGD production wells. It reviews the mechanisms which cause sand production and fines migration in relation to the PSD of oil sands and the formation clay and silt content. In addition, the paper presents field failure cases from the literature and examines the common problems with different types of sand control. Finally, practical recommendations are presented to further improve the current design criteria and sand control experiments to achieve higher productivity index, lower skin buildup, and greater durability of sand control screens.
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Authors: Mahdi Mahmoudi, University of Alberta; Vahidoddin Fattahpour, University of Alberta; Alireza Nouri, University of Alberta; Saad Rasool, University of Alberta; Michael Leitch, RGL Reservoir Management Inc.
The quantification of fines migration in the vicinity of sand control screens in SAGD wells is of paramount importance to operating companies, who require the wells to operate under optimum conditions for a period of 10-15 years. Fines migration can lead to the plugging of pore spaces around the liner and result in reduced permeability in the liner’s vicinity, hence, lowering the wellbore productivity. This paper investigates the fines migration in relation to slot width and density in SAGD wells. A series of laboratory experiments was performed by using a Sand Retention Testing (SRT) facility which accommodates a sand pack sample and a multi-slot coupon to represent the near-wellbore high-porosity zone and sand control liner, respectively. As fluid was pumped through the sand pack and across the slotted coupon, the pressure drop across the sand pack and coupon was measured, along with the mass and Particle Size Distribution (PSD) of produced fines and sand. After the flow test, the sand pack was dissected, and the PSD of fines portion of sand pack was measured to assess the movement and concentration of fines over the course of the test. Test observations indicate that the slot width, slot density, and the flow rate highly affect the fines migration/production and the PSD of the migrated and produced fines. Larger slot widths increase the mass of the produced and migrated fines. Further observations indicate that the mass and size of produced fines is highly dependent on the flow rate and that there is a critical rate below which little amounts of fines are produced or move in the porous medium.
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