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.
Download paper
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.
Download paper
Authors: Lei Li, C. F. Lange, Yongsheng Ma
Multi-view feature modelling provides a specific view for each phase in product development. The analysis view should be fully integrated with CAD models in a multi-view product development environment for simulation-based design. In the development of fluid flow products, CFD (Computational Fluid Dynamics) is increasingly used as an advanced support. However, the successful application of CFD requires special knowledge and rich experience, which is a barrier for the conversion from the design view to the analysis view, and the maintenance of information consistency. Several approaches to multiple feature views have been proposed, such as design by features, feature recognition and feature conversion. In one-way feature conversion, features in a specific view are usually derived from the original design view. Bronsvoort and Noort put forward a multiple-way approach which enables a designer to modify the product model from an arbitrary view. In this paper, the CAE interface protocol is used to convert the features in the design view into the CAE boundary features [5] in the analysis view. Based on the physical knowledge, an expert system is established to further process those features and generate a robust simulation model with the help of fluid physics features and dynamic physics features in the analysis view.
Download paper
Authors: Matthew Miersma
One of the main methods of extracting oil from deep oil sands deposits is through the use of steam assisted gravity drainage (SAGD). For the best performance, inflow control devices (ICDs) are implemented along the SAGD production well to even out production and restrict unwanted fluids. Current methods of evaluating these devices rely on criteria that are dependent on the flow rate and fluid properties at which they are measured. In this study, three new criteria are proposed to evaluate and compare ICDs. These new criteria are derived from the physics of the flow in order to tie them to specific aspects of the flow and to have a reduced dependence on the flow rate and fluid properties. To further reduce the dependence of the criteria, they are calculated from a range of data, using a least squares fit. In order to evaluate the proposed criteria, detailed CFD models are developed for six fundamental ICD designs: a 15◦ nozzle, a 40◦ nozzle, a long channel, an expanding nozzle, a device based on Tesla’s fluidic diode, and a vortex based device. The CFD models are carefully tested to ensure they accurately model the flow. Using these simulations, the three criteria are calculated for each device. The criteria are then compared to the flow results and examined for flow and viscosity independence. Finally, the criteria are used to compare the six ICDs and identify the best design. The new criteria are not only better than existing criteria for comparing ICDs, but they are also specially adapted to support design development and optimization of new devices.
Download paper
Authors: Li, Lei & Ma, Yongsheng & Lange, Carlos
The complexity in configuring the CFD solver imposes a barrier for users to efficiently setup the solver and obtain satisfactory results. Such kind of deficiency becomes more obvious when it comes to simulation-based design where the CFD solver is expected to respond to design changes automatically. By applying artificial intelligence, expert systems can be used to capture the knowledge involved in CFD simulation and then assist the solver configuration. This paper proposes an expert system for both dry and wet steam simulation. According to the product design, the expert system is able to select the right module to model the steam flow. Based on the derived non-dimensional numbers, appropriate physics models can be selected to run the simulation. Grid adaption, higher order schemes, and a subroutine for advanced turbulence models help to improve the accuracy of the CFD model after rounds of simulation. The output of the expert system is a robust simulation model with accurate results which are guaranteed by flow regime validation, grid independence analysis, and error estimation. The effectiveness of the proposed system is demonstrated by the analysis of a contracted pipe. In dry steam simulation scenario, the error induced by the expert system is smaller than that of the traditional ANSYS batch mode. The results obtained by the expert system also match well the empirical results when it comes to wet steam simulation.
Download paper
Authors: Lange, Carlos & Ma, Yongsheng.
CFD (Computational Fluid Dynamics) requires strong expertise and extensive training to obtain accurate results. To improve the usability in the complex product development process, two new types of engineering features, fluid physics feature and dynamic physics feature, which convey the simulation intent, are proposed in this paper to achieve CFD solver setup automation and robust simulation model generation in an ideal CAD/CAE integration system. Further, the association between simulation intent and design intent is integrated with another newly defined fluid functional feature in order to achieve the consistency. Consequently, an optimal design could be achieved by considering production operation, manufacturability and cost analysis concurrently. A case study of steam assisted gravity drainage (SAGD) outflow control device (OCD) is presented to show the prospective benefits of the method.
Download paper
Authors: Da Zhu (RGL Reservoir Management Inc.) | Gary Bunio (Suncor Energy) | Ian D. Gates (University of Calgary)
The main challenges faced by oil sands operators are the cost of operations and the environmental intensity of the recovery processes. The Athabasca oil sands deposit contains bitumen with viscosity typically over 1 million cP. To lower the viscosity of the bitumen so that it can be drained from these reservoirs, it is heated with injected steam by using Steam-Assisted Gravity Drainage (SAGD). This process is effective and enables recovery factors over 60%. The major cost in the recovery process is steam generation and associated water treatment and handling. The combustion of natural gas to generate steam is the main origin of the carbon dioxide emissions associated with SAGD. An alternative to steam injection is the use of solvents co-injected with steam. Solvents dilute bitumen leading to an oil phase with reduced viscosity. Also, there is potential to recycle solvent for re-injection. Thus, solvent added to steam can improve the steam-to-oil ratio and as a consequence can lower the carbon dioxide emissions per unit volume oil produced. In this extended abstract, we describe a phased solvent and heat process that yields improved performance beyond that of SAGD and current solvent-aided SAGD processes.
Download paper
Authors: Da Zhu (RGL Reservoir Management Inc.) | Jacky Wang (University of Calgary) | Yi Su (University of Calgary) | Ian D. Gates (University of Calgary)
Numerical simulators have been extensively used in reservoir engineering for several decades. These simulators, based on energy, material, and momentum (multiphase Darcy law) balances and thermodynamic equilibrium of components between phases, solve a coupled set of nonlinear partial differential equations. We have observed multiple states for simulation of Steam-Assisted Gravity Drainage (SAGD) with multiple steam-to-oil ratios resulting at the same steam injection rate. The existence of multiple solutions and potentially limit cycle behavior and its associated bifurcation branching in the operation parameter space inspires us to consider a dynamical approach to reservoir simulation. There are four dominant states of stability: absolutely stable; neutrally stable; unstable subject to infinitesimal perturbation; and unstable subject to finite amplitude perturbation. In essence, instability is a process that releases potential energy stored in the base state to the perturbation state. In a reservoir simulation, if we impose a perturbation with a certain magnitude to a quasi-steady state, linear stability theory predicts that once the system becomes unstable, the magnitude of the perturbation grows with time infinitely. However, in reality, due to nonlinearity the system causes it to evolve to a new quasi-steady state. The questions that we are going to address in this paper are: How can we use a transient reservoir simulator to detect instability of the system that may lead to different and multiple operating states? As a case study, we will use a 2D homogeneous SAGD model. Once the model reaches a quasi-steady state, we will call it our base state. Then we impose different steam injection rate perturbations on the system and see how the system responds to these changes. Different behaviors result –for finite amplitude perturbations, the state evolves to a new state (Hopf bifurcation) (Strogatz 2014). Our goal is to use an existing commercial simulator to construct multiple operating states and describe an approach to detect them. Multiple operating states could have significant implications for process control and risk/uncertainty management of reservoir operations.
Download paper
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.
Download paper
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.
Download paper
