Rick Chalaturnyk

MANAGEMENT OF OIL SANDS TAILINGS

ABSTRACT In Alberta, oil sands bitumen is utilized for synthetic crude oil (SCO) production by surface mining, bitumen extraction followed by primary (coking) and secondary (catalytic hydrotreating) upgrading processes. SCO is further refined in specially designed or slightly modified conventional refineries into transportation fuels. Oil sands tailings, composed of water, sands, silt, clay and residual bitumen, is produced as a byproduct of the bitumen extraction process. The tailings have poor consolidation and water release characteristics. For twenty years, significant research has been performed to improve the consolidation and water release characteristics of the tailings. Several processes were developed for the management of oil sands tailings, resulting in different recovered water characteristics, consolidation rates and consolidated solid characteristics. These processes may affect the performance of the overall plant operations. Apex Engineering Inc. (AEI) has been developing a process for the same purpose. In this process oil sands tailings are treated with Ca(OH)2 lime and CO2 and thickened using a suitable thickener. The combination of chemical treatment and the use of a thickener results in the release of process water in short retention times without accumulation of any ions in the recovered water. This makes it possible to recycle the recovered water, probably after a chemical treatment, as warm as possible, which improves the thermal efficiency of the extraction process. The AEI Process can be applied in many different fashions for the management of different fractions of the tailings effluent, depending on the overall plant operating priorities.

Numerical Simulation of Stress and Strain Due to Gas Sorption/Desorption and Their Effects on In Situ Permeability of Coalbeds

Most past studies on coal shrinkage/swelling due to gas adsorption/desorption were based on experiments under no constraint conditions. In this paper, the changes of stress and strain measured on one coal specimen under uniaxial compression in a vacuum and under axial constraint conditions during CO 2 adsorption are presented and numerically simulated. The simulation results show that a linear elastic deformation model, suitable to isotropic continuum media but widely assumed in analytical permeability models, cannot adequately simulate the deformation behaviour of coal mass even under uniaxial compression in a vacuum. The equivalent continuum medium (ECC) model considering the discontinuities of coal mass is successfully applied to simulate the deformation behaviour of the specimen for the uniaxial compression case and the axial constraint case before the occurrence of shear failure in the specimen. A detailed review of the analytical permeability models is presented and their limitations in application are discussed in this paper. The permeability, in situ stress, and production simulated with two representative analytical permeability models are compared with those calculated using the discontinuum medium coupled (DMC) permeability model and the coupled simulation. The results indicate that the DMC model provides better estimates of permeability and production than the analytical permeability models because it considers the influence of many factors such as the discontinuities and anisotropies that are ignored in analytical permeability models.

Sensitivity Study of Coalbed Methane Production With Reservoir and Geomechanic Coupling Simulation

Permeability of coal seams is one of the key factors for the success of coalbed methane (CBM) developments. It is dominated by cleat permeability in coal, which is very sensitive to the change of effective stresses. The coal matrix shrinkage due to methane production also influences cleat permeability. Using an explicit-coupling simulation method, which simultaneously simulates multiphase fluid flow and coal deformation, and a coupling permeability model, which considers the effects of the effective stress change and coal matrix shrinkage on cleat permeability, the sensitivity of CBM production to ten engineering, geologic, and coal intrinsic parameters such as cleat permeability, cleat spacing, well control area, depth, and methane content, etc., were studied in this paper. These parameters are stress and matrix shrinkage related parameters or have significantly influences on CBM production identified from previous studies. The production rate and final gas recovery from conventional simulations and coupling simulations are also compared. Of the parameters studied, permeability, cleat spacing, and in situ stresses were found to be the most sensitive parameters that influence CBM production. Medium sensitivity was found for the coefficient of matrix shrinkage, the Langmuir volume, pressure gradient, and well control area, while the least sensitive parameters included Poissons ratio, Youngs modulus, and the Langmuir pressure.

A Mathematical Improvement to SAGD Using Geomechanical Modelling

Steam assisted gravity drainage (SAGD) is a thermal oil recovery technique which has been used mostly for Albertas unconventional oil sands reservoirs. Roger Butler, known as the father of SAGD, was the first one to establish a theory and an analytical model for SAGD. His model is a rigorous solution and is widely referred to as a SAGD fast flow simulator. However, geomechanics, which has been shown to be a relevant part of SAGDs physics, has not been included in the model. When rock properties are influenced by geomechanical behaviour, the Butler theory is not able to capture the complete physics of the SAGD process. In such cases, the model must adopt unrealistic or high values for rock properties. In this study, a classical theory in the field of geotechnical engineering (limit equilibrium) is employed to act as the geomechanical module for SAGDs mathematical coupled simulation. The Butler/Reis model has also been improved using a model of slices for flow simulation. Methodology of combining these two models in a single coupled mathematical simulator is presented in this paper. The solver is a fast and realistic proxy and can be used as a low-order tool for history matching. The results of coupled simulations show that the model is able to predict permeability and porosity of the reservoir closer to real values than uncoupled (flow only) modelling.

History Match of the UTF Phase A Project with Coupled Reservoir Geomechanical Simulation

Field operation of the Underground Test Facility (UTF) Phase A SAGD project started in November 1987 and terminated in October 1990. In order to understand the interactions between fluid flow and geomechanical behaviour of the reservoir during the SAGD operation, the coupled reservoir geomechanical simulation methodology was applied to history match the measured performance of the project. Reservoir and geomechanical responses were available from an extensive instrumentation program designed for this project. Reservoir pressure, temperature, horizontal displacement, vertical strain and volumetric strain from the coupled simulation were compared with the data obtained from the field survey. These comparisons show that the coupled reservoir geomechanical simulation methodology has the potential to capture both reservoir and geomechanical responses during SAGD. In addition, the steam chamber propagation modes, both in the field and in the simulation, were also discussed.

When Is It Important to Consider Geomechanics in SAGD Operations

This paper generalizes the typical reservoir conditions for which SAGD is being implemented or considered in order to parametrically analyze the influence of geomechanical factors on the startup and production phases of SAGD projects. Numerical simulation of the SAGD process using a thermal reservoir program and a geomechanical program is used to assess the relative influence geomechanics may have on SAGD operations. While variations to the initial dual well SAGD process are becoming numerous, this study presents analysis results for only dual well SAGD geometries. A primary focus of this research is to clearly define the role of pore volume change (compressibility or shear-induced) on the basis of fundamental geomechanical parameters and correct an ongoing misconception that formation dilation can be simulated based on injection pressure alone. Dilation is a complicated process controlled by significantly more parameters than just injection pressure. Clear, definable guidelines are presented to aid SAGD project designers in determining the relative importance of the geomechanical response of their particular reservoir. The major geomechanical/reservoir factors studied include: 1) initial in situ effective stress state; 2) initial pore pressure; 3) steam injection pressure and temperature; and, 4) process geometry variables, such as well spacing and wellpair spacing.

Permeability variations associated with shearing and isotropic unloading during the SAGD process

This paper discusses the variations of reservoir permeability within uneonsolidatcd sands due to isotropic and devialoric (shear) processes during the SAGD process. Isotropic unloading results from the steam inspection pressure, which is generally higher than the initial reservoir pressure. The high steam injection pressure results in the increase of pore pressure and reduces the confining effective stress within the drained zone and part of the partially drained zone. The shearing process is induced primarily by changes in total stress but can also occur with increased pore pressures. High steam temperatures associated with the SAGD process result in significant volumetric expansion of the reservoir material within the steam chandler. Thus, total stress is increased and the shearing process may occur beyond the steam chamber surface. Both the isotropic unloading and shearing processes can induce reservoir permeability variation because of the change in pore space, pore shape, and pore throat. For isotropic unloading, the configuration of the grains or their relative position is, for the most part, unchanged and the grains simply move apart without relative rearrangement. Whereas the shearing process induces substantial relative motion of the grains and significant changes in pore geometry. Based on lab test results, it is summarized that the isotropic unloading process produces much smaller changes in volume, absolute permeability, and water effective permeability compared to the shearing process. Consequently, incorporating stress-induced permeability change within coupled reservoir gcorneehanical simulations requires different relationships or models for these two conditions. In addition, some empirical permeability relationships, such as the Kozeny-Cannan model, Tortikes equation, and Chardabellass terms, arc also discussed.

Geological storage of CO2: Time frames, monitoring and verification

Publisher Summary This chapter explores that the scope, frequency, duration, and results of monitoring programs combined with interpretation of the monitoring results forms the key components of a monitored decision approach for verifying the integrity of a geological storage project. Monitoring provides the confidence that the CO 2 has been injected and stored in an environmentally sound and safe manner and provides the necessary accounting metrics for emissions trading scenarios based on geological storage. A monitored decision framework recognizes uncertainties in the geological storage system and allows design decisions to be made with the knowledge that planned long-term observations and their interpretation will provide information to decrease the uncertainties, as well as providing contingencies for all envisioned outcomes of the monitoring program. However, long-term monitoring requires integration with a “working hypothesis” of the storage mechanisms.

Issues With Reservoir Geomechanical Simulations of the SAGD Process

In the SAGD process, steam injection may result in pore pressure changes around the steam chamber in the reservoir. The magnitude of the pore pressure change depends on the steam injection pressure and the relative position of the steam chamber within the reservoir. Injected steam also increases the temperature within and adjacent to the steam chamber and thus introduces thermal expansion effects. The complex interaction of pore pressure and temperature throughout the reservoir result in varying degrees of reservoir geomechanical interactions that must be considered when contemplating reservoir geomechanical simulations of the SAGD process. The primary geomechanical influence on SAGD recovery is associated with the volume change of the sand matrix in response to effective stress changes induced by steam injection pressures and temperatures. Reservoir parameters and processes, such as compressibility, porosity (pore volume), absolute permeability, relative permeability, saturations, capillary pressure, enthalpy transmissibility, gas evolution, and thermal expansion effects, are all affected by bulk volume changes. In this paper, variations of these parameters due to geomechanical effect are analyzed and discussed based on related test results, calculation, and simulation. Their impacts on reservoir geomechanical simulations of the SAGD process are discussed.

Sequentially coupled flow-geomechanical modeling of underground coal gasification for a three-dimensional problem

Underground coal gasification (UCG) has been identified as an environmentally friendly technique for gasification of deep un-mineable coal seams in situ. This technology has the potential to be a clean and promising energy provider from coal seams with minimal greenhouse gas emission. The UCG eliminates the presence of coal miners underground hence, it is believed to be a much safer technique compared to the deep coal mining method. The UCG includes drilling injection and production wells into the coal seam, igniting coal, and injecting oxygen-based mix to facilitate coal gasification. Produced syngas is extracted from the production well. Evolution of a cavity created from the gasification process along with high temperature as well as change in pore fluid pressure causes mechanical changes to the coal and surrounding formations. Therefore, simulation of the gasification process alone is not sufficient to represent this complex thermal-hydro-chemical–mechanical process. Instead, a coupled flow and geomechanical modeling can help better represent the process by allowing simultaneous observation of the syngas production, advancement of the gasification chamber, and the cavity growth. Adaptation of such a coupled simulation would aid in optimization of the UCG process while helping controlling and mitigating the environmental risks caused by geomechanical failure and syngas loss to the groundwater. This paper presents results of a sequentially coupled flow-geomechanical simulation of a three-dimensional (3D) UCG example using the numerical methodology devised in this study. The 3D model includes caprock on top, coal seam in the middle, and another layer of rock underneath. Gasification modeling was conducted in the Computer Modelling Group Ltd. (CMG)’s Steam, Thermal, and Advanced processes Reservoir Simulator (STARS). Temperature and fluid pressure of each grid block as well as the cavity geometry, at the timestep level, were passed from the STARS to the geomechanical simulator i.e. the Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) computer program (from the Itasca Consulting Group Inc.). Key features of the UCG process which were investigated herein include syngas flow rate, cavity growth, temperature and pressure profiles, porosity and permeability changes, and stress and deformation in coal and rock layers. It was observed that the coal matrix deformed towards the cavity, displacement and additional stress happened, and some blocks in the coal and rock layers mechanically failed.