Electrical Heating Methods for Oil Reservoir Stimulation

Increased demand to produce oil from unconventional resources and a heightened focus on environmental stewardship are driving the energy industry to find novel ways to increase production from oil fields.  Three dimensional engineering simulations are helping energy companies evaluate new concepts and verify every design.  In this article, use of 3D simulation demonstrates electromagnetic heating in oil sands as a potential bitumen mobilization and extraction method.

Historically, reservoir modeling software has been the primary tool used to predict oil flow in conventional oil fields. As resources become more limited, and terrain more unpredictable, oil companies are exploring innovative ways to improve oil extraction from existing fields. With increasing challenges in drilling and production from unconventional resources, high-fidelity, 3D engineering software tools are used for detailed analysis of equipment and concept evaluation to produce oil and gas with less energy, less water input, and with a strong focus on reducing environmental impact.

One concept that has been realized with 3D simulation is the electromagnetic/radio frequency (RF) heating in oil sands for the mobilization of heavy bitumen to increase oil production. Oil in older, shallow reservoirs can consist of crude oil that is heavy and viscous – making the valuable oil quite difficult to extract. Simulation helps companies evaluate existing oil fields and develop the most efficient means to bring these new methods of bitumen extraction to market faster and more reliably.

These software programs are science-based and complement conventional prototyping and laboratory and field testing. Engineering simulation methods solve the fundamental mathematical equations related to fluid mechanics, structural mechanics, electromagnetics, acoustics and chemical reactions – all critical components that oil engineers need to fully understand the optimum extraction plan before they begin drilling.  In addition, the technology is applied to studies of mass, momentum and heat transfer, as well as analysis of stress, fracture, vibration, temperature, flow distribution, erosion, low- and high-frequency electromagnetic fields, multiphase and rock mechanics, among others. This knowledge often provides critical insight that enables engineers to test their design and concepts in a virtual environment. The appropriate simulation framework can explore a single type of physics, or multi-physics can handle multi-scale and multi-domain problems. While the software programs are relatively easy to use, the underlying technology is comprehensive with decades of validation based refinements made to the simulation methodologies.

The following are sample results from three different and unrelated simulations used to highlight structural analysis, fluid mechanics performance and electromagnetic field calculations.

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Figure 1. Sample post-processing results from 3-D engineering simulation analysis from left to right: a) Structural analysis contour plots of deformation on a tank subjected to a seismic event; b) Contour plots of pressure on a pump blades in an engineering fluid dynamics (CFD) simulation c) Contours of the magnetic field magnitude for a particular current excitation distribution inside of an offshore umbilical cable.

Application of engineering simulation to electric heating of oil sand

Two primary methods are commonly used for oil sands oil extraction. The first method is open pit mining (OPM), in which oil sands are mined and transported to a processing plant to extract the bitumen from the oil sand. The second method, called steam assisted gravity drainage (SAGD), leaves the oil sand in place (in-situ). In this process, high pressure steam is continuously injected using an injector well to heat the oil and reduce its viscosity. This causes the oil to drain to a lower production well, where it can be pumped and further processed, upgraded and transported as crude. Both of these methods can be energy and water intensive, generally expensive, and perceived to have a broader emission and environmental impact than conventional oil and gas production.

Industry motivation is to reduce energy use and to develop technologies that use less water, while simultaneously reducing capital expenses of steam generation, water treatment and recycling facilities.  To heat the oil in-situ, the industry is considering promising ideas to heat the oil using electromagnetic heating processes. The ideas are to transfer energy directly into oil reservoirs through underground emitters of high frequency electromagnetic fields (KHz to low MHz range) and/or by transmitting low frequency electric current through buried heating electrodes. In conjunction with the electromagnetic field sources, fluids that are known to be electromagnetic absorbers may also be injected into the extraction site since bitumen itself does not absorb electromagnetic field energy well.  Degrees of freedom for optimizing this process include choosing the right geometry of the field energy applicators, and the frequencies in the high frequency case, or phases in the low frequency case to optimize field interaction with the reservoir conditions over the extraction time period. The ultimate goal is to heat and reduce the bitumen viscosity and extract the oil. (Journal of Petroleum Technology, Sept. 2012)

Three dimensional simulations involving a combination of electromagnetic, thermal, structural and fluids analysis can be used to evaluate, design and optimize the effectiveness of  these and other novel methods under consideration by industry. The simulations involving electromagnetic heating also must account for model changes in viscosity, oil mobility, and distribution of solvents or other chemicals used to increase reservoir electrical conductivity. In the real world, reservoir complexities include variations in soil/rock/bitumen properties, spatial moisture profiles and injected solvent placement and distribution. This information is translated into a virtual model comprised of the appropriate spatial electrical material properties such as dielectric permittivity, loss tangent, and/or electrical conductivity.  Magnetic material properties may also be included if present in underground material such as nickel, although these are less common.  Once material properties are supplied, the electromagnetic field source representation is created via 3D CAD.  The electric and magnetic fields are calculated in the 3D volume according to Maxwell’s equations. Related calculations such as surface and volume loss densities characterize the spatial electromagnetic power dissipation, which is may be visualized to quickly understand field penetration depth and heat source distribution. The electromagnetic loss densities are passed to thermal/fluids analysis software to calculate heating with purely thermal boundary conditions, or to calculate heating with both thermal and fluid effects.

The virtual prototyping methodology that utilizes electromagnetic field calculations in software is used in a variety of other industries. On the frequency side, some examples include modeling of electric machines, motors, actuators, solenoids, magnetic circuits, alternators, transformers, etc.  High frequency modeling applications full-wave electromagnetic field simulation of antennas, data transmission in computers and networking equipment, RF signal path modeling, biomedical devices, MRI safety, cell phones and tablets, electromagnetic shielding, emissions, interference, radar systems and many others.

Figure 2 and 3, illustrates sample results of from an electromagnetic simulation showing electric and temperature fields.    

Figure 2. Electric field coupling on a cut plane for a 1.5GHz interdigital bandpass filter.

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Figure 3a. Electric field distribution at 2MHz for an “RF plus critical fluid extraction” model

Figure 3b. Temperature gradients as a result of the electromagnetic source applied

The advances in computational technology and the capabilities in the integrated engineering simulation software make solving a broad range of industrial applications possible on a typical engineering computer/workstation. Engineering simulation tools with appropriate physical modeling capabilities and when used properly enables designers, engineers and researchers to advance their knowledge and develop insight into their design, processes and technology concepts for many applications including drilling, production, transport, refining and processing of oil and gas.  Whether for improvement of established processes or for developing the concepts and products of the future, engineers are now able to leverage simulation based product development to produce higher-quality, better-performing, products and processes that can have a profound impact on energy production.