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oil and gas modelling


Drilling down


From identifying new sources of oil, to aiding engineers in the design and construction of off-shore platforms, modelling software plays an important role within the oil and gas industry


Bruce Klimpke, technical director at Integrated Engineering Software


T


he oil and gas industry is in a continuous state of research and development as the demand for fuel increases and sources diminish. There is also a global need


for a more ‘green’ approach with a required reduction in emissions and heat loss. With this in mind, more research engineers are turning to computer modelling software enabling different process to be assessed at an early stage and speeding implementation of new technology. The main simulation tool used for


computational fl uid dynamics, thermal and structural problems is the fi nite element method (FEM). The main reason for FEM popularity is the diverse number of real-world problems that it can solve, including the ability


www.scientific-computing.com


to handle nonlinear materials and boundary conditions in addition to full transient analysis. The transients may be due to applied sources varying in time or to motional transients. Equally, the method can be applied to electromagnetic problems. As with standard thermal and mechanical


problems the device being simulated has to be divided up into many smaller divisions, referred to as elements, and in three dimensions these are usually brick or tetrahedra elements. The same is true for electromagnetic problems, but with one major difference – not only does the part have to be divided up or discretised, but the exterior around the part has to be discretised as well. This is best illustrated by an example:


suppose we have two simple loops that look like two doughnuts. Into these two doughnuts we impress a current, which will produce a magnetic fi eld. However, not only are we


interested in the magnetic fi eld inside the doughnuts, we are also interested in the magnetic fi eld around them. To do this not only must we divide the doughnuts up into bricks or tetrahedral but, far more problematic, we must divide the air around them into brick or tetrahedra elements as well. These can be simply referred to these divisions as a mesh or fi nite elements mesh. Therefore, unlike the mechanical problem


where we would only have to put a mesh inside the doughnuts, we now have a bigger problem. The air space has to be meshed – a far more diffi cult process then just meshing the doughnuts. To make electromagnetic analysis simpler we would, therefore, like to use a method that avoids having to mesh the media surrounding the device. To circumvent this we need to go back to the basic formulations used to solve electromagnetic problems which requires solving Maxwell’s equations. Maxwell’s equations can be posed in


either integral form or differential form and fi nite element solutions start with Maxwell’s equations in differential form. This requires the entire device as well as the space around it (too some arbitrary distance at least) be meshed. If we start with Maxwell’s equations integral form, however, we can produce a


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