In oil and gas production environments, controlled-source electromagnetics can be used to aid brownfield exploration, development, and reservoir monitoring efforts. However, such environments typically have many highly conductive steel-cased wells in the area of interest. In this paper, we present a modeling algorithm using a method of moments approach to calculate the electromagnetic response of multiple 3D steel-cased wells of arbitrary geometry in a layered earth conductivity model. First, we divide each casing into a collection of segments, each carrying a uniform current density. Next we create a matrix that describes how the casing segments interact with each other electromagnetically. Then we solve a linear system for the current within each casing segment, given a transmitter of arbitrary frequency and location. From these currents we are able to solve for the secondary electromagnetic fields produced solely by the casings at any point in our layered model, and add these to the primary fields produced by the transmitter. To validate the algorithm, we compare results with the pseudo-analytic method of moments algorithm for a single vertical casing in a halfspace. We also compare results with a finite-element solution using COMSOL for both a single vertical and single tilted well buried in a layered earth. Results show a good match between these different approaches, which improves with increasing subsurface resistivity. Finally, we apply our algorithm to a realistic synthetic model with three casings (one vertical and two deviated) extending into a layered earth model containing the classic thin resistive layer. This example illustrates how the algorithm can be used to compute the electromagnetic response of multiple steel-casings. The example also illustrates how the electromagnetic field changes due to the presence of the casings and how signal is able to be injected at depth by utilizing the casing.
|Commitee:||Ganesh, Mahadevan, Li, Yaoguo, Sava, Paul|
|School:||Colorado School of Mines|
|School Location:||United States -- Colorado|
|Source:||MAI 56/03M(E), Masters Abstracts International|
|Subjects:||Geophysics, Geophysical, Electromagnetics|
|Keywords:||Controlled-source electromagnetics, Finite-element method, Method of moments, Steel-cased wells|
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