A new microseismic-electromagnetic (EM) acquisition system for reservoir monitoring includes surface and borehole hardware, processing software and interpretation methodology. For heavy oil reservoirs it allows mapping of steam/water flood fronts and surveillance of cap-rock integrity. The new array acquisition architecture combines novel technologies which reduces operational cost, due to unlimited channels capability: EM and microseismic acquisition is in the same receiver node to optimize the synergy between the methods.
While microseismic channels address seal integrity information, EM data are used to track fluids, due to their high sensitivity to the fluid resistivity. The fluid resistivity drops strongly with mobility increase and pore size variation. Dense data further reduce the cost per receiver in a surface location. EM channels provide three-component (3C) electric and 3C magnetic data acquired on the surface and in shallow vertical boreholes. For later versions and deeper reservoirs deep wireline receiver with through casing measurement capabilities are planned. We include in the system an independent physics verification measurement using a differential approach to the surface data called focused source EM (FSEM) with practically little cost.
Carrying out feasibility for each reservoir is key to control risk and cost. The feasibility includes 3D EM modeling, which allows integrating typically complex nature of the reservoir, and on-site EM noise test to tie 3D modeling to actual measured voltages.
3D modeling feasibility for a heavy oil reservoir proves the methodology to monitor the boundaries of the steam flood with accuracy and with high fidelity. Above the edges of the flooded (higher-temperature – lower-resistivity) area the results predict time-lapse EM anomaly exceeding 500%.
The entire system is coupled with processing and 3D modeling/inversion software, significantly streamlining the workflow for the different methods.
The system is capable of measuring and integrating the 3C of the electric field and 3C of the magnetic field in order to map the steam front and at the same time measuring microseismic occurrences in order to monitor seal stability. Channels capability of the system is practically unlimited allowing a denser coverage of the area in order to increase resolution and improve inversion.