UBC Theses and Dissertations

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UBC Theses and Dissertations

Detecting and imaging time-lapse conductivity changes using electromagnetic methods Devriese, Sarah G. R.


Steam-assisted gravity drainage (SAGD) is an in situ recovery process used to extract bitumen from the Athabasca oil sands in Northern Alberta, Canada. The steam heats the oil, allowing it to be pumped to the surface. The success of this technique depends on being able to propagate steam throughout the reservoir but irregular growth may occur due to the heterogeneity of the reservoir. This affects the amount of oil that is produced and illustrates the need to monitor steam chamber growth. The steam affects the electrical conductivity of the reservoir, thus creating a physical property contrast. This thesis investigates how electromagnetic methods can be used to monitor the time-lapse conductivity changes due to SAGD processes. A simple but illustrative survey design procedure was developed to examine a variety of field surveys that include surface and borehole transmitters operating in the frequency or time domain. Compared to standard DC resistivity surveys, the ability to resolve the steam chamber is significantly enhanced using EM. Notably, the feasibility study showed that the steam can be recovered using a low-cost large-loop surface transmitter and borehole measurements, despite the shielding effects of the overlying conductive cap rock. When applied to an example based on a field site, this survey recovered the synthetic steam chambers and discerned an area of limited growth that resulted from a blockage in the reservoir. At a different field site, the reservoir is too deep to use surface methods but steam growth was monitored using crosswell DC resistivity. The sensitivity matrix shows that these electric crosswell surveys do not contain enough information to image the entire reservoir between the wells. By extending to multi-frequency electromagnetic methods using the same survey design, the sensitivity to the reservoir increased and allowed for recovery of the steam chambers. Electromagnetic methods also provide valuable information about the background conductivity of the layers above the reservoir, including structures such as paleo-channels and the conductive cap rock. By using airborne, surface-based, and downhole surveys, I show that the Athabasca oil sands can be explored and monitored using electromagnetic methods.

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