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45250-AC9
Magnetic Resonance Imaging of Oil/Water Flow through Fractures

Matthew Becker, State University of New York at Buffalo

The relative permeability of oil/water flow through rock fractures is a function of rock characteristics and fluid properties. Observations in glass and plastic rock models have shown that multiphase fluid flow through fractures is channelized and highly dynamic. The non-wetting phase forms ganglia that exhibit short-term breakthrough and snap-off behavior, and water exhibits intermittent bypassing. Although studies have measured relative permeability of multiple phases in rock cores, these have not been tied to imaging. Consequently, relative permeability in fractures is not well understood from a phenomenological stand point.

In this project we measure head drop across a rock core during infusion of wetting and non wetting phases (water/oil) to determine relative permeability, while at the same time imaging fluid movement using magnetic resonance imaging. The pressure drop across the water/oil interface is a function of the radius of curvature in the front (contact angle), which in turn is a function of contact angle (surface wettability), geometry (fracture aperture), and elevation (sample orientation). We can independently measure all three variables using the MR experimental procedure.

In Year 1 we have focused on the bench-top experimental set up in preparation for the MR imagery. MR imaging time is expensive so it is important that pressures can be carefully measured before imaging begins. We are investigating two methods of measuring pressure loss across the fracture. The first is a simple differential pressure transducer that has an accuracy of approximately 22 Pa or 2.2 mm of water. The second approach is to use a displacement meter with a manometer which has a potential accuracy of 0.003 mm of water or less. The accuracy of the differential pressure transducer is marginal with respect to expected pressure differential in the experiments. On the other hand, manometers can be logistically difficult because of fluid reactivity and inertial effects of the fluid column. We are currently evaluating these alternatives using glass and rock models of varying capillary diameter.

We collected multiple samples of naturally fractured Potsdam sandstone cores from the Altona Flat Rock site near Plattsburgh, New York. Using our handheld corer, however, proved difficult and we were able to collect cores of only 10 cm in length. We would like 25 cm cores. A sliding carriage was constructed by our machine shop consequently, and we will return to the field site this fall to collect larger specimens with the new setup.

During Year 1 it was not possible to assign a full time student to the project. The start date of the grant was past our usual recruitment period. Consequently, a graduate student fully dedicated to the project began September 1, 2007. The previous student supported on this project was able to dedicate only one semester for which he was supported as a Research Assistant. The PI has been trying to make up for lack of student support with additional time in the laboratory.

Expected Milestones:

• December, 2007 Benchtop experiments complete and start in the MR lab

• January 2008 Begin MR imaging

• May 2008 Imaging complete

• August 2008 Interpretation complete and draft publication sent to J. Geophysical Research.

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