K.U. Weyer Ph.D., P.Geol., P.HG.
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada

© 2012 K. U. Weyer


Abstract

The poster compares the hydraulic methods of velocity potentials (Muskat, 1937), presently applied in Weyburn investigations of CO₂ sequestration, with the application of hydrodynamic methods of force potentials (Hubbert, 1940) and its consequences on a local and regional scale.

Based on hydrochemical data, Khan and Rostron (2004) adopted the concept that the Weyburn site is under flown within the Mississippian layers by groundwater recharged in outcrop areas of these layers more than 600 km away in Yellowstone National Park and the Big Horn Mountains in Wyoming (Downey et al., 1987; Hannon, 1987; Bachu and Hitchon, 1996). This concept is rejected due to thermodynamic reasons. In the Weyburn field the aquitard (caprock) Watrous layer is permeable to aqueous fluids.

During the exploration phase of the Weyburn field the geologists of Socony-Mobil determined a SW tilted oil/water contact indicating a SW directed groundwater flow in the Midale layer, a part of the Mississippian formation; the oil had been accumulated within an hydrodynamic trap (Hubbert, 1967). Presently, however, a SW to NE directed flow direction has been assumed for the purpose of risk assessment in the ongoing CO₂ sequestration investigation. Based on this concept re-emergence times of 400,000 to 600,000 years have been calculated (Khan and Rostron, 2004).

Within the Mississippian formation of the Weyburn field, Socony-Mobil’s geologists also determined a north to south pointing flow direction (Hubbert, 1967). The logical way to explain the opposite flow directions (presumably at different locations) in the Mississippian within the framework of groundwater flow systems is to assume that the recharge areas for these opposing groundwater flow directions underneath the Watrous caprock (aquitard) are the Moose Mountains towards the NE and the Missouri Coteau and the Wood Mountain to the SW respectively. Accordingly, after penetrating the Watrous aquitard downward in the recharge areas the discharge of these groundwater flow systems would again penetrate the Watrous aquitard on their way upwards into the Souris River and Roughbark Creek.

In fact, east of the Weyburn field, Khan and Rostron (2004) noticed that the vertical pressure distribution could reflect an upward discharge of groundwater through the Watrous aquitard but dismissed this explanation as unlikely, considering a hydraulic discontinuity as "the more likely interpretation of the break". This interpretation has now lost some credibility due to the exploration data reported by Hubbert (1967); these have so far not been considered within the context of the Weyburn CO₂ sequestration.

We expect the groundwater migration times from the Midale to the surface to be in the thousands of years which should be determined by additional hydraulic investigations using the physics of force potentials.

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