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Migration

Since several years our group is experimentally investigating the transport characteristics of low-permeable sedimentary rocks (down to nDarcy-range). Both, pressure driven flow and molecular diffusion of hydrocarbon and non-hydrocarbon gases through water-saturated rocks are taken into account. The measurements are either conducted under single-phase or two-phase conditions.

All available petrophysical, mineralogical and geochemical parameters are compiled in a mudrock database.

Measurements performed in the lab

Pressure-driven volume flow (Darcy flow:)

• single-phase flow (water, brine): absolute permeability (k_abs)
• two-phase (water, sub- and supercritical CO₂, CH₄, N₂, Ar, He): effective permeability to the gas phase (k_eff)
• capillary sealing efficiency: minimum capillary displacement pressure (P_threshold, or P_breakthrough) or snap-off pressure

Molecular transport (diffusion) of dissolved gas (CO₂) in water-saturated sedimentary rocks

Fluid flow measurements are performed in triaxial flow cells designed for confining pressures up to 50 MPa (500 bar), axial load of up to 100 kN and maximum temperatures up to 350°C.

Figure legend: (A) stainless steel body; (B,C) 1/8" conduits; (D) connector for confining pressure; (E) cylindrical rock sample (28.5 mm diameter); (F) porous stainless steel disks (fluid reservoirs); (G) graphite packing material; (H) stainless steel pistons; (I) confining pressure compartment; (K) double-layered sleeve; (L) axial load.

P_{c, max} = 500 bar
F_axial = 100 kN
T_max = 350 °C

Sample plugs are placed between two porous stainless steel disks and two stainless steel pistons equipped with boreholes for fluid introduction and removal. The outer surface of the sample/piston arrangement is sealed with a double-layered sleeve. The inner sleeve consists of lead (Pb) foil (0.15 mm thickness); for the outer layer either thin-walled copper (Cu) or aluminum (Al) tubes are used.

Application of the confining pressure (D, Figure above) of at least 300 bar ensures a leak-tight seal around the sample plugs. The efficiency of the double-layered sleeve system has been tested extensively in gas diffusion experiments (e.g. Schlömer & Krooss, 1997).

The same sample arrangement is used for

1.  single phase permeability measurements

2.  gas breakthrough experiments

3.  and diffusion experiments

Busch, A., Alles, S., Gensterblum, Y, Prinz, D., Dewhurst, D.N., Raven, M.D., Stanjek, H., Krooss, B.M. (2007): The CO2 storage potential of shales. International Journal of Greenhouse Gas Control, submitted.

Hildenbrand A., Schlömer S., Krooss B. M. (2002). Gas breakthrough experiments on fine-grained sedimentary rocks. Geofluids, 2, 3-23.

Hildenbrand A., Krooss B. M., Schlömer S., Littke R. (2003). Dynamic gas leakage through fine-grained seal lithologies. EAGE Conference 8.-11.September 2003: Fault and Top Seals. What do we know and where do we go?, O-15, 1-10.

Hildenbrand A., Schloemer S., Krooss B., Littke R. (2004). Gas breakthrough experiments on pelitic rocks: comparative study with N2, CO2 and CH4. Geofluids, 4, 61-80.

Krooss, B. M., Leythaeuser, D. (1996). Molecular diffusion of light hydrocarbons in sedimentary rocks and its role in migration and dissipation of natural gas. In: D. Schumacher, M. A. Abrams (eds), Hydrocarbon migration and its near-surface expression, AAPG Hedberg research conference, Vol. 66, pp. 173-183.

Krooss, B. M., Schlömer, S. & Ehrlich, R. (1996). Experimental Studies on the Hydrocarbon Sealing efficiency of Pelitic rocks. In: Fluid Flow Through Faults and Fractures in Argillaceous Formations. - Joint NEA/EC Workshop, Bern, Suisse, June 10-12.

Krooss B. M., Leythaeuser D., Schaefer R. G. (1988). Light hydrocarbon diffusion in a caprock. Chemical Geology. 71, 65-76.

Schloemer S., Krooss B. M. (1997). Experimental characterization of the hydrocarbon sealing efficiency of cap rocks. Marine Petrol.Geol., 14(5), 565-580.

Schloemer S. Krooss B. (2004). Molecular transport of methane, ethane and nitrogen and the influence of diffusion on the chemical and isotopic composition of natural gas accumulations. Geofluids 4(1), 81-108.

Wollenweber, J., Alles, A., Busch, Stanjek, H., Krooß, B.M. (2008). Effects of CO2 on the sealing efficiency of pelitic caprocks. Workshop on Numerical Models for CO2 Storage in Geological Formations in Stuttgart, April 2-4, 2008 (presentation).