Petrophysical Properties of Tight Gas Reservoir Sandstones from the Southern North Sea

Abstract

The Southern North Sea contains several “tight gas” reservoirs, mainly found in the Rotliegend and Triassic Main Buntsandstein. To investigate two-phase (gas/water) fluid transport processes in low-permeable sandstone reservoirs a sample set consisting of fine- to medium- grained sandstones was selected from several wells. The investigations comprise the determination of basic petrophysical properties, the conduction of single- and two-phase fluid flow measurement and characterization of the pore system by helium pycnometry, mercury porosimetry and nitrogen adsorption. The fluid transport experiments are conducted in two different types of cells, an isostatic flow cell (DIN 18 130), working at room temperature and low confining pressures (0.25 MPa) and a triaxial flow cell with confining pressures up to 50 MPa, 100 kN axial load and temperatures up to 100°C, comparing steady state and unsteady state methods. First results yielded water permeability coefficients in the microdarcy (µD) to millidarcy (mD) range. Klinkenberg corrected gas permeability tests with argon (Ar) yielded permeability coefficients in the µD range. Gas breakthrough experiments are conducted with a double-walled burette system for simultaneous measurement of water and gas flow. Capillary entry pressures were less than 0.17 MPa and effective gas permeabilities after gas breakthrough in the µD range.