Gas breakthrough experiments on fine‐grained sedimentary rocks

Abstract

The capillary sealing efficiency of fine‐grained sedimentary rocks has been investigated by gas breakthrough experiments on fully water saturated claystones and siltstones (Boom Clay from Belgium, Opalinus Clay from Switzerland and Tertiary mudstone from offshore Norway) of different lithological compositions. Sand contents of the samples were consistently below 12%, major clay minerals were illite and smectite. Porosities determined by mercury injection lay between 10 and 30% while specific surface areas determined by nitrogen adsorption (BET method) ranged from 20 to 48 m2 g − 1. Total organic carbon contents were below 2%. Prior to the gas breakthrough experiments the absolute (single phase) permeability (kabs) of the samples was determined by steady state flow tests with water or NaCl brine. The kabs values ranged between 3 and 550 nDarcy (3 × 10−21 and 5.5 × 10−19 m2). The maximum effective permeability to the gas‐phase (keff) measured after gas breakthrough on initially water‐saturated samples extended from 0.01 nDarcy (1 × 10−23 m2) up to 1100 nDarcy (1.1 × 10−18 m2). The residual differential pressures after re‐imbibition of the water phase, referred to as the ‘minimum capillary displacement pressures’ (Pd), ranged from 0.06 to 6.7 MPa. During the re‐imbibition process the effective permeability to the gas phase decreases with decreasing differential pressure. The recorded permeability/pressure data were used to derive the pore size distribution (mostly between 8 and 60 nm) and the transport porosity of the conducting pore system (10‐5–10‐2%). Correlations could be established between (i) absolute permeability coefficients and the maximum effective permeability coefficients and (ii) effective or absolute permeability coefficients and capillary sealing efficiency. No correlation was found between the capillary displacement pressures determined from gas breakthrough experiments and those derived theoretically by mercury injection.

What’s Conventional and What’s Special in a Reservoir Study for Underground Gas Storage

“…A two-phase fluid flow drainage process is induced through the rock sample in a triaxial cell, which reproduces the in situ confining pressure and stress conditions acting on the rock [10]. The test can be performed and interpreted according to different experimental procedures and approaches [11][12][13]; generally, mercury-air or nitrogen-water systems are utilized in lab experiments and the results are then corrected according to the real gas-water characteristics.…”

Research project on CO2 geological storage and groundwaterresources: Large-scale hydrological evaluation and modeling of impact ongroundwater systems

“…As discussed in Section 3.2.2.3, seal permeability may vary in a wide range from approximately 10 -16 to 10 -23 m 2 (Neuzil, 1994;Hildenbrand et al, 2002Hildenbrand et al, , 2003Hart et al, 2006). Capillarity also plays an important role in trapping CO 2 under a caprock unit because CO 2 , as a non-wetting phase in a saline aquifer, can migrate into the seals only when the pressure buildup in the storage formation is higher than the capillary entry pressure in a CO 2 -brine system.…”

“…The capillary-barrier role of the confining units depends on the contrast of the pressure buildup in the storage formation and the entry pressure of the seals. Confining layers may have a wide range of entry pressures, as measured through laboratory CO 2 -breakthrough experiments (Hildenbrand et al, 2002(Hildenbrand et al, , 2003Li et al, 2005). For example, Hildenbrand et al (2002Hildenbrand et al ( , 2003 reported capillary displacement pressure for CO 2 -brine systems varying from 1 bar to 49 bar.…”

“…Confining layers may have a wide range of entry pressures, as measured through laboratory CO 2 -breakthrough experiments (Hildenbrand et al, 2002(Hildenbrand et al, , 2003Li et al, 2005). For example, Hildenbrand et al (2002Hildenbrand et al ( , 2003 reported capillary displacement pressure for CO 2 -brine systems varying from 1 bar to 49 bar. A value of 210 bar was observed for Mississippian-age Midale Evaporite in the Weyburn Field in southeastern Saskatchewan, Canada (Li et al, 2005).…”

Laboratory Method to Measure Sealing Capacity of Caprocks / Metodyka Wykonywania Pomiarów Laboratoryjnych do Określania Własności Uszczelniających Skał Nadległych

“…Sealing capacity features essentially two parameters: displacement pressure, which begins infiltration of the gas phase into the initially water (brine) saturated pore system of the sealing rock, and the relative permeability to gas phase after the gas breakthrough (Hildenbrand et al, 2002). Relative permeability is a function of the gas/water saturation of the pore system, which is not easy to determine if fine-grained rocks.…”