Gas breakthrough experiments on pelitic rocks: comparative study with N₂, CO₂ and CH₄

Abstract

The capillary-sealing ef®ciency of intermediate-to low-permeable sedimentary rocks has been investigated by N 2 , CO 2 and CH 4 breakthrough experiments on initially fully water-saturated rocks of different lithological compositions. Differential gas pressures up to 20 MPa were imposed across samples of 10±20 mm thickness, and the decline of the differential pressures was monitored over time. Absolute (single-phase) permeability coef®cients (k abs ), determined by steady-state¯uid¯ow tests, ranged between 10 À22 and 10 À15 m 2 . Maximum effective permeabilities to the gas phase k eff (max), measured after gas breakthrough at maximum gas saturation, extended from 10 À26 to 10 À18 m 2 . Because of re-imbibition of water into the interconnected gas-conducting pore system, the effective permeability to the gas phase decreases with decreasing differential (capillary) pressure. At the end of the breakthrough experiments, a residual pressure difference persists, indicating the shut-off of the gas-conducting pore system. These pressures, referred to as the`minimum capillary displacement pressures' (P d ), ranged from 0.1 up to 6.7 MPa. Correlations were established between (i) absolute and effective permeability coef®cients and (ii) effective or absolute permeability and capillary displacement pressure. Results indicate systematic differences in gas breakthrough behaviour of N 2 , CO 2 and CH 4 , re¯ecting differences in wettability and interfacial tension. Additionally, a simple dynamic model for gas leakage through a capillary seal is presented, taking into account the variation of effective permeability as a function of buoyancy pressure exerted by a gas column underneath the seal.

Geogas transport in fractured hard rock – Correlations with mining seismicity at 3.54km depth, TauTona gold mine, South Africa

“…Number "1" indicates the broad CO 2 mid-day peak, "2" the afternoon geogas peaks. For further details, see 4.1.3 Technical improvements regarding gas analysis Figure 8: Strip cartoon of gas breakthrough initially water saturated fractures (a) Initially water saturated fractures are not permeable to advective gas flow, (b) sporadic gas breakthrough is possible as soon as the pressure difference ∆P between the borehole and the tunnel exceeds the capillary pressure threshold P c, threshold (c) re-clogging by water due to surface tensions; (Hildenbrand et al, 2004) . Far distant seismic events (leftist "1", ~1 km) do significantly increase the calculated cumulative seismic moment, but have no effect on the borehole gas composition (not shown).…”

Impact of Effective Pressure on Threshold Pressure of Kazusa Group Mudstones for CO₂ Geological Sequestration

“…5,19) Gas breakthrough pressure experiments using CO 2 /water or CO 2 /brine systems have mainly identified the above linear correlation between the permeability and threshold pressure for mudrocks such as clay and silt-rich rocks. 5) Furthermore, systematic experimental studies on gas breakthrough behavior of Hg/Air, N 2 /water, CO 2 /water, and CH 4 /water have been reported by Hildenbrand et al 24) They indicated that data for all the other systems of CO 2 /water also had linear correlations similar to the case of the CO 2 /water system, yet being wide variation in the measured values.…”

High-Resolution 3D FIB-SEM Image Analysis and Validation of Numerical Simulations of Nanometre-Scale Porous Ceramic with Comparisons to Experimental Results

“…Low permeability formations are often of significant interest in petroleum engineering applications as they form the seal, or cap rock, above hydrocarbon reservoirs (Boulin et al 2013;Harrington and Horseman 1999;Hildenbrand et al 2002;Schlomer and Krooss 1997;Thomas et al 1968). They are important to carbon storage operations as a major trapping mechanism, specifically physical trapping (Amann-Hildenbrand et al 2013;Boulin et al 2011;Hildenbrand et al 2004;Li et al 2005;Wollenweber et al 2009Wollenweber et al , 2010. Increasingly, these systems also play a large role in the behaviour of unconventional hydrocarbon recovery processes such as shale gas operations (Javadpour et al 2007;Sakhaee-Pour and Bryant 2012).…”