Experimental investigation of CO ₂ breakthrough and flow mechanisms in shale

Abstract

Supercritical CO 2 breakthrough and flow mechanisms in shale have been investigated in laboratory experiments using a high pressure flow cell and cylindrical samples of shale from the Draupne formation in the North Sea. The main objective is to study the basic mechanisms involved in the breakthrough process and define the controlling parameters for supercritical CO 2 flow in a low permeable shale.Experimental testing provides new insight into the CO 2 breakthrough process through simultaneous measurements of deformation and ultrasonic velocities in the sample. A marked sample dilation associated with the CO 2 breakthrough is identified accompanied with a pronounced drop in ultrasonic velocities. X-ray images of the sample using a high resolution 3D computer tomography (CT) scanner provide information on macroscopic fracture distribution inside the sample before and after testing.The CO 2 breakthrough pressure for the Draupne material seems to depend on confining pressure and effective pressure rather than pore pressure difference across the sample. After breakthrough the effective CO 2 permeability was found to follow a simple model for permeability in fractured rock. The drop in ultrasonic velocity was associated with mechanical changes and possible micro fracturing inside the sample. Based on our observations we conclude that pressure-induced opening of micro-fractures during the breakthrough process is an important mechanism for flow in addition to capillary displacement. Our findings may have important consequences for later testing and estimation of CO 2 breakthrough pressure and flow in shale.

Sorption and changes in bulk modulus of coal — experimental evidence and governing mechanisms for CBM and ECBM applications

“…8) is of the type commonly observed in uniaxial loaded, fractured rocks (i.e. irreversible, but closely recoverable -David et al, 2012;Jaeger et al, 2007;Walsh, 1965), but also in the case of isostatic loading of anisotropic rocks (see Skurtveit et al, 2012 for a North Sea shale sample exposed to brine). Furthermore, a comparison of the magnitude of apparent bulk moduli obtained here with the bulk moduli obtained through ultrasonic velocity measurements (Morcote et al, 2010;Schuyer et al, 1954) yield relatively low values both in the evacuated and fluid-equilibrated states.…”

Gas Transfer Through Clay Barriers

“…Caprock integrity studies from a number of North Sea hydrocarbon fields (Angeli et al, 2009;Harrington et al, 2009;Skurtveit et al, 2010Skurtveit et al, , 2012 indicate dilatancy may be a common mechanism associated with caprock failure. Laboratory experiments injecting carbon dioxide through samples of Draupne shale show a clear increase in volume during gas flow (Angeli et al, 2009;Skurtveit et al, 2010Skurtveit et al, , 2012. Simultaneous measurements of P and S wave acoustic velocity show a change in behaviour as CO 2 moves through the sample, and is related to mechanical changes in the sample.…”

“…The focus of carbon capture and storage (CCS) studies is on the analysis of the longterm sealing efficiency of lithologies above depleted reservoirs or saline aquifers, typically at larger depths (hundreds to thousands of meters). During the last decade, several studies were published on the sealing integrity of clay-rocks to carbon dioxide (Hildenbrand et al, 2004;Li et al, 2005;Hangx et al, 2009;Harrington et al, 2009;Skurtveit et al, 2012;AmannHildenbrand et al, 2013). In the context of petroleum system analysis, a significant volume of research has been undertaken regarding gas/oil expulsion mechanisms from sources rocks during burial history (Tissot & Pellet, 1971;Appold & Nunn, 2002), secondary migration (Luo et al, 2008) and the capillary sealing capacity of caprocks overlying natural gas accumulations (Berg, 1975;Schowalter, 1979;Krooss, 1992;Schlömer and Kross, 2004;Li et al, 2005;Berne et al, 2010).…”

An Experimental Investigation of Hydraulic Fracturing in Shale Considering Anisotropy and Using Freshwater and Supercritical CO2

“…Chen et al [14] microscopically observed the induced fractures of granite, further confirming that the viscosity of the fracturing fluid affects the fracture propagation, and that the fracture induced by SCO 2 has more branches along the fracture than a fracture produced by freshwater and viscous oil. Skurtveit et al [15] investigated the SCO 2 breakthrough and the flow mechanisms in shale. They discovered that the pressure-induced micro-fractures that occurred during the breakthrough process, in addition to the capillary displacement, are important flow mechanisms.…”