Network Connectivity in low-permeability Carbonates

Open fracture networks flow paths in low permeability rocks, are highly sensitive to changes in aperture. Even high resolution X-ray tomography-derived aperture distributions and connectivities cannot accurately predict bulk or local     flow characteristics, especially if matrix pore systems contribute.

Here XRT reconstructions of experimentally-fractured low-permeability laminites are accompanied by neutron beam radiography and tomography, where first dense then normal water are injected into the sample base.

To our knowledge this is the first identification of fluid front movement through fracture arrays using neutron tomography.

Samples of a very fine-grained laminite, a lacustrine layered carbonate rock “grain size” 5µm, were deformed experimentally to represent 1 to 2 km burial depth, creating a partially interconnected series of shear- and extension-fractures (Fig. 1) that the XRT indicated were partly open under atmospheric conditions.

Continuous radiography and periodic (3D) tomography (Figs 2 & 3) are used to record movement of dense (deuterated) water, injected at the base under pressure control, until this water reaches the sample top. Distilled water is then injected and progression of normal water through the (mostly) deuterated water saturated sample is monitored.