Combined rock mechanical and flow tests were conducted on a preserved, partly calcite-cemented natural fracture of a fractured chalk reservoir at in-situ stress and pressure conditions. Stress and pressure changes expected during reservoir production were simulated. A special extensometer setup was applied for improved data quality. Fracture normal stiffness values of 200 MPa/mm were measured at initial in-situ conditions and its stress-dependency can be described with a hyperbolical model. Changes in stress and pore pressure had an equal effect on fracture normal displacement.

Fracture permeability is 6 orders of magnitude larger than the chalk matrix. It is weakly stress-dependent for pore pressure changes present during hydrocarbon extraction following a linear trend. The fracture underwent damage when effective stresses were increased to levels beyond the expected conditions during field production. The nonlinear hydraulic conductivity reduction follows a power-law relationship.

The ratio between hydraulic and mechanical aperture change was constant at 0.2 for stress changes experienced during depletion. It increased to about 0.5 after applying high effective normal stresses that altered the fracture surface. Those findings are qualitatively in line with observations reported from other naturally or artificially fractured rocks.


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