Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements

• Published in: International journal of rock mechanics and mining sciences (Oxford, England : 1997) England : 1997), 2004-12, Vol.42 (2005)
• Main Authors: Cappa, Frédéric, Guglielmi, Yves, Fénart, Pascal, Merrien-Soukatchoff, Véronique, Thoraval, Alain
• Format: Article
• Language: English
• Subjects: Earth Sciences; Engineering Sciences; Hydrology; Mechanics; Sciences of the Universe; Solid mechanics
• ISSN: 1365-1609; 1873-4545

Hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses. The experiments consist of hydraulic loading/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes. Hydromechanical response of the reservoir was measured using six pressure–normal displacement sensors located on discontinuities and two surface tiltmeters. A dual hydraulic behavior was characterized for low-permeability bedding planes well connected to highpermeability faults. Displacement responses show high-variability, nonlinear changes, sometimes with high-frequency oscillations, and a large scattering of magnitudes. Initial normal stiffnesses and effective normal stresses along fault planes were estimated in the field by interpreting pressure–normal displacement relations with a nonlinear function between effective normal stress and normal displacement. Two-dimensional discontinuum modeling with transient fluid flow was performed to fit measurements during hydraulic loading tests. Results show that the hydromechanical behavior of the reservoir is restored if a high stiffness contrast is allocated between low- and high-permeability discontinuities. Thus, a dual-permeability network of discontinuities will likely also be a contrasting stiffness network, in which the deformation of major flow-conducting discontinuities is significantly influenced by the stiffness of the surrounding less-permeable discontinuities.