Geomechanical Well Testing: A New Methodology for Interpretation ofPressure Transient Testing Data for Geomechanical Applications

摘要

Rock mechanics triaxial tests and well logs are the main source for determination of mechanical propertiesof reservoir.These methods obtain values for mechanical properties corresponding to parts of the formationclose to the well area.The experimental approach is much more limited as the coring operation is costlyand is performed in a handful of appraisal/exploratory wells.Here,a novel methodology,geomechanicalwell testing,is presented to estimate the elastic and plastic mechanical properties using pressure transienttesting.In the first part of the paper,the theory of poroelasticity was utilized to develop a geomechanicalwell testing technique,which attains estimation of reservoir's poroelastic properties.The technique is onthe basis of developing a diffusivity equation incorporating mechanical deformation into the fluid transportin porous media and via applying different mechanical boundary conditions,one can obtain several closed-form solutions for storage coefficient.The developed storage coefficients,however,include Poisson's ratio(PR)as the target variable to estimate from conventional well testing.As a verification,a case study wasconducted using the pressure transient data from a sandstone aquifer.Adopting the conventional well testingprinciples,three different values for PR were obtained.The first impression to this point was to decide whichvalue is the most representing value for the aquifer under investigation.We envisioned two methods forthis critical step: 1)comparison of obtained PR values from the geomechanical well testing technique withthe one estimated via another reliable source such as well log/seismic and/or 2)comparison of pressure-time measurements with available numerical simulations.We took this finding for granted and devise a wayto obtain an estimation of dominant boundary conditions of a reservoir.Once the dominant deformationalbehavior was assessed,the technique may be re-implemented along with future well testing measuementsto monitor the evolutions of elastic properties during the life of reservoir.The second part of the paperdeals with another geomechanical well testing technique,which provides a tool for estimation of strengthproperies through developing a generalized diffusivity equation using poroplasticity theory with a plasticpotential function based on Mohr-Coulomb yield/failure criterion.An analytical solution was obtained underuniaxial strain assumption,which can be used to estimate internal friction angle or dilation angle.