Wireline dual-packer mini-fracture testing jobs are used to determine the critical formation breakdown parameters needed for field-scale hydraulic fracture design, water and gas injection management, wellbore stability and sand production. A wireline dual-packer mini-fracture test consists of injection a small volume of fluids at constant flow rate into an open borehole to pressurize the formation and induce fracturing.
The performance of a wireline mini-fracture test and formation failure depends on far-field stress conditions, rock properties (geomechanical properties: elastic properties, strength; microstructural properties: porosity/permeability, pore pressure) as well as operational properties (borehole fluid pressures, flow rates, viscosity). Thus far, wireline mini-fracture tests experienced mixed successes pointing to a need to better predict the expected failure conditions of the formations before application of the wireline dual-packer mini-fracture jobs.
A novel simulator was developed that combines all main parameters (stress conditions, geomechanical & rock properties and operational parameters) controlling the performance of a mini-fracture job and the conditions at which tensile failure should occur near the wellbore. Sensitivity analyses with the simulator showed that rock permeability has the largest influence on the flow rates and fluid-pressure build-up over time. Geomechanical properties as the Young Modulus and Poisson's ratio have a large effect on the fluid pressures needed for tensile failure. Tool specifications determine the maximum fluid pressures that can be reached. The combination of these parameters determines ultimately the possible success or failure of the mini-fracture testing job. The developed simulator can be used to predict the conditions at which tensile failure is expected and can then guide and be compared with actual field tests.