Fracture propagation in porous media during fluid injection

Fluid injection operations [1] are regularly done in several field case scenarios like petroleum production, geothermal installation and underground CO2 storage. Normally fluids with high pressure are injected through the injection wells and sometimes fractures open-up at the well-boundaries. Although fractures are mostly seen as “disturbing elements” for the stability of wells and well-operations, in some cases fractures are “intended” -for example, in hydraulic fracturing scenario people create fractures to increase permeability (flow channels) in the porous rocks. Creation of optimal flow channels is also the main goal for geothermal power projects. However, fractures must be created in a controlled manner so that the well-integrity is not disturbed. Therefore, we need better understanding of physical processes that guide fracture propagation in porous media and we also need to develop tools for monitoring fracture propagation. Our lab experiments [2,3] show the stress-induced fracturing behavior of number of reservoir rocks during fluid injection scenarios. Using the acoustic emission (AE) monitoring system, we could track the major fracture propagation and micro-CT image analysis can show the fracture pattern inside the sample. In addition, we have developed a discrete element model (DEM) simulation code based on invasion percolation and distance dependent stress intensity factor (K) to mimic the stress-induced fracturing of reservoir rocks. Our simulation code can take into account the presence of pre-existing fractures inside the sample. The simulation results agree qualitatively [4] with the experimental observations and such a numerical code can be used to study the entire parameter space with several important inputs like tensile strength distribution, breaking criteria, porosity, sample size, borehole pressure etc. References 1. E. Fjær, R. M. Holt, P. Horsrud, A. M. Raaen and R. Risnes, Petrolum Related Rock Mechanics (Elsevier, 2008). 2. S. Pradhan, A. Stroisz, E. Fjær, J. Stenebråten, H.K. Lund and E. F. Sønstebø, “Stress-induced fracturing of reservoir rocks: Acoustic monitoring and mCT image analysis”, Int. J. of Rock Mechanics and Rock Engineering, DOI 10.1007/s00603-015-0853-4 (2015). 3. S. Pradhan, A. Stroisz, E. Fjær, J. Stenebråten, H.K. Lund, E. F. Sønstebø and S. Roy, “Fracturing tests on reservoir rocks: Analysis of AE events and radial strain evolution”, ARMA (2014). 4. Invited presentation on Fracture propagation during fluid injection: Experiment, modeling and monitoring towards field scale applications at “Fracmeet Conference”, IMSc, Chennai, India in March 2019.