UC Riverside

Diagnostic Fracture Injection Tests (DFIT) are techniques that have been widely used in hydraulic fracturing to estimate reservoir properties and parameters. A fully coupled poroelastic model is developed to simulate hydraulic fracture initiation, propagation, and closure using the finite element method. The pressure decline data after shut-in is analyzed to estimate the leak-off coefficient, in-situ stress, permeability, and pore pressure. Results are compared to previous DFIT techniques developed based on linear elastic fracture mechanics and Carter’s leak-off model. During the before-closure analysis, the pressure decline data is analyzed to estimate the leak-off coefficient and in-situ stress through a special dimensionless time function called G-function. With poroelastic effects taken into account, the leak-off coefficient can be twice as large as the one obtained from previous DFIT techniques. Also, higher in-situ stress estimates are obtained in the fully coupled model. The after-closure analysis involves the identification of linear flow and radial flow regimes. The linear flow analysis can significantly overestimate reservoir permeability, while the radial flow analysis can obtain a reliable permeability estimate. Both the linear and radial flow analyses can provide accurate estimates of pore pressure. This study demonstrates that poroelastic effects cannot be ignored in some cases. The previous DFIT techniques developed based on linear elastic fracture mechanics and Carter’s leak-off model may result in inaccurate estimation of properties such as leak-off coefficient and permeability, further affecting the optimization of hydraulic fracturing treatment design.