Diagnostic Fracture Injection Tests (DFIT) help to estimate various formation and fracture parameters such as closure stress, reservoir permeability, pore pressure, fracture compliance/stiffness and conductivity of un-propped fractures. All of the above require a precise depiction of the fracture closure process for accurate estimation of the various parameters. The fracture closure process is a strong function of the reservoir parameters such as stress, pressure, and permeability. Heterogeneity of these parameters in the reservoir and the nonlinear behavior of fracture closure with respect to fracture width further complicate the analysis of the observed pressure trends recorded during a DFIT.

In this work, we discuss the application of a 3-D implicitly integrated poroelastic fracture-reservoir-wellbore model to simulate DFITs. The model is validated by simulating a DFIT for a homogeneous formation for which semi-analytical solutions are available. The surface pressure is implicitly calculated by the integrated model during closure of the fracture. The simulated closure pressure response is analyzed, and the results are compared with specified simulation inputs. Various models are used for interpreting the simulated DFIT response to identify the differences between the interpretation methods and validate the numerical simulation.

The numerical model is then used to simulate pressure depletion in a typical unconventional reservoir by a horizontal well with multiple fractures. Our poroelastic model predicts the stress variation in the reservoir induced by depletion. DFIT simulations are then performed in a child well in this asymmetrically depleted environment at various distances from the depleted well. The pressure in the closing fracture is then analyzed to understand the effect of depletion, fracture asymmetry and production duration on the DFIT response.

This work for the first time presents the expected DFIT response in a depleted reservoir (with a non-uniform stress and pore pressure distribution) and the best practices for analyzing such data. Such an analysis cannot be performed by any existing analytical methods and requires poroelastic numerical simulations. The impact of key depletion parameters on DFIT interpretation is explored for the first time. The results from this work can be directly applied to interpret DFIT data acquired in child wells to accurately determine reservoir closure stress, pore pressure, reservoir permeability, fracture compliance and fracture conductivity.