Hydrocarbon production from Shale formations has become an increasingly significant part of the global energy supply since 2010. With the advent of horizontal drilling and multiple-stage hydraulic fracturing, the Utica Shale, which underlies the Marcellus Shale as a natural source rock, is one of the most promising and productive shale plays in the US. However, very few academic papers discuss its geo-stress, pore pressure, permeability, and corresponding DFIT applications, which are essential for the development of the Utica Shale. The objective of this study is to use Diagnostic Fracture Injection Tests (DFITs) data from the field to analyze minimum in-situ stress, closure pressure, reservoir pore pressure, key reservoir properties and fracture geometry in the Utica Shale by different DFIT interpolation methods. The analysis results are compared and discussed in detail to investigate the features of each DFIT interpolation method. In addition, DFIT numerical simulation based on Variable Compliance Model is performed to predict induced fracture geometry and effective formation permeability in the Utica Shale.
DFIT is a commonly applied technique to analyze stress regimes and reservoir properties, while its interpolation can be challenging and difficult for different formations. DFIT interpretation for Shale formations is even more complex. In this study, first overviewing the geology of the Utica Shale and continuing to the summary of DFIT analysis and its governing equations, one can gain a better understanding of the methods and processes used to analyze our DFIT data targeting the Utica Shale. Tangent Line method, Compliance method, and Variable Compliance method are reviewed, and the corresponding assumptions for each method are examined, compared and discussed. Our DFIT data, which is acquired from a horizontal well targeting the Utica Shale, is interpreted by all methods to analyze minimum in-situ stress, closure pressure, initial reservoir pore pressure, key reservoir properties and fracture geometry. The DFIT results are then discussed and compared in detail to investigate the features of each method with its diagnostic signatures. Following that, the induced fracture geometry and the effective formation permeability are predicted by numerical simulation and sensitivity analysis, which also evaluate the impacts of wellbore storage, formation properties and fluid properties on simulated pressure and pressure derivative profiles.
The results from DFIT analysis are very encouraging. The Tangent Line method oversimplified leak off dependence and fracture stiffness, while the obtained minimum in-situ stress, closure pressure, pore pressure, fracture geometry and effective permeability are consistent with the diagnostic plots and our petrophysics studies. The Compliance method is able to identify mechanical closure, but it overestimates the minimum principal stress. The Variable Compliance method can capture the variance in fracture stiffness and pressure dependent leak off during progressive fracture closure, and its estimated closure pressure is an average of the results from the Tangent Line and the Compliance methods. The formation permeability of the Utica Shale is estimated by performing a history match of the pressure and pressure derivative profiles. The physics behind the DFIT simulation and sensitivity analysis is analyzed and discussed in detail. Our study can significantly improve the understanding of pressure/stress regimes, fracture geometry, and reservoir properties in the Utica Shale, as well as features of different DFIT interpolation methods. The knowledge and results demonstrated in this article will indefinitely assist operators in their optimization of multistage fracturing and horizontal drilling design in order to develop the Utica Shale more cost-effectively.
