Abstract
The "Shale Engineering" approach and modeling addresses production forecasting in shale and tight formations. This new reservoir simulation methodology relies on modeling the propagation of the stimulated rock volume from the near-well vicinity to deep into the formation. Simulation models are built for individual fracturing stages and validated by matching treatment pressures and rates while conforming to geomechanical and microseismic observations. Stage models are then combined into a larger well model where individual stage contribution and early production performance are matched. This approach was applied on a project that was developed by EQT in an Upper Devonian shale formation in West Virginia. Data available for this project included fit-for-purpose formation evaluation description, production logs and downhole microseismic data with advanced processing and interpretation. The results provided a good match to early well performance, despite the complexity of having to match a combination of shales and partially depleted tight sandstones that had been stimulated by foam fracturing with proppant. This approach can be used not only to predict production, but also as a practical platform for field development design and optimization. Furthermore, the matched results validated the shear stimulation model developed by the authors for this type of application. The approach makes it possible to exploit microseismic observations in a more realistic way in order to describe the stimulated rock volume (SRV), and it explains early-life production logs that indicate uneven fracturing stage contribution. The model also can relate stimulation effectiveness to pre-existing formation rock and fluid properties, and thus can be used as a guide to identify optimal formation targets. The "Shale Engineering" approach hinges on the premise that when unconventional "tight rocks" containing hydrocarbons are modified by hydraulic fracture stimulation, the process converts them into "reservoir rocks". In addition, interpretation of the newly created "artificial reservoirs" is accomplished through multi-displinary expertise that is focused on providing a rate performance and predictive model to aid in reservoir development. Because unconventional resource/reservoir formations are unique and subject to a wide range of conditions, they require a production predictive method more suitable for this task than the commonly used "Type Curves". The advantage of the "Shale Engineering" approach is that it allows validation with parameters that can be available at an early stage of the well life, which in turn are useful to constrain model solutions. It also offers the means to include geomechanics in a practical workflow that allows systematic workflow allows for step-by-step validation of the model. The suggested simulation process uses commerical software and it can be applied to either simple or complex cases.
