Pore Pressure Prediction, Hydraulic Fracture Propagation and Huff-and-Puff Gas Injection in Naturally Fractured Shale and Tight Petroleum Reservoirs
Date
2021-09
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Abstract
This dissertation explores links between the pore pressure prediction, hydraulic fracture modelling and improved oil recovery in unconventional reservoirs by examining the geomechanical implications of the Biot coefficient on hydraulic-fracturing-induced fault slip, and the effect of hydraulic fracture geometry on the performance of cyclic gas injection. To do so, this thesis develops the following original contributions: • A new pore pressure prediction model for shales and organic-rich rocks that accounts for the effect of active hydrocarbon generation. The key aspect is the determination of the in-situ Biot coefficient using well logs and formation pressure tests. The majority of the available pore pressure estimation models rely on empirical parameters extracted from statistical analysis and best-fit exercises. While these models have proven useful, the empirical parameters they use are case-dependent and difficult to determine in areas with little or no regional experience. The new pore pressure estimation workflow, on the other hand, follows a physics-based approach and does not rely on the use of fitting parameters. • The formulation of a hydraulic fracture model that features a rock mechanics solution that is exact, based upon the concept of Airy stress functions, which are functions of complex variable for solving stress problems in elastic media. The rock mechanics solution is able to track accurately both the fracture height and width in multilayered reservoirs and compares well with the finite element and the displacement discontinuity methods. • A new, semi-analytical material balance equation (MBE) for production forecasting of unconventional oil reservoirs performing under cyclic gas injection. The main advantage of the new MBE relies on its capability to provide quick yet accurate estimates of oil recoveries and rates as a function of time. It is concluded that overpressure caused by hydrocarbon generation in shales and organic-rich rocks can lead to Biot coefficients larger than unity. The Biot coefficient has important geomechanical implications in the context of hydraulic-fracturing-induced fault slip. Increasing values of the Biot coefficient reduce the effective normal stress on faults, and some of these faults may become critically stressed regardless of their orientation. Furthermore, hydraulic fracture geometry significantly affects the performance of cyclic gas injection.
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Keywords
Pore Pressure, Hydraulic Fracturing, Huff-and-Puff Gas Injection, Unconventional Reservoirs
Citation
Orozco Ibarra, D. R. (2021). Pore pressure prediction, hydraulic fracture propagation and huff-and-puff gas injection in naturally fractured shale and tight petroleum reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.