Upscaling of Geomechanics in Heterogeneous Compacting Reservoirs

Abstract

Upscaling of properties for reservoir simulation has reached a stage of maturity and uses sophisticated techniques. In contrast, little work has been done on upscaling of mechanical properties for coupled modeling, and the geomechanical model is usually assumed to be representative (upscaled) without actually being subjected to the same rigor of process or scrutiny. Compacting reservoirs often contain fine sand-shale sequences on sub-grid scale (compared to flow modeling grid) and are typically represented in simulators by the net-to-gross (NTG) concept, while being ignored in geomechanical modeling.In this work, we present a method to upscale shales in the geomechanical component of a coupled simulation by computing dynamically changing equivalent moduli. The method is based on estimating the depletion of interbedded shales, coupled with analytical solutions for equivalent moduli under the assumption of uniaxial deformation. The technique has been verified by sub-grid scale simulations and requires geometric characterization of the shales but is relatively simple and can be easily implemented in coupled simulators. The analysis shows that the inclusion of the shales generally reduces computed compaction, with the controlling variables being NTG, dimensionless pressure depletion of the shales (which in turn depends on their flow properties) and mechanical properties of the shales.The approach developed was incorporated in the subsidence and compaction analysis over a complex offshore oil reservoir. The reservoir zone consisted of a number of intervals that included relatively undeformed as well as highly deformed layers, and on reservoir model scale had significant NTG ratios. A comprehensive study (based on coupled flow and geomechanics simulation) was conducted to evaluate well integrity, fault slip (reactivation) and compaction drive. A large full field model was built using data from a multitude of sources and production data was modeled and history matched, allowing us to estimate the magnitude of reservoir subsidence and the contribution of the NTG effect on predictions. The study presented here showed that in the absence of any consideration of the NTG effect, predictions (for compaction and subsidence) could be significantly overestimated. In addition, the method can be used to study the phenomena of "time-lag" of subsidence which has been observed in some reservoirs.

Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

“…While large-scale karst and fault structures can be spatially interpreted from geophysical data (seismic surveys, downhole logging), small-scale heterogeneities are almost unresolvable (Egert et al 2018). However, by defining common parameter ranges for different rock and facies types of the Malm carbonates by laboratory tests, as done in this study and in the studies of Bohnsack et al (2020) and Potten (2020), heterogeneity can be controlled even in a coarser modeling grid of numerical simulations (e.g., THM models) by up-scaling these value ranges for different lithologies (Settari et al 2013). The acquisition of various rock parameters at laboratory scale can, therefore, help to predict the thermal-hydraulic-mechanical behavior of the reservoir and reduce the exploratory and economic risk of new geothermal projects in the Bavarian Molasse Basin by closing the gap between rock core data and reservoir scale.…”

Triaxial testing and hydraulic–mechanical modeling of sandstone reservoir rock in the Upper Rhine Graben

“…z-direction as a function of time in agreement with the triaxial experiments, while the stress acting on the lateral surface is kept constant. Since the focus is on the deformation processes and their coupled effects on sample and reservoir scale, the experimental results are averaged and used as constant input parameters for the numerical evaluation (Khajeh 2013;Settari et al 2013).…”

“…The recent progress in hardware and software development allows calculating the complex coupling of physical processes in a natural and perturbed geoscientific environment at efficient computation times (Kohl and Hopkirk 1995;O'Sullivan et al 2001;Watanabe et al 2017). The experimental results of different tests, like triaxial or permeability tests, carried out with a permeameter can also be used as input and calibration parameters to upscale the laboratory to reservoir data (Settari et al 2013).…”