Improving reservoir characterisation and simulation using near-wellbore upscaling
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In this thesis, novel workflows involving high resolution near-wellbore modelling (NWM) are illustrated, which allow integration of multi-scale geological and petrophysical data from highly heterogeneous reservoirs in field-scale reservoir simulations. When applied to a clastic reservoir with high variance at small scale, NWM significantly improved reservoir characterisation and calibration of reservoir model with well test data. Results show that using NWM tools for reservoir modelling yields more precise flow calculations and improves our fundamental understanding of the interactions between the reservoir and the wellbore. Furthermore, this thesis employs an integrated NWM workflow to identify and evaluate the geological heterogeneities that enhanced reservoir permeability in a giant carbonate reservoir with a long production history. Key among these heterogeneities are mechanically weak zones of solution-enhanced porosity, leached stylolites and associated tension gashes, which were developed during late stage diagenetic corrosion. The results of this investigation confirmed the critical role of diagenetic corrosion in enhancing the permeability of the reservoir. One of the key aims of this thesis is to develop a novel near-wellbore upscaling (NWU) workflow that addresses the challenges associated with conventional carbonate modelling workflows. The NWU workflow developed in this thesis provides a systematic geostatistical approach to obtain more realistic representation of the above multi-scale geological-petrophysical heterogeneities in the reservoir simulation model of the carbonate field. The NWU results were used to generate global porosity-permeability and vertical-horizontal permeability relationships for reservoir simulation. Instead of applying artificial permeability multipliers that do not necessarily capture the impacts of geological heterogeneities, the NWU workflow incorporates representations of fine-scale heterogeneities in the reservoir simulation model. Another aim of this thesis is to develop a new near-wellbore rock-typing and upscaling approach to improve the integration of reservoir rock-typing and simulation in carbonate reservoirs. The rock-typing and upscaling methodology described in this work involves the geological-petrophysical classification of the reservoir heterogeneities through systematic evaluation of the key diagenetic events, including the key associations between the depositional and diagenetic features, and their impact on reservoir flow properties. The near-wellbore rock-typing and upscaling workflow yielded consistent initialisation of the reservoir simulation model and therefore improved the calculation of volumes of fluids-in-place. Subsequently, the cumulative production curves computed by the reservoir simulation model agreed well with the historic production data. The revised simulation model is now much better constrained to the reservoir geology and provides an improved geological-prior for history matching. This thesis therefore provides valuable insights to the means by which a geologically consistent field-level history match can be achieved for complex carbonate reservoirs.