Effect of rock and wettability heterogeneity on the efficiency of WAG flooding in carbonate reservoirs

Mohamed Ahmed Elfeel, Adnan Rashid Saif Al-Dhahli, Zeyun Jiang, Sebastian Geiger, Marinus Izaak Jan Van Dijke

Research output: Chapter in Book/Report/Conference proceedingConference contribution

18 Citations (Scopus)


Carbonate reservoirs contain more than half of the world's remaining petroleum reserves and are increasingly becoming targets for water-alternating-gas (WAG) flooding as secondary or tertiary recovery. Heterogeneity in carbonate reservoirs spans from pore- to reservoir-scale. This is exacerbated by the presence of natural fractures and post-depositional dissolution. Furthermore, carbonate reservoirs tend to have variable wettability that impacts fluid flow which adds to reservoir uncertainty and renders managing WAG floods difficult. In this work, we examine the effect of rock and wettability heterogeneity on recovery profiles in naturally fractured carbonate reservoirs (NFCR). To simulate WAG flooding in NFCR with arbitrary wettability, we use saturation functions derived from a state-of-the-art pore network model to preserve multi-scale heterogeneities at the pore-scale. We study the interplay of capillary, gravity and viscous forces at an intermediate scale, then simulate WAG flooding in the presence of fractures in a heterogeneous carbonate ramp outcrop model. Adding the permeability and wettability heterogeneities impacts ultimate recoveries during water injection cycles by up to 6% and 14% absolute, respectively. Both heterogeneities affect the speed of recovery during gas injection cycles. Depending on its relation to permeability distribution, non-uniform wettability of matrix blocks can have a substantial impact on recovery during water injection cycles while recovery efficiency during the gas injection cycle can be reduced by a factor of 50%. Our work identifies the key factors that must be considered when modelling WAG floods in NFCR. We evaluate the reliability of conventional dual-porosity/dual- permeability numerical simulation approaches for NFCR by comparing results with multi-stage upscaled models through which we capture the fundamental controls on multi-phase flow. Hence, we can offer explanations for possible NFCR responses to WAG flooding and novel ways to improve the predictive ability of field-scale numerical simulation models.
Original languageEnglish
Title of host publicationSPE Reservoir Characterisation and Simulation Conference and Exhibition (RCSC 2013)
Subtitle of host publicationnew approaches in characterisation and modelling of complex reservoirs
Place of PublicationRichardson, Texas
PublisherSociety of Petroleum Engineers
Number of pages17
ISBN (Electronic)9781613992685
ISBN (Print)9781629931449
Publication statusPublished - Sept 2013
EventSPE Reservoir Characterisation and Simulation Conference and Exhibition 2013 - Abu Dhabi, United Arab Emirates
Duration: 16 Sept 201318 Sept 2013


ConferenceSPE Reservoir Characterisation and Simulation Conference and Exhibition 2013
Abbreviated titleRCSC 2013
Country/TerritoryUnited Arab Emirates
CityAbu Dhabi


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