Reservoir characterization and modeling of a tight lower Cretaceous carbonate, Abu Dhabi, United Arab Emirates

  • Aala Awad Idriss Mohamed

Student thesis: Master's Thesis

Abstract

This research aims to build a proper workflow to characterize tight carbonate reservoirs. The characterization will be based on reservoir rock typing using petrography, Mercury Injection capillary pressure (MICP), Nuclear Magnetic Resonance (NMR) and Dual Energy Computed Tomography (DE CT) on reservoir samples from Abu Dhabi field. Reservoir rock typing is essential for characterizing the heterogeneity of carbonate rocks. With DE CT we were able to visualize and characterize the heterogeneity of several plug samples. MICP and NMR tests further enhanced our understanding on the pore geometry and connectivity which had a bearing on the capillary pressure behaviour of these rocks. As a result of these investigations, we were able to group the rocks into different petrophysical groups (rock types) and generate their respective saturation models. These models will be used in subsequent fluid flow simulation studies. Also, the NMR data, coupled with core analysis information, allowed us to fine-tune existing NMR-permeability models, which could be used in future development wells. The deliverables of this research have direct application in future static and dynamic models of the reservoir. As part of this research we also built a 3D geological model (small sector), which will be used in subsequent EOR studies. This model honors the reservoir cyclicity, the depositional facies and diagenetic features detected during our petrographic observations. The carbonate cycles were populated with porosities and permeabilities derived from core analysis information. Thin sections, SEM imaging Isotopes analysis and Image Porosity estimation were the main methods used to characterize the reservoir depositional facies, diagenetic features and how it affects the reservoir quality. We observed that in tight carbonate reservoir, the correlation between porosity and permeability is quite better than in porous and permeable carbonate systems. This has to do with the high diversity (variance) of pore systems in high porosity-high permeability carbonates. Understanding the initial depositional texture and the subsequent diagenetic overprint was crucial to link the geological facies with the rock fabric (pore size distributions and pore throat size distributions). In this research we used 65 horizontal plugs from Bab equivalent of Thamama Group, characterized by mudstones and wackestones and micritization as the dominant diagenetic process. All of these samples were subjected to in-house petrographic observations, MICP test done by external laboratory, in-house NMR measurements and dual energy scanning by external laboratory. Our aim was to analyse, interpret and integrate all results in a consistent and coherent manner so that proper rock-typing could be established, not only for the direct input into the 3D geological model but also as an input for the planned core flooding experiments as part of an ongoing EOR research project. The tightness of this reservoir was confirmed by NMR results indicating narrow pore-size distributions (shorter T2 means) with dominant micro-pores. MICP results also showed the majority of the samples with pore-throats of less than 0.5 microns. The laboratory NMR-MICP data, when integrated with open-hole log and conventional core-analysis data showed a good agreement. The full integration of the data led to a complete understanding of the spatial and vertical heterogeneity of this tight reservoir.
Date of Award2014
Original languageAmerican English
SupervisorJorge Salgado Gomes (Supervisor)

Keywords

  • Earth sciences
  • Petroleum Geology
  • Sedimentary Geology
  • 0583:Petroleum Geology
  • 0594:Sedimentary Geology

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