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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Critical Factors of Carbonate Pore Systems - Implications for Reservoirs in the Middle East

Oliver Weidlich1; Stefan Lubeseder2; Klaus Flender1

(1) EOG/G, Wintershall Holding AG, Kassel, Germany.

(2) EV-Qatar, Wintershall Holding AG, Doha, Qatar.

Generating predictive models for reservoir quality distribution is challenging for carbonate reservoirs. Usually, quantitative porosity data for these models are exclusively derived from conventional core plug measurements or log data (log-derived effective porosity, RHOB, DT; NMR in rare cases).

For this study, conventional poro/perm plots from plugs and log data of Cretaceous and Jurassic carbonates were analysed using data from several wells offshore Qatar. The following observations are based on data from Kharaib, Yamama, Upper Sulaiy, Lower Sulaiy and Arab samples:

  1. Poro-perm plots of the above stratigraphic units show a significant overlap of data despite some minor trends
  2. Core plug porosity data do not decrease with depths.
  3. Cross plots of log-derived and core plug porosities show no trend, e.g. core plug porosities were higher, similar or lower than equivalent porosity log data (notably NPHI).

Our observations suggest that additional parameters need to be considered to improve reservoir models. The concept of reservoir rock types has been repeatedly regarded as an effective tool that integrates geologic observations with porosity and permeability data. We combine under consideration of sedimentologic and diagenetic factors conventional porosity data from plugs and logs with image analysis-based pore size, analysis from high-resolution core photos and thin sections. With this approach we established a six-fold reservoir rock type concept for the investigated Jurassic-Cretaceous carbonates to better characterize the variability of pore space and pore geometries of reservoirs units.