Critical factors of carbonate pore systems: Implications for reservoirs in the Middle East. 9th Middle East Geosciences Conference, GEO 2010.

Abstract

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, bulk density, interval transit time, and nuclear magnetic resonance in rare cases). For this study, conventional porosity-permeability plots from plugs and log data of Cretaceous and Jurassic carbonates were analysed using data from several offshore wells in Qatar. The following observations are based on data from Kharaib, Yamama, Upper Sulaiy, Lower Sulaiy and Arab samples: (1) Porosity-permeabilty 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 depth. (3) Cross plots of log-derived and core-plug porosities show no trend; for example core-plug porosities were higher, similar or lower than equivalent porosity log data (notably neutron pososity). 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 reservoir units.