Advance Formation Evaluation of Kerogen Rich Reservoir - A Case Study from Kuwait

By

 Heyam .M Al-Ammar¹, Meshary.M Ameen², Ahmed El Sherif³, Moinuddin M. Qidwai²

(1) Kuwait Oil Company, Ahmadi, Kuwait (2) Kuwait Oil Company, Ahmadi, (3) Schlumberger, Ahmadi, Kuwait

 Standard approach of determining porosity from cross-plots of Neutron, Density and Sonic does not provide acceptable porosity in reservoirs having high kerogen content due to extremely high kerogen responses. Moreover, reasonably accurate estimation of Kerogen content in such reservoirs by conventional log analysis models is not possible as kerogen parameters are not precisely known.

Use of Nuclear Magnetic Resonance (NMR) derived porosity that is not affected by kerogen/immobile hydrocarbons has made it possible to evaluate such reservoirs quite accurately. Accuracy of these results has been verified by comparison with the core porosity corrected for reservoir conditions.

The difference in the cross-plots derived porosities and those from NMR reflect the kerogen content fairly well. A reasonable correlation has been observed between Uranium component of the radioactivity determined from Gamma Ray Spectrometry and the kerogen content in most parts of reservoir.

By comparison of NMR porosities integrated across different ranges of pore sizes were done with the core data and a reasonable match has been achieved. These porosities have been used in the final log interpretation.

Effective porosity of the reservoir is very low therefore the production depends mainly on fractures. Sonic Borehole Imager has been used as principle fracture indicating tool because of oil base mud. Comparison of fractures detected from Sonic Borehole Imager with NMR permeability and the results of Stoneley analysis enabled to identify open fractures, select perforations intervals precisely for successful completion of the wells.