A proposed classification for the reservoir quality assessment of hydrocarbon-bearing sandstone and carbonate reservoirs: A correlative study based on different assessment petrophysical procedures

Petrophysical reservoir quality assessment is achieved through several methods based on the pore volume, connectivity, and conductivity. Reservoir quality index (RQI), and reservoir flow indicator (FZI) are among the most important parameters that are used for this assessment. In addition, the effective pore radius of Winland (r35) is additional technique that is applied based on mercury injection capillary pressure plots (MICP). For the present study, a total of 185 sandstone and 64 carbonate plug samples were collected from different oil and gas fields, in addition to some surface analogs in the Gulf of Suez and Nile Delta of Egypt. The effective porosity, matrix gas permeability and the reservoir quality parameters, including the RQI and FZI were measured. Based on their mineral composition and petrophysical behavior, the studied samples are summed up into six petrophysical static rock types (PSRTs) of different ranks, Including tight, poor, fair, good, very good, and excellent rock types. In addition, MICP data is available for 40 sandstone and 19 carbonate samples from the same gas and oil fields. The MICP results indicate that, the pore sizes can be classified into mega, macro, meso, micro, and nano pores. Integration between the capillary curves and the pore sizes enables accurate assessment of the reservoir quality. The present study aims to correlate between the reservoir ranks that is obtained from the MICP tests and that obtained from Winland equation, RQI, and FZI values. the other reservoir quality parameters are applicable for both sandstone and carbonate reservoirs. The variation of the reservoir quality rank based on the applied technique regardless of its interstitial filling fluids indicates the needs to a new ranking classification. The present study introduces a new ranking classification which is based on the cutoff values for each reservoir. So, it takes type of the saturating fluids into consideration, and it is applicable for all reservoirs including the conventional, unconventional tight reservoirs, and fractured reservoirs.

Automated summary

Petrophysical reservoir quality assessment involves parameters such as RQI, FZI, and MICP for sandstone and carbonate rocks. The study classified samples into six petrophysical static rock types and introduced a new ranking classification based on cutoff values for all reservoir types. The MICP results showed various pore sizes and the need for a new ranking system irrespective of filling fluids.