Reservoir characterization of the Lower Abu Madi Formation using core analysis data: El-Wastani gas field, Egypt

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The Messinian (Upper Miocene) sandstones of the Lower Abu Madi unit are the main reservoirs of the El-Wastani (EW) gas field, located in the onshore Nile Delta of Egypt. Reservoir quality is highly variable and represents the major risk in locating new delineation and development wells in the field. Four lithofacies (F1, F2, F3 and F4) are characterized based on textural attributes and sedimentary structures. Facies F4, which is a medium to coarse-grained fluvial channel sandstone, exhibits the best reservoir rock quality. Four hydraulic flow units (HFU 1 through HFU 4) were delineated in the studied wells with flow zone index (FZI) values indicative of a broad range of hydraulic properties. The cementation factor (m) value, was calculated from the inverse relationship between porosity and formation factor for EW-4 and EW-6 wells, agrees with the published values of clean sandstone reservoirs. The results of grain density analyses is close to the published value of grain density of quartz, and also supported by the results of petrographic study, where quartz is the dominant framework mineral. Generally, both the permeability and porosity can be linked to the two derived electrical properties (formation resistivity factor and electrical tortuosity) in the clastic reservoirs of the Lower Abu Madi unit. This correlation is particularly evident in the western and central parts of the study area at EW-4 and EW-6 wells, where facies F4 is dominant.