Pore fabric assignment using electrical conductivity of some Albian–Cenomanian sequences in north Eastern Desert, Egypt

Abstract

The electric pore fabric concept has been testified in many previous studies, mostly concerned with sandstone rock samples. The present study is a further trial to testify the reliability of the proposed concept on carbonate and clastic facies. The studied facies are representative for the AlbianCenomanian Raha and Abu Qada Formations at the western side of the Gulf of Suez in Egypt. A total of 37 samples have been studied petrophysically by measuring electric conductivity in 3-D to rank their petrophysical potentiality and to detect their electric pore fabric. The studied samples are grouped into four facies, namely: (1) facies 1 (calcareous sandy siltstones) and (2) facies 4 (glauconitic quartz arenite) as clastic facies as well as (3) facies 2 (bioclastic limestones, and dolostones) and (4) facies 3 (clayey to sandy limestones) as carbonate facies. Porosity values of the studied carbonate facies are very good due to dolomitization and dissolution, whereas porosity values of the clastic facies are poor due to their high clay content. The formation resistivity factor values are low to medium values due to the reducing effect of the clay content and the very good porosity values. Archie's parameters a and m are mostly related to the formation resistivity factor and to some extent to the mineralogical composition as well as the electric tortuosity. The electric pore fabrics of the studied facies are slightly anisotropic, mostly as primary depositional fabrics affected by slight foliation rather than lineation. Presence of a slight fracturing system can be revealed by assigning the minimum formation resistivity factor through the vertical direction perpendicular to the bedding plain. However, the fracturing system is still not strong enough to affect the electric pore anisotropy by increasing the electric pore lineation as a secondary fabrics' indicator.

Impacts of microfacies type on reservoir quality and pore fabric anisotropy of the Nubia sandstone in the central Eastern Desert, Egypt

“…However, impacts of the iron oxides and clay content on Archie's parameters are compensated by the highly porous and permeable nature of the studied Nubia sandstone which supports the connectivity of the interstitial pore spaces. It is noticed that the lithology factor (a) increases by decreasing the porosity exponent (m) as stated by Nabawy et al ().…”

“…A full description of the applied techniques was discussed by Nabawy et al (). For measuring permeability and assigning the hydraulic pore fabric, three perpendicular plugs per each block sample have been drilled in the vertical direction perpendicular to the bedding plane (one sample) and in the horizontal direction referring to the N‐S and E‐W directions (two samples).…”

“…The pore fabric assignment of the Nubia sandstone using their magnetic susceptibility, permeability, thermal, and acoustic properties has been studied extensively by Nabawy et al () and Nabawy and Géraud (). It simulates the pore space as a pore ellipsoid of dimensions relative to its real dimensions.…”

“…It contains some erratically scattered quartz pebbles and gravels that seem to be transferred from the precursor great Sahara glaciers of the Late Ordovician–Early Silurian age which extended over vast regional areas in the north‐western parts of Africa (Caputo & Crowell, ; Issawi & Jux, ; Nabawy et al, 2019b). Sedimentology, petrophysical properties, geologic and structural setting, and reservoir quality of the Nubia sandstone have been studied extensively by many authors in the Eastern Desert (Kassab et al, ; Nabawy & David, ; Nabawy et al, 2019b), south Egypt (Nabawy & Géraud, ; Nabawy, Sediek, & Nafee, ), the Gulf of Suez (El Sharawy & Nabawy, , ; El‐Gendy, Barakat, & Abdallah, ), and Sinai (David et al, ; Nabawy & David, ).…”

“…The magnetic pore fabric has the advantage of the ability to introduce a precise estimate of inclination and declination of pore spaces extensions in 3‐D, according to the magnetic north (Hamilton & Rees, ; Pfleiderer & Kissel, ; Tarling & Hrouda, ). On the other side, the hydraulic and electric pore fabrics which can be assigned by measuring permeability and electric conductivity for three perpendicular plugs (oriented vertically to the bedding plane and horizontally parallel to the bedding plane to N‐S and E‐W) can introduce a more reliable estimate on anisotropy of the pore conductivity which is mostly controlled by the pore throat size rather than the pore volume (Nabawy et al, , 2019b; Serra, ).…”