الملخص الإنجليزي
With the shift in hydrocarbon exploration, there is a greater emphasis on complex, deep,
unconventional reservoirs than conventional reservoirs. This change highlights the
importance of comprehending how the depositional environment and diagenetic
processes that are influenced by factors such as temperature, pressure, and depth
impact the quality of the reservoir and the properties of the rock.
This study aims to discuss clay minerals’ origin, distribution, and their control on the
quality of the marine-influenced Miqrat Sandstone reservoir formation from the Huqf
Outcrop. The objectives were approached using qualitative and quantitative analysis
such as the petrographical optical microscope, point counting data, scanning electron
microscope (SEM), and the SEM equipped with dispersed energy spectrometer (EDS), Xray diffraction (XRD), X-ray fluorescence (XRF), QEMSCAN system, and the Petrog
software. All the methods provide detailed patterns of the variability and the extent of
clay coat analysis on the origin and the effect on Miqrat sandstone marine-dominated
sediments. The samples in this study were collected from the Huqf outcrop from three
measured sections in Central Oman.
The analyses reveal the abundance presence of kaolinite minerals in the Miqrat
Formation that predominantly resulted from eodiagenesis mechanically infiltrated mud
matrix into the intertidal and subtidal sandstone facies, triggered by the tidal forces,
which led to the precipitation of kaolinite clay minerals. Kaolinites are displayed as a
booklet shape pore-filling the sandstone grains and occluding the pore spaces. Kaolinite
clay minerals have undergone a diagenetic process during mesodiagenesis and form clay
coats covering the surfaces of the detrital grains. The fibrous hair-like illite clays have
developed in some of the analyzed samples, which appear to be transformed from
kaolinite claysthrough the illitization process in the presence of𝐾
+and by the dissolution
of feldspar and mica grains. The kaolinite and illite minerals are found to coat the quartz
and feldspar grains of the Miqrat Sandstone. This results in the preservation of the
porosity in the system by preventing the formation of quartz overgrowths, which
severely destroy the reservoir quality. The effectiveness of preventing further silica
cementation directly depends on the thickness of the clay rims covering the detrital grain
surfaces and the percentage of coverage; either partly or completely.
This study may serve as an analog for other similar reservoir depositional settings and
conditions to investigate the origin and effect of grain-coating clay minerals in enhancing
reservoir quality and preventing the precipitation of silica overgrowth.
