Role of cementation and compaction in controlling the reservoir quality of the Middle to Late Jurassic Sandstones, Jara dome, Kachchh Basin, western India

Thin-section petrography, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses are applied to investigate the various diagenetic controls on the reservoir quality of the Ridge and Athleta Sandstone members (Chari Formation) of the Jara dome, Kachchh Basin, western India. The results show that the sandstones of Jara dome are quartz-arenite to sub-arkose, medium- to coarse-grained, sub-angular to sub-rounded, poorly to moderately well-sorted and having low- to medium-sphericity. Diagenetic features such as mechanical compaction, pressure solution, cementation, and dissolution of unstable framework grains are analysed to synthesize the reservoir characteristics. The principal cementing materials are carbonates, iron oxides, silica overgrowth, and authigenic clays, mainly chlorite and kaolinite. Compaction and cementation are the controlling factors for the reduction in porosity and permeability of the sandstones. Dissolution of detrital feldspars is the main cause of porosity enhancement in these sandstones. The relationship between the intergranular volume (IGV) and cement volume indicates that cementation had played a more important role in the destruction of primary porosity than that of compaction. On the one hand, the ubiquitous development of carbonate cement advocates the loss in primary porosity at the early stage of diagenesis, while on the other hand it also prevented the further compaction of sandstone, thus preserving unfilled voids as primary porosity. Precipitation of carbonate cement is followed by development of pore-lining and pore-filling clayey cements. The pore-filling kaolinite resulted in a considerable loss of porosity while the pore-lining chlorite has helped in retaining the porosity by preventing syntaxial silica overgrowths. The reservoir quality of the studied sandstone is reduced by the authigenic clay cements, early carbonate precipitation and silica overgrowths, nonetheless, it is improved by the dissolution and alteration of unstable grains, in addition to partial dissolution of carbonate cements. The potential of the studied sandstone to act as a reservoir is strongly related to sandstone diagenesis.

Automated summary

Thin-section petrography, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were used to investigate the diagenetic controls on the reservoir quality of the Ridge and Athleta Sandstone members in the Jara dome, Kachchh Basin, western India. The study found that carbonates, iron oxides, silica overgrowth, and authigenic clays like chlorite and kaolinite are the principal cementing materials in the sandstones. The reservoir quality of the sandstone is influenced by compaction, cementation, dissolution of unstable grains, and the precipitation of carbonate cement and silica overgrowths.