The sandstone units of the Early Cretaceous Lower Goru Formation are significant reservoir for gas, oil, and condensates in the Lower Indus Basin of Pakistan. Even though these sandstones are significant reservoir rocks for hydrocarbon exploration, the diagenetic controls on the reservoir properties of the sandstones are poorly documented. For effective exploration, production, and appraisal of a promising reservoir, the diagenesis and reservoir properties must be comprehensively analyzed first. For this study, core samples from depths of more than 3100 m from the KD-01 well within the central division of the basin have been studied. These sandstones were analyzed using petrographic, X-ray diffraction, and scanning electron microscopic analyses to unravel diagenetic impacts on reservoir properties of the sandstone. Medium to coarse-grained and well-sorted sandstone have been identified during petrographic study. The sandstone are categorized as arkose and lithic arkose. Principal diagenetic events which have resulted in changing the primary characters of the sandstones are compaction, cementation, dissolution, and mineral replacement. The observed diagenetic processes can be grouped into early, burial, and late diagenesis. Chlorite is the dominant diagenetic constituent that occurs as rims, coatings, and replacing grains. The early phase of coating of authigenic chlorite has preserved the primary porosity. The recrystallization of chlorite into chamosite has massively reduced the original pore space because of its bridging structure. The current study reveals that diagenetic processes have altered the original rock properties and reservoir characteristics of the Lower Goru sandstone. These preliminary outcomes of this study have great potential to improve the understanding of diagenetic process and their impact on reservoir properties of the Lower Goru sandstone in the Lower Indus Basin and adjoining areas.

Numerous moundy reflections were found at the Upper Meishan Formation in southern Qiongdongnan Basin, South China Sea which are suspected reefs. However, no common understanding on the seismic and geologic interpretation was acquired. Based on seismic reflection identification, geometrical configuration description, wave impedance inversion, forward simulation, analysis of reef-building sedimentary environments and pseudomorph identification, these suspected-reef moundy reflections were studied in details. Three types of reefs were recognized, i.e., patch reef, platform-edge reef, and pinnacle reef. They have some typical characteristics of reefs, including moundy or lenticular shape, clear outline with crest and canal, internal foreset bedding, bidirectional uplap between limbs, and strong reflection at top and bottom. The patch reefs are of moundy seismic facies, with moderate–strong amplitude and moderate frequency, and distribute at the higher part of southern slope belt. Fore-reef and back-reef of patch reefs are slightly asymmetrical being perpendicular to palaeo-bathymetric orientation; while symmetrical to slightly asymmetrical being parallel to the palaeo-bathymetric orientation, and the wave impedance value is about 7 kg/m3×m/s. Platform-edge reefs are of flat-moundy seismic facies with strong amplitude and moderate frequency, which develop at the carbonate platform edge of higher part of southern slope belt, and the wave impedance value is about 7.5 kg/m3×m/s. Pinnacle reefs grow up on volcanic cones, forming the complex of pinnacle reef and volcanic cone. The Miocene Meishan Formation reefs in southern Qiongdongnan Basin, northern South China Sea, with high quality source–reservoir–seal assemblages, have good petroleum exploration prospects

The Upper Ordovician Midale field is located in the northern Williston basin in southeast Saskatchewan, Canada. Hydrocarbons are hosted mainly in the dolomite reservoirs with burrowed textures in the upper Yeoman Formation. These reservoirs are characterized by intercrystalline porosity in the dolomitized matrix, with variable amounts of vugs and fractures, and can be divided into four zones. Reservoir zones 1 and 2, typically 6–10 m (20–33 ft) thick in total, are situated in the upper part of the traps and commonly bear oil. Although the underlying zones 3 and 4 are thicker, they commonly contain only water because they are located below the spillpoint of the hydrocarbon traps. The seismic reflection of the Red River reservoirs in the Midale field is characterized by a weak- to medium-amplitude trough immediately above the positive reflection of the Winnipeg shale. Where all four zones are present, an additional peak occurs on the seismic profile above the original reservoir reflection. This additional peak, however, disappears where reservoir zones 3 and 4 pinch out. Where there is an increase in the thickness of reservoir zones 1 and 2 or amalgamation of zone 1 with zone 2, the Red River reservoirs are characterized by high-amplitude and high-frequency reflections on seismic profiles. The Ordovician oil pools in the Midale area are associated with low-relief anticline structures. These low-relief structures are interpreted as the compactional drape of Red River strata over local Precambrian basement highs. The source of hydrocarbons in the Red River reservoirs is Ordovician kukersites. A wide range of API fractions for the oils from the Midale pools suggests a mixing of low-maturity oils, sourced from local kukersite beds, and high-maturity oils that migrated over a long distance from the south. The hydrocarbon production from Red River Midale pools is characterized by the fast rise of water cut and high water output, which can be attributed to the small pool size and the fracture systems connecting oil and water zones.