Petrofacies Evolution of Bayana Basin Sandstones of Mesoproterozoic Delhi Supergroup, Bharatpur District, Rajasthan, Northwestern India

The paper embodies results of petrofacies, detrital mineralogy and textural aspects of Bayana Basin sandstones of the Delhi Supergroup. These sandstones consisting of various types of quartz, feldspar, mica, rock fragments and heavy minerals are medium to fine grained and moderately well sorted. These sediments are generally subangular to subrounded with low sphericity. Various factors responsible for modification of the original detrital composition of the sandstones have been critically examined. Distance of transport is one of the factors which control the composition at the time of deposition. The plots of petrofacies in QtnFnL, QmnFnLt, QpnLvnLs and QmnPnK ternary diagrams suggest mainly basement uplift source (Craton interior) in a rifted continental margin basin setting, which has also received sediment input from recycled orogen provenance.

The influence of bioturbation on sandy reservoirs: the delta front sand of the lower Zhujiang Formation, Baiyun Depression, Zhujiang River Mouth Basin

Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained:(1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies.(2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils.(3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir's physical property when sea level slowly rises and improves the reservoir's physical property when base level slowly falls.

Diagenetic and Reservoir Quality Variation of Miocene Sandstone Reservoir Analogues from Three Basins of Southern California,USA

The Miocene sandstone deposits in the Southern California region are important hydrocarbon reservoirs. However, their development has been very challenging due to the wide variability in their reservoir quality. These sandstones have been studied from three sedimentary basins by petrographic thin section, scanning electron microscope, and X-ray diffraction to evaluate and compare the influence of diagenesis on their reservoir quality in these basins. Four petrofacies, namely P1(sand injectite or dyke), P2(sub-marine fan), P3(turbidite and marine-influenced alluvial fans) and P4(continental sandstones) have been identified. P1 and P2 characterise the sandstones in the San Joaquin forearc basin and are affected by kaolinite and extensive early calcite diagenesis. P3 and P4 delineate the sandstones in the Cajon Valley and Salton Trough strike-slip basins and are dominated by smectite, mixed illite-smectite, early calcite and late calcite diagenesis. Early calcite cement in P3 and P4 is in lower proportion than in P1 and P2. Although the dissolution of these sandstones by acidic fluids did not have a pattern, it, however, has the most considerable influence on P2 creating moldic pores which are expected to increase pore connectivity. The relatively abundant dissolution pores in P2, together with the absence of late authigenic calcite and illite clay in comparison to the other petrofacies studied are likely to make this sandstone facies the best reservoir targets in the Southern California region. These rocks are analogous to producing reservoirs in the region. However, because, petroleum accumulation in these reservoirs are compartmentalized by early calcite cement, maximum recovery using acidified fluids is recommended to dissolve the calcite-filled pores in order to increase connectivity of their pore network and enhance flow potential.

Shoreline evolution and modern beach sand composition along a coastal stretch of the Tyrrhenian Sea, southern Italy

This contribution focuses on a multidisciplinary research showing the geomorphological evolution and the beach sand composition of the Tyrrhenian shoreline between Capo Suvero promontory and Gizzeria Lido village(Calabria,southern Italy). The aim of the geomorphological analysis was to reconstruct the evolutionary shoreline stages and the present-day sedimentary dynamics along approximately 6 km of coastline. The results show a general trend of beach nourishment during the period 1870–2019. In this period, the maximum shoreline accretion value was estimated equal to + 900 m with an average rate of + 6.5 m/yr. Moreover, although the general evolutionary trend is characterized by a remarkable accretion, the geomorphological analysis highlighted continuous modifications of the beaches including erosion processes. The continuous beach modifications occurred mainly between 1953 and1983 and were caused mainly by human activity in the coastal areas and inside the hydrographic basins. The beach sand composition allowed an assessment of the mainland petrological sedimentary province and its dispersal pattern of the present coastal dynamics. Petrographic analysis of beach sands identified a lithic metamorphi-clastic petrofacies, characterized by abundant fine-grained schists and phyllites sourced from the crystalline terrains of the Coastal Range front and carried by the Savuto River. The sand is also composed of a mineral assemblage comparable to that of the Amato River provenance. In terms of framework detrital constituents of QFL(quartz:feldspars:aphanitic lithic fragments) and of essential extraclasts, such as granitoid:sedimentary:metamorphic phaneritic rock fragments(Rg:Rs:Rm), sand maturity changes moderately from backshore to shoreface, suggesting that transport processes had a little effect on sand maturity. Moreover, the modal composition suggests that the Capo Suvero promontory does not obstruct longshore sand transport from the north. Indeed, sands displaced by currents driven by storm-wave activity bypass this rocky headland.