Uncertainty and Sensitivity Analysis on Clastic Systems: Integrated Workflows for Understanding and Managing the Risk, A Case Study in Tuwayil Formation UAE

This study has been done on Late Cretaceous tight clastic reservoir located south west of Abu Dhabi city with the border with Saudi Arabia. The field was discovered in the 1960s and a few wells were drilled subsequently. The Tuwyail clastic reservoir is characterized as tight with average permeability below 1 mD. The trap is identified as structural trap as north south anticline with gentle dip in both sides. Total of six wells were drilled targeting Tuwyail reservoir which part is of Wasia group. However, assessing potential of this accumulation poses a great challenge not only in terms of understanding of the depositional system which still unknown before but also in terms of quality of the legacy data like well data that impact the modeling studies. The aim of this paper is to provide an insight on integrated workflows for assessing the different uncertainties on clastic systems with limited data, focused on the most important sensitivities parameters impacting the oil in place, like reservoir proportions, free water level [FWL] and lateral distributions of the sedimentary elements within the area of interest which playing a big rules in future developing of the field. Before moving to full field development a full uncertainty and sensitivity analyses were conducted for the Tuwayil reservoir to find the highly uncertain parameters that impacting the future development of the reservoir, in the same time the main challenges is the limited data with low quality as the wells had been drilled in 60s with limited technology at that time and the core data were left in a bad conditions since the filed was left behind.

Depositional Heterogeneities and Brittleness of Mudstone Lithofacies in the Marcellus Subgroup, Appalachian Basin, New York, U.S.A.

Organic-rich rocks of the Marcellus subgroup in the study area consist of a diverse suite of mudstone lithofacies that were deposited in distinct facies belts. Lithofacies in the succession range in composition from argillaceous to siliceous, calcareous, and carbonaceous mudstone. Heterogeneities in the succession occurs in the form of varying mineralogical composition, slightly bioturbated to highly bioturbated chaotic matrix, organic-rich and organic-lean laminae, scattered fossil shells in the matrix, and fossils acting as lamination planes. Lithofacies were deposited in three facies belts from the proximal to the distal zone of the depositional system. Bedded siliceous mudstone (BSM) facies occur in the proximal facies belt and consists of a high quartz content in addition to clay minerals and pyrite. In the medial part of the facies belt lies the laminated argillaceous mudstone (LAM), bedded calcareous mudstone (BCaM), and bedded carbonaceous mudstone (BCM). The size of detrital mineral grains in the lithofacies of the medial facies belt is larger than bedded argillaceous mudstone (BAM) of the distal facies belt, characterized by clay-rich matrix with occasional fossil shells and horizontally aligned fossils. Two types of horizontal traces and one type of fecal string characterize the proximal mud-stone facies, whereas only single horizontal trace fossil is found in the mudstones of the medial and distal facies belt. Parallel alignment of fossil shells and fossil lags in lithofacies indicate that bed-load transport was active periodically from the proximal source of the depositional system. Bioturbation has heavily affected all of the lithofacies and presence of mottled burrows as well as Devonian fauna indicate that oxic to dysoxic conditions prevailed during deposition. The deposition of this organic-rich mudstone succession through dynamic processes in an overall oxic to dysoxic environment is different from conventional anoxic depositional models interpreted for most of the organic rich black shales worldwide. Total organic content (TOC) varies from top to bottom in the succession and is highest in BCM facies. The brittleness index, calculated on the basis of mineralogy, allowed classification of the lithofacies into three distinct zones, i.e., a brittle zone, a less brittle zone, and a ductile zone with a general proximal to distal decrease in the brittle behavior due to a decrease in the size of the sediments.

Lateral migration of large sedimentary bodies in a deep-marine system offshore of Argentina

Contourite features are increasingly identified in seismic data, but the mechanisms controlling their evolution remain poorly understood. Using 2D multichannel reflection seismic and well data, this study describes large Oligocene- to middle Miocene-aged sedimentary bodies that show prominent lateral migration along the base of the Argentine slope. These form part of a contourite depositional system with four morphological elements: a plastered drift, a contourite channel, an asymmetric mounded drift, and an erosive surface. The features appear within four seismic units (SU1–SU4) bounded by discontinuities. Their sedimentary stacking patterns indicate three evolutionary stages: an onset stage (I) (~ 34–25 Ma), a growth stage (II) (~ 25–14 Ma), and (III) a burial stage (< 14 Ma). The system reveals that lateral migration of large sedimentary bodies is not only confined to shallow or littoral marine environments and demonstrates how bottom currents and secondary oceanographic processes influence contourite morphologies. Two cores of a single water mass, in this case, the Antarctic Bottom Water and its upper interface, may drive upslope migration of asymmetric mounded drifts. Seismic images also show evidence of recirculating bottom currents which have modulated the system’s evolution. Elucidation of these novel processes will enhance basin analysis and palaeoceanographic reconstructions.

Basin-scale Paleoecology: Using Semi-quantitative Analysis of the Ichnofabric within Kutai Basin (Indonesia)

Ichnofossils are still not used in paleoecological studies, even though they are a valuable proxy for paleoecology. This study focused on a semi-quantitative approach to a number of ichnofabric variables, i.e. ichnofossil association, bioturbation index (BI), ichnodiversity (ID), number of behaviors (NB), penetration depth (PD), and burrow diameter (DM). It was proved that the scores of those variables were low to medium because of the paleoecological fluvial-marine transition depositional processes in the Serravallian-Tortonian interval in Kutai Basin, Indonesia. This paper contributes an ichnofabric model that is visualized as histograms. One histogram shows the most common ichnofossil associations found in ichnofabric units, i.e., Ophiomorpha, Skolithos, Paleophycus, Planolites, Thalassinoides, and Chondrites. The other histograms describe the ichnofabric variables scores for BI, ID, NB, PD, and DM. The variables represent low to medium scores, a characteristic of a brackish paleoecology at basin-scale, a unique indicator for the fluvial-marine transition depositional system.

Chronology of recent sedimentary infill of the Inner Río de la Plata Estuary, Argentina

The Inner Río de la Plata Estuary is a sedimentary depositional system that resulted from fluvial-deltaic activity. Gentle Pliocene–Pleistocene slopes make-up the northern side of the estuary whereas small cliffs of the same age constitute the southern side. A long coastal estuarine barrier developed at about 6000 years BP when the maximum flooding surface occurred. Attached to this barrier, and at a lower elevation, is a large strandplain (covering an area of about 2400 km2) which displays more than 220 beach ridges. In different areas, the dating indicates a periodicity of 13.4–13.7 years for the development of each beach ridge. These data are like the periodicity of the ENSO effects, which could be associated with the variability of Sunspots. These ridges were formed shortly after the maximum flooding surface, which was followed by a gradual fall in sea-level that contributed significantly to the Inner Río de la Plata Estuary sedimentary infill. In addition, ENSO activities were probably instrumental in the distribution of the main geoforms in the Inner Rio de la Plata Estuary. Small deltas, which were generated by other rivers and creeks such as the Nogoyá Arroyo and the Gualeguay River, developed coevally with the coastal estuarine barrier. The Ibicuy Delta grew in the middle of the inner Río de la Plata Estuary when the former Paraná River flowed northwards during the sea-level fall. The upper part of the delta front was reworked, giving rise to a large dunefield. Thereafter, a chenier plain developed along with tidal flats. The current Paraná Delta continues to prograde at a rate of about 56–64 m/year (m year−1). The sedimentary infill of the Inner Río de la Plata Estuary occurred along the Holocene.