Exploring for Fan and Delta Sandstones in the Offshore Falklands Basins

Abstract

Four basins surround the Falkland Islands, but only the North Falkland Basin has been drilled; six wells were drilled there in 1998. Although all six wells encountered good quality sandstones, none of them targeted the basin margins, on what are now thought to be the optimum migration pathways associated with the basin's thick lacustrine source rocks. Subsequently, a 3D seismic survey acquired in 2004 was designed to identify potential basin-margin -derived sandstones entering the basin along transfer zones. From this survey, a number of basin-margin -attached fans have been identified; these prograded into lacustrine waters of varying depths. These Early Cretaceous alluvial/fan delta/deep-lacustrine fan systems are interpreted to provide excellent potential reservoir facies as they are intimately associated with thick, mature source rocks. They will provide the focus for the next planned phase of exploration in the North Falkland Basin.A phase of drilling is also planned for the basins to the south of the Islands, where large deltaic and fan systems, slightly younger than those imaged in the North Falkland Basin, are seen on seismic to prograde from the same Palaeozoic hinterland that produced the older, North Falkland Basin fans.This paper attempts to show how sedimentary models derived from targeted seismic programmes following initial exploration can be utilised to plan and improve new drilling campaigns in a frontier basin. It presents an analysis of sediment dispersal patterns in basins of marine and lacustrine origin linked to a single hinterland area, and highlights the nature of the relationship between relay ramp/transfer zone development and sediment dispersal patterns in the subsurface.

Integrated biostratigraphy and chemical stratigraphy in the development of a reservoir-scale stratigraphic framework for the Sea Lion Field area, North Falkland Basin

“…It is only with the recent radiometric data summarized here that provides a younger Early Aptian age for the upper age limit of these sandstones, and therefore recalibrates the C. rallus event to a younger, Aptian age. In all other respects, the findings of this paper and others in 'The North Falkland Basin revisited' thematic set build upon and complement the depositional model described by Richards et al (2006).…”

“…Richards et al (2006) suggested that the majority of the coarse clastic input (therefore including the SLMC) into the NFB occurred during the Berriasian-Barremian. Similarly, the biostratigraphic data presented here would also date these sandstones as predominantly not younger than Barremian, based on the C. rallus event described above.…”

A First Approach to Assess the Impact of Bottom Trawling Over Vulnerable Marine Ecosystems on the High Seas of the Southwest Atlantic

“…The middle slope surveyed was entrenched by seven submarine canyons [78]. Pockmarks and other seismic and morphologic evidence of gas/fluids seepage were pervasive throughout the entire survey area and more intense in the southern middle part [80]. Water coral communities associated with those pockmarks could be quite extensive in the study area.…”

“…These gas and fluid seepages contributed to the formation of canyons and to the partial detachment of blocks from the canyon walls. Thus, the thermogenic gas responsible for the formation of the identified pockmarks on the middle slope could be deep-seated, probably related to the Falkland Rift Basin, north of the Falkland (Malvinas) Islands [80,81]. The association of gas seepage with deep-water corals has been reported by [82] in pockmarks off Brazil.…”

Distribution of hydrocarbon leakage indicators in the Malvinas Basin, offshore Argentine continental margin

“…Until now, five wells found non-43 commercial hydrocarbon shows and only one gas chimney has been reported in this basin, 44 identified by the observation of a diffuse, vertical cone-shaped area in 2D seismic reflection 45 data (Richards et al, 2006). In contrast, within the neighbouring Austral-Magallanes Basin, 46 Thomas (1949) reported the occurrence of numerous gas seeps and one oil seep.…”