Naslov
Palaeosoils stacking patterns as a tool for unravelling the subsurface architecture of mud- rich fluvial reservoirs

Autori
Moscariello, A ; Šegvić, Branimir

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
12th Swiss Geoscience Meeting

Mjesto i datum
Fribourg, Švicarska, 21.11.2014. - 22.11.2014

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
no ; key ; words

Sažetak
In the subsurface, robust well correlation represents the starting point in order to understand the architectural framework of any reservoirs rock. Especially in mud-rich continental barren sequences, characterised by scarce occurrence of sandstone beds, correlation may result a difficult task. In this type of depositional environment correlation techniques based on bio- or chemo- stratigraphic analyses have been successfully applied to identify discrete chronostratigraphic units which generally may represent 3rd or 4th order stratigraphic changes in response to either tectonic (e.g. increased erosion and sediment supply, changes in provenance) or climatic changes (e.g. weathering processes in the catchment, changes in erosion and sediment supply) or, in most cases, both. Yet, when sand bodies in the subsurface are thought to be narrower than the actual well spacing, the correlation between them is becoming a challenge and more detailed information are then required to outline better the internal reservoir architecture and identify channel distribution. Detailed insights on reservoir anatomy have been provided by the study of palaeosols. Their different types (pedofacies) and vertical trends can directly be related to different aggradation rates and in turn proximity to channel belt. Ultimately this can provide useful information on the overall stratigraphic pattern and sand connectivity within the fluvial reservoir. Different pedofacies signatures, as a function of their maturity (e.g peds development, rootlets and nodules distribution, degree of preservation of primary sedimentary structures) can be identified both on core and logs and a different range of pedofacies types can be identified (usually 2 to 4). Pedofacies composition highlighted by both standard petrographic microscopy and QEMSCAN automated mineralogy reflects the time of subaerial exposure and the pedologic processes (bioturbation and mineralisation) occurred during the soil formation. The presence of different stage of maturity in paleosoils can be also highlighted by shear sonic logs which may respond to the different degree of vertical discontinuities in the rock associated with paleosoils development (peds). In general a highly mature paleosoils suggest very low aggradation rates of new sediments and hence a large distance from active channel belts or a temporary stop/decrease in sediment supply (e.g. no overbank deposition due to dry period or reduced water discharge). The staking pattern of these pedofacies can therefore unravel the avulsive and aggradational character of a river system. The study of several wells in a study area can unravel lateral changes in fluvial aggradational style within each chronostratigraphic zone (based on bio or chemo-stratigraphy) and therefore indicate large scale architectural changes at reservoir scale. The systematic mineralogical study of these pedofacies, with automated mineralogical techniques can help to unravel important changes in provenance or autogenic components throughout the stratigraphic record and thus help discriminating the tectonic vs. climatic signature recorded by the sedimentary succession.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA