How depositional properties dictate the early diagenetic pathways and reservoir quality of sandstones?

The porosity and permeability (pore-scale attributes) of a host rock are the two important parameters for a consideration of a hydrocarbon reservoir. Often, these parameters determine the economic value, appraisal approaches and development plans for a hydrocarbon field. Although there are vast amount of individual studies on pore-scale reservoir quality controls of particular fields/formations, overview approaches towards the pre-exploration predictability is limited.

The pore-scale reservoir quality controls are typically investigated in two sub categories as (i) depositional and (ii) diagenetic controls, however, in most cases, these two factors act together to determine the final pore-scale attributes of a reservoir. Particularly in the clastic reservoirs, early diagenetic pathways are strongly linked to the depositional properties including 1) texture (grain-size, sorting and detrital clay content), 2) detrital composition (including detrital clay types), 3) fabric (sedimentary structures) and 4) original pore water composition, as these factors determine the fluid flow pathways and available elements in the relatively closed system. Although the sedimentology and diagenesis of clastic reservoirs and widely studied, these two topics are often handed in complete isolation with different research groups.

This proposal aims fill the gap between large-scale sedimentology with pore-scale data in order to form a complete understanding of early days/times of a sandstone reservoir. The study will focus on the lateral and vertical variations of the depositional properties of coastal/paralic systems and possible early diagenetic pathways in the context of sedimentary processes. The coastal depositional setting have particularly selected here, as it is often linked to the porosity preserving early diagenetic chlorite formation. Two study areas are planned to be used in order to form the link between micro and macro-word; 1) well-exposed and intensely-studied Cretaceous deltaic successions in Utah (USA), and 2) Holocene cores from Ravenglass Estuary (UK). Studying the modern and ancient systems together will additionally allow to investigate the effects of compaction on depositional properties. Main tasks will include;
- Field work to build the sedimentological background for the study, including core and outcrop logging, correlation, process interpretation and sampling
- Sandstone petrography, XRD and SEM studies to define textural properties, grain composition, detrital clay types and diagenetic phases.
- In Ravenglass Estuary; pore water sampling in order to characterise possible original pore-water chemistry in various facies associations throughout the estuary.