Sediment tracking (or provenance analysis) is a key tool in petroleum exploration and has proven especially useful in frontier basins. The traditional aim of provenance analysis is to identify the source of sediment or sedimentary rock deposited in a basin by directly linking a signal (petrographic or geochemical) in detrital grains with signals from rocks in a modern hinterland. By adopting this overly-simple approach, many additional insights, which may have important implications for the economic resource potential of a sedimentary rock, are overlooked. For example, conventional approaches can fail to reconcile or identify factors such as prolonged storage phases, recycling, mixing, climatic effects and post-depositional perturbation of critical geochemical signals. A move toward first-order quantitative modelling of sedimentary systems and their detrital products can be achieved through development and rigorous testing of integrated, multi-proxy, provenance approaches in parallel with identifying and quantifying the various factors which may modify sand during and after transport. These types of new approaches should ultimately help in achieving the desired output of any provenance study – a predictive tool for both reservoir sandstone distribution and quality.
The “Sediment Tracking” targeted project within the Hydrocarbons spoke of iCRAG aims to address outstanding issues in provenance research by 1) tapping into Irish and international expertise in this area; and 2) utilising sedimentary basins offshore Ireland as a test bed for new techniques. The work builds on recent PIP-funded research developing/applying new provenance proxies, new thermogeochronological approaches, and new geochemical data on regional economic basement, and should ultimately help de-risk exploration in the Irish offshore basins.
For example, there is currently little clarity on the relationship between provenance and reservoir quality, and questions remain as to the extent to which cementation and porosity/permeability evolution can be controlled by the primary detrital mineralogy. These types of questions are being investigated through high resolution sampling and multi-proxy provenance analysis of Triassic sandstones (Sherwood Sandstone Group (SSG) and equivalents) in the Slyne Basin and beyond. These sandstones are the perfect target as their bulk reservoir characteristics are well understood (they host the Corrib Gasfield) yet on smaller scales they comprise heterogeneities (e.g. chloritised zones) which directly impact reservoir quality. These sequences, therefore, allow links between these bed-scale heterogeneities, and changes in sediment supply, to be interrogated.
Other on-going or planned research is targeted at Mesozoic and Cenozoic intervals in the Irish offshore, and includes projects which aim to better understand the connect between onshore structure, uplift history and supply pathways to the offshore basins. In addition, the targeted project aims to constrain sediment transport processes and the potential impact of prolonged hinterland storage. These types of processes could significant modify sediment delivered to the basin and could be especially important in the Irish passive margin basins, particularly during the early Cretaceous and Cenozoic, when, potentially, there is a wide hinterland and shelf area which may have to be traversed prior to ultimate deposition in the Porcupine and Rockall basins.
The aim of this presentation is to provide an overview of work in the “Sediment Tracking” targeted project, focussing on some of the issues related to sediment supply to the Irish offshore basins, highlighting how these issues are being resolved and showcasing some of the new insights being generated through this research. The work also dovetails with other research in the Hydrocarbons spoke and links to elements within the iCRAG platform.