Reactions and Flow of CO2 Fluid in Compositionally Immature Sandstones Thematic Research
As is commonplace for carbon storage (CS) projects, planned injection sites are necessarily situated tens of kilometres distant from well control, with the target reservoir potentially having experienced a different degree of burial diagenesis and/or provenance than at the well control site (Fig. 1). The projects in this research theme aim to form a generic model that will help reduce the uncertainty and risk that is associated with CS projects that have immature sandstone saline reservoirs. This will be achieved by utilising case studies and geochemical modelling to increase our understanding of how immature sandstone reservoirs respond to injected CO2 fluid, and crucially the magnitude of provenance and diagenetic change necessary to significantly alter that response.
Predicting reservoir response to CO2 that is injected into immature sandstone saline reservoirs is challenging. Unlike compositionally mature sandstones, such as quartz arenite, compositionally immature sandstones, such as arkosic litharenite, contain appreciable feldspars and clays. Not only do certain compositions of these minerals react with and mineralise some of the injected CO2 within the decadal lifetime of a typical CCS project, the products of these reactions may affect the adsorption and dissemination of the fluid within the reservoir and introduce considerable uncertainty to flow models. Critically, the composition and reactivity of the feldspars and clays are highly sensitive to subtle shifts in provenance, depositional environment and burial diagenesis that may either exacerbate or buffer reservoir-CO2 fluid interactions to a significant extent compared with well control models.
Case studies will be used to monitor how intra-basinal provenance and diagenetic variation affect feldspar and clay composition and abundance. A large number of complementary analytical techniques will be employed on samples of immature sandstones as part of these case studies. The breadth of these techniques will enable the effects of provenance and diagenesis to be more confidently delineated. The results of the case studies will be fed into geochemical models in order to evaluate the extent that provenance and diagenetic changes have affected CO2 fluid-reservoir interactions. The first phase of research within this theme comprising the following two projects:
- The impact of provenance and diagenetic reaction gradients on CO2 fluid-reservoir interactions (CASP.RFP.1)
- Fluid flow simulations through different immature sandstone reservoirs (CASP.RFP.2)
The results of the first project will feed into the second. Together, these will improve our understanding of the magnitude of the effect sub-basinal provenance- and diagenesis-driven changes have on CO2 flow. The incorporation of additional case studies from diverse sedimentary facies, it is anticipated that this understanding can be universally applied to the risk assessment for frontier CCS projects using immature sandstone reservoirs.
Contact(s): Michael Flowerdew