Quantifying Fluid Flow in Stressed & Fractured Carbonates
Lead Research Organisation:
University of Aberdeen
Department Name: Sch of Geosciences
Abstract
We urgently need to develop new renewable energy sources in the UK, and this will take international collaboration with those countries further along the development path. Our project will build a quantitative model that links the fluid flow through fractured limestone with the local state of in situ stress, using existing data and expertise from Italy and Germany. Geothermal energy is potentially important for the UK because the Lower Carboniferous Limestone (LCL) formation underlies large urban areas, e.g., Manchester, Liverpool and Bristol, and is a viable source of geothermal energy, especially for supplying heat.
In the LCL, it is believed that fluid flows mainly through fractures rather than through the rock grains in between the fractures. This means that we need to better understand how fluid flows in fractured limestones under natural stresses occurring at depth. Several different models and methods have been proposed to explain this linkage but we cannot test these models in the UK yet, because we lack the relevant data on the fracture networks, the fluid flow rates and the in situ stress at depths of two or more kilometres.
This proposed new collaboration with our Italian partner will use large datasets from previous studies on limestones in southern Italy - the Upper Agri valley near Potenza. The datasets available cover fractures, fluid flow rates from water and oil boreholes, and in situ stresses. We will collate all these data and, with help from new project partners in Germany, build a digital 3D model of the fractured subsurface beneath the Agri valley, spanning 30 x 10 x 5 km (length x width x depth). In this model, we will impose stresses on the fractures (based on the stress data from Italy) and predict the fluid flow from simulated boreholes. By comparing these model predictions of fluid flow to the measured borehole flow rates from boreholes Italy we can test the competing hypotheses for the dominant controls on fluid flow in stressed limestone fractures. This then provides a scientifically robust foundation on which to build future analyses of potential fluid flow in the fractured and stressed limestones beneath the UK. In the future, we will be able to adapt our tested model for the Agri valley to the specifics of the UK Lower Carboniferous Limestone, to help companies and other agencies to develop their plans to drill safe and cost-effective boreholes for geothermal energy.
In the LCL, it is believed that fluid flows mainly through fractures rather than through the rock grains in between the fractures. This means that we need to better understand how fluid flows in fractured limestones under natural stresses occurring at depth. Several different models and methods have been proposed to explain this linkage but we cannot test these models in the UK yet, because we lack the relevant data on the fracture networks, the fluid flow rates and the in situ stress at depths of two or more kilometres.
This proposed new collaboration with our Italian partner will use large datasets from previous studies on limestones in southern Italy - the Upper Agri valley near Potenza. The datasets available cover fractures, fluid flow rates from water and oil boreholes, and in situ stresses. We will collate all these data and, with help from new project partners in Germany, build a digital 3D model of the fractured subsurface beneath the Agri valley, spanning 30 x 10 x 5 km (length x width x depth). In this model, we will impose stresses on the fractures (based on the stress data from Italy) and predict the fluid flow from simulated boreholes. By comparing these model predictions of fluid flow to the measured borehole flow rates from boreholes Italy we can test the competing hypotheses for the dominant controls on fluid flow in stressed limestone fractures. This then provides a scientifically robust foundation on which to build future analyses of potential fluid flow in the fractured and stressed limestones beneath the UK. In the future, we will be able to adapt our tested model for the Agri valley to the specifics of the UK Lower Carboniferous Limestone, to help companies and other agencies to develop their plans to drill safe and cost-effective boreholes for geothermal energy.
