The Impact of Fault-Fracture Interaction on Fluid Flow in Carbonates: Laboratory Experiments

Understanding the impact of faults and natural fractures on fluid flow in petroleum reservoirs is important at all stages of a field's development. Sealing faults compartmentalise reservoirs, reducing the rate of oil production by locally reducing permeability; the presence of sealing faults usually requires more wells or more complex wells to be drilled to achieve production targets (Smith, 1966; Berg, 1975; Watts, 1987; Alexander and Handschy, 1998; Fisher et al., 1998: Fisher et al., 2001; Fisher et al., 2005; Fisher et al., 2013). Open fractures and/or dilatant faults may enhance productivity (Coney et al., 1993) but may also cause production problems, such as early water breakthrough in producer wells (Rawnsley and Wei, 2001). Single extensional fractures may develop vuggy porosity or become partially sealed, i.e. their permeability may become modified by dissolution or karstification (Nelson 2001). Some reservoirs can contain both open fractures and low-permeability fault rocks (Nelson, 2001; Geraud et al., 2006; Micarelli et al., 2006; Ran et al., 2014, Al Hashemi et al., 2023; Al Hashemi et al., 2024). There exists a lack of understanding of how open fractures and low-permeability faults interact and affect fluid flow. To fill this knowledge gap, a series of fluid flow experiments were conducted on carbonates with open fractures and low- permeability barriers (i.e. analogous to low-permeability faults). The main objective of the experimental study described in this paper is to assess the impact that low-permeability faults in conjunction with open fractures have on oil production. In particular, the experiments compare the production behaviours of samples with sealing faults to those in which open fractures breach the sealing faults; the latter are referred to as partially sealing faults. It is critical to emphasise that the flow behaviour achieved by core flooding in the laboratory is on a much smaller scale than that of a reservoir, so up-scaling is an issue.