Modelling of hydraulic leakage by pressure and stress simulations and implications for Biot's constant; an example from the Halten Terrace, offshore mid-Norway

A coupled pressure and stress simulator has been applied to the reservoir sandstone unit, the Middle Jurassic Garn Formation in the Halten Terrace, offshore Mid-Norway, in order to simulate hydraulic fracturing and leakage due to overpressure. The over- and underlying rocks are used as vertical seals to the compartments. The overpressure generation within the pressure compartments was modelled quantifying the mechanical and chemical compaction. An empirical model for the minimum horizontal stress was applied to the Griffith-Coulomb failure criterion to estimate the pressure levels at which hydraulic fracturing occurs. Sensitivity tests of Poisson's ratio and Young's modulus, which control Biot's constant, show an effect on the accumulations of overpressure during time. Defining Biot's constant equal to 1 results in too early pressure build up and hydraulic leakage in the western parts of the basin. Lower values of Biot's constant (>0.85) give a present-day pressure distribution closer to the measured pressures in wells. The Kristin compartment is simulated to experience hydraulic failure around 1.5 Ma. High values of the coefficient of internal friction (mu ) and the coefficient of sliding friction (mu '), which are used in the failure criteria, results in a time-delay in failure and, thereby, less leakage from overpressured compartments.