def td_from_t(t_hr, k_mD=10, phi=0.2, mu_cP=1, ct_1atm=1e-5, rw_m=0.1):
    """
    dimension time conversion to dimensionless time
    t_hr - dimensional time, hour
    k_mD - formation permeability, mD
    phi - porosity, fractions of units
    mu_cP - dynamic fluid viscosity, cP
    ct_1atm - total compressibility, 1/atm
    rw_m - well radius, m
    """
    return 0.00036 * t_hr * k_mD / (phi * mu_cP * ct_1atm * rw_m * rw_m)