A method comprising: changing a wellhead pressure to induce a distributed temperature change along a portion of a wellbore ; measuring a time varying temperature along the portion of the wellbore due to the inducing; and determining a distributed flow rate in the portion based on the measured time varying temperature before the temperature reaches equilibrium, wherein: changing the wellhead pressure comprises using a surface-disposed wellhead valve ; and the act of determining the distributed flow rate further comprises: modeling the time varying temperature as an exponential function characterized by a time constant; determining the time constant of the temperature, the time constant being indicative of a heat transfer coefficient of the portion of the wellbore; determining the heat transfer coefficient based on the determined time constant; determining a Nusselt number for a ratio of convective to conductive heat loss based on the determined heat transfer coefficient; determining a Reynold's number based on the Nusselt number; and determining a mass flow rate based on the Reynold's number. changing a wellhead pressure to induce a distributed temperature change along a portion of a wellbore ; measuring a time varying temperature along the portion of the wellbore due to the inducing; and determining a distributed flow rate in the portion based on the measured time varying temperature before the temperature reaches equilibrium, wherein: changing the wellhead pressure comprises using a surface-disposed wellhead valve ; and the act of determining the distributed flow rate further comprises: modeling the time varying temperature as an exponential function characterized by a time constant; determining the time constant of the temperature, the time constant being indicative of a heat transfer coefficient of the portion of the wellbore; determining the heat transfer coefficient based on the determined time constant; determining a Nusselt number for a ratio of convective to conductive heat loss based on the determined heat transfer coefficient; determining a Reynold's number based on the Nusselt number; and determining a mass flow rate based on the Reynold's number. changing the wellhead pressure comprises using a surface-disposed wellhead valve ; and the act of determining the distributed flow rate further comprises: modeling the time varying temperature as an exponential function characterized by a time constant; determining the time constant of the temperature, the time constant being indicative of a heat transfer coefficient of the portion of the wellbore; determining the heat transfer coefficient based on the determined time constant; determining a Nusselt number for a ratio of convective to conductive heat loss based on the determined heat transfer coefficient; determining a Reynold's number based on the Nusselt number; and determining a mass flow rate based on the Reynold's number. modeling the time varying temperature as an exponential function characterized by a time constant; determining the time constant of the temperature, the time constant being indicative of a heat transfer coefficient of the portion of the wellbore; determining the heat transfer coefficient based on the determined time constant; determining a Nusselt number for a ratio of convective to conductive heat loss based on the determined heat transfer coefficient; determining a Reynold's number based on the Nusselt number; and determining a mass flow rate based on the Reynold's number. <EOS>