For wells where the welbore fluid is brine and the plug flow regime is assumed, the wellbore fluid in a given section should retain its enthalpy for certain duration when it moves along the borehole. If fluid is not lost out of hole, the temperature profile shall move together with the fluid until its feature eventually disappears. In other words, by analyzing movement of the temperature profile, one can derive flow profile in the wellbore.

For old field such as Hacchobaru-Otake in Japan, where the long term production and re-injection may have distorted the hydrological system, cross-flows between the permeable planes occur once the borehole penetrates through them. Water is injected to the well whilst observing transient temperature profiles by Fiber-Optic Distributed Temperature Log which then renders a fluid flow profile for the corresponding hydrostatic column. Once the water injection is stopped, the water level goes back to the original. So does the cross-flow profile. However, since the temperature profile is distorted from the one under the original steady state, the cross-flow profile can be observed by the transient temperature phenomena. Furthermore hydrostatic pressure computed by the water column is valid even for dynamic conditions since the temperature profile is instantly acquired.

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