| Abstract |
One of the novel applications for the fiber optic sensor is to acquire instantaneous distributed temperature along the cable. The measurement mechanism is based on Raman back scattering whose intensity is sensitive to temperature. The advantage of instantaneous acquisition of distributed temperature over the entire borehole is manifold. The obvious one is to be able to measure transient temperature phenomena better. For example, temperature recovery test has been routinely conducted by a few temperature logging runs whilst each run separated by certain time intervals. Regardless of the model used to derive geostatic temperature, only a few points on the plot are available. With temperature profile over the entire borehole with sampling rate of 1 minute or so, the fiber optic temperature logging enables us to optimize the time required to determine whether the plot fits to the model. The unique feature of the fiber optic distributed temperature sensor can be used as fluid flow logging which is to obtain velocity profile whilst injecting water into fractured type highly productive well. As water is injected into borehole, the fluid column is pushed downwards. Since the flow in such a condition behaves mostly as plug flow, temperature profile should move at the same velocity as the fluid flow. In other words the change of temperature profile should yield the fluid flow profile. The fluid flow seen by the temperature profile change is best detected by the movement of a fluid boundary showing high temperature contrast such as the one between cool injected water and hot geothermal water or other area where sharp temperature contrast is present regardless its cause. The velocity profile is used to analyze fluid entry and their flowrates. The velocity detection is so sensitive that it may be possible to derive borehole diameter if the fluid velocity profile deeper in the hole shows no fluid loss into formation above. If it is conducted at the end of temperature recovery test, it could yield information otherwise requiring temperature log, flowmeter log and caliper log. |