Well and Field Monitoring - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 250

If the cement bond between the cement and formation is weak, the fracture may
initiate where there is less resistance and thus not end up being placed in the planned
location, as depicted in Fig. 14.11 . The fluid flow did not go through all perforations
indicating an isolation issue. As both the DTS and MSM show the fracture initiated
and extended in the non-perforated interval, probably due to a poor cement job.
Fig. 14.11 Poor isolation detection using combination of DTS with MSM. Courtesy SPE 136565
Another application of DTS is for checking the plug isolation in a multistage
hydraulic fracturing operation. Figure 14.12 shows a diagnostic response due to
poor stage isolation which is caused by leaking plug or packer, poor cement, or a
leak in the casing. It is hard to discern the exact reason for such occurrences just
using MSM; however DTS can shed more light in such cases as they are near well-
bore issues. By monitoring such problems in real-time, remedial solutions to divert
the fluid to the interval of interest can be assessed and acted on in real time.
Fig. 14.12 Isolation issue revealed by combining MSM and DTS. Courtesy SPE 136565
DAS Applications
In order to discern between backscattered signals, the system must wait for the laser
pulse to travel the full length of the fiber and come back. So the returned frequency
response is a function of pulse frequency and length of fiber. In other words, the
shorter the fiber length, the higher the spatial resolution. Monitoring of strain as
well as temperature allows for additional information to be gathered, for example,
the evaluation of the reliability of swell packer/ball actuated sleeves. Essentially any