Fiber optic distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) have been used to monitor and diagnose the integrity of wellbores (leak detection, gravel-pack screen damage, formation subsidence, etc.), the performance of reservoirs and wells (production profile, injection profile, etc.), used for surveillance and other applications for quite some time. The application of high resolution fiber optic DAS and DTS during multi-stage hydraulic fracturing has increased in recent years.
In this horizontal tight-gas well, the fiber optic filaments were placed in a small stainless steel tube which was clamped to the casing while running in hole, and the casing was then cemented in place. Perforations had to be oriented to avoid damage to the fiber optic. In this case, perforations were place at the topside of the casing, zero degree phasing, at 5 shots per foot (1 foot per cluster).
This paper shares results from DAS and DTS techniques that allow for interpretation of fracturing treatments in multi-cluster (each stage), multi-stage horizontal well with cemented casing and ‘plug and perf’ completion process. The images illustrate the dynamics pertaining to initiation, propagation and arrest of hydraulic fractures during simultaneous stimulation of multiple clusters. First, fracture initiation appears not only during early time, as expected, but late time initiation events may develop in seemingly dormant clusters. Second, propagation of multiple fractures can occur randomly within a cluster array. Third, dominate clusters are often observed during stimulation. Further, during the treatment cycle, the position of dominate cluster(s), within a given stage, may actually change.