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Abstract 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), the performance of reservoirs and wells (production profile, injection profile), used for surveillance and communication networks for quite some time. Though still somewhat novel, the application of high-resolution fiber optic DAS and DTS during multistage hydraulic fracturing has increased in recent years. This paper shares DAS and DTS images of fracture initiation, fracture propagation and fracture progression during fracturing treatments of multicluster (each stage), multistage horizontal tight-gas well. 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. Introduction Placing the fractures where intended along the horizontal wellbores effectively and efficiently in each frac stage is a challenge when developing low-permeability and/or unconventional reservoirs. The plug-and-perf completion process is thought to enable and dictate multiple and simultaneous fracture initiation and propagation. However, accurate and reliable measurements and detection of fracture placement are difficult to accomplish. Some diagnostic tools to detect and identify the locations of the fractures include radioactive and chemical tracer surveys, microseismic monitoring, fiber optic distributed temperature sensing (DTS), and fiber optic distributed acoustic sensing (DAS). Each technology has advantages and disadvantages. Many of these applications can be used for monitoring, interpretation and diagnostic in real-time (or quasi-real-time) during the fracturing process with various degrees of accuracy. Several of these technologies can also be leveraged for monitoring and diagnostics during flow-back/production. Comparison and correlation of the interpretation and diagnostics between these applications should give better insights of fracture initiation, propagation, and progression with time. |
