Fiber Optic Distributed Acoustic Sensing of Multiple Fractures in a Horizontal Well

Abstract

This paper highlights the current state of fiber optic distributed acoustic sensing (DAS) technology by reviewing its application to hydraulic fracture diagnostics in a multi fractured horizontal well (MFHW). It will be shown that, with the advent of DAS, a gap in the feedback — which could previously occur using various hydraulic fracture diagnostic options — has been filled. Results are shared that were obtained from the first successful application of high resolution DAS during the placement of multiple hydraulic fractures in a horizontal well that was completed with an open hole packer and frac valve system. Observations of the real time acoustic soundfield in the near wellbore (NWB) region during hydraulic fracturing are presented as high resolution images. These images have enabled an analysis of key dynamic aspects of the fracturing process. In examining the resultant data, it has become apparent that DAS has overcome some limitations intrinsic in other diagnostic tools such as distributed temperature sensing (DTS), microseismic monitoring, and tracer programs. An overview of the well design is provided as well as selected samples from the dataset which highlight some of the events that were observed during the hydraulic fracturing process. Sample images are used to demonstrate the current capability of DAS measurement, selected both from the real time soundfield display (SFD) and from processed high resolution soundfield maps. DAS processing methods are briefly discussed, as well as two categories of field observations— which highlight some of the mechanical reliability aspects of the swell packer/ball actuated frac sleeve system, as well as some aspects of the near wellbore region during hydraulic fracturing such as single or multiple fracture initiation sites and the general behaviour of wellbore fluids over the course of the fracture treatment. Distributed acoustic sensing using a single mode optic fiber has been described in recent literature (Molenaar, 2011) for applications involving the recording of acoustic events during various stages of well completion and stimulation. The current paper provides further description on how DAS works and shares results from a high resolution DAS survey, obtained while placing multiple hydraulic fractures in a horizontal well, completed in a tight sand using an openhole ball actuated valve system with swell packers for fracture isolation. Earlier findings are supported, in particular that DAS will enable an improved understanding of in-wellbore activities and, in so doing, that it will enable optimization of hydraulic fracturing design and execution. It is recognized that much is yet to be learned in the processing of fiber optic DAS data, but also that it would be beneficial to share the work that has been completed to date to facilitate accelerated development of DAS processing technology.

Advancement of Hydraulic Fracture Diagnostics in Unconventional Formations

“…Furthermore, the thermal conductivity of the tubular and the fiber does not affect DAS measurements. [62] discussed the application of real-time DAS measurement for fracturing a horizontal well in tight sand. In gas-producing wells, successful production profiling using DAS has been reported by [30] presented DAS strain front analysis from hundreds 4 Geofluids of stages across a range of completion systems, with the results allowing for improved well azimuth techniques and stage offsetting.…”

Hydraulic fracture diagnostics from Krauklis-wave resonance and tube-wave reflections

“…The model presented in this study would need to be extended to predict the signals in the monitoring wells, and it is uncertain if these signals would have as much useful information regarding the fracture geometry. Another technology that reduces the influence of the tool on tube-wave propagation is fiberoptic distributed acoustic sensing (DAS) (MacPhail et al, 2012;Molenaar et al, 2012;Boone et al, 2015). DAS cables can run through grooves across swellable packers along the casing in the sealing elements in uncemented packer and sleeve completion, and they can be buried in the cement in cemented plug-and-perf completions (Boone et al, 2015).…”

Brief history of fiber optic sensing in the oil field industry

“…In recent years, the use of distributed acoustic sensing (DAS) has been explored for potentially providing in-well seismic profiling 22 , flow measurement 23 , and fracture effectiveness 24 . The first installations of optical fiber specifically for DAS measurements were in 2009; since that time, there have been multiple installations.…”