Hydraulic fracture monitoring and optimization in unconventional completions using a high-resolution engineered fibre-optic Distributed Acoustic Sensor

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Understanding fracture geometry and estimating stimulated rock volume (SRV) is the goal of operators in unconventional reservoirs. The industry has long been challenged with getting a good understanding of how wells and completions interact with each other. One of the biggest challenges is how to get a quantitative measure of the extent of fractures. Historically, companies have used many different technologies to better understand their completions. Tilt meters, microseismic geophone arrays, chemical tracers and pressure sensors are just some of the conventional technologies that have been used with a limited coverage to monitor the changes in the reservoir during hydraulic fracturing. The Distributed Acoustic Sensor (DAS) and Distributed Temperature Sensor (DTS) are used for multiple measurements along the entire wellbore. During the hydraulic fracturing treatment, the acoustic energy distribution and temperature profiling are recorded in real time to analyse the fluid allocations per cluster as indicated in Figure 1. The fibre is also used to acquire seismic and microseismic data at different stages of the well completion. Low frequency crosswell strain is also measured in an observation well or in an offset well. DTS data, with a fine resolution of 0.01oC, is used to indicate any hydraulic fluid contact (Hull et al., 2017; Jin and Roy, 2017). The combined microseismic, crosswell strain and temperature data are used to better understand rock properties, well interference and for optimizing the well spacing. The utilization of distributed fibre measurements has been increasing over the past few years. By installing a permanent fibre cable on the outside of a casing string, measurements along the entire wellbore can be achieved (Webster et al., 2013). However, the requirements for the cable orientation and directional perforation adds additional complexity and costs for the installation of the fibre and, therefore, limits the number of wells that can be instrumented with fibre and monitored simultaneously. We present here an advanced Distributed Acoustic Sensor system (referred to here as Carina) that utilizes a new generation of engineered optical fibres (Constellation) with 100x (20 dB) improved sensitivity compared to that of standard fibres.