Case study of hydraulic fracture monitoring using multiwell integrated analysis based on low-frequency DAS data

Abstract

Distributed acoustic sensing (DAS) is an effective technique for hydraulic fracture monitoring. It can potentially constrain fracture propagation direction and time while monitoring strain perturbation, such as stress shadowing. In this study, we acquired passive DAS and distributed temperature sensing (DTS) data throughout the entire fracturing operations of adjacent production wells with varying offset lengths from the fiber-optic cable in the Montney tight gas area. We applied data processing techniques to the DAS data to extract low-frequency components (less than 0.5 Hz) and to construct the strain rate and cumulative strain maps for detecting responses related to fracture hits along the fiber-optic cable. We used low-frequency DAS (LF-DAS) results to estimate the fracture hit position and time, and in certain cases, to additionally estimate the fracture connection. By integrating LF-DAS results with DTS results, we detected the temperature changes around the compression response near the fracture hit position and time. Furthermore, we observed that timing of the fracture hit can be constrained more precisely by using high-frequency DAS data (greater than 10 Hz). We estimated the fracture propagation direction and speed from the estimated fracture hit position and time. The fracture propagation direction deviated slightly from a perpendicular line to the fiber direction. In addition, as estimated from the first fracture hit time, the fracture length and fluid injection volume had a proportional relationship. Due to challenges associated with the data, it is important to design data acquisition geometry and fracturing operations on the premise of acquiring LF-DAS data. It is also important to apply an additional noise reduction process to the data.

A Review of Distributed Fiber–Optic Sensing in the Oil and Gas Industry

“…Besides the aforementioned advantages of optical fibers, distributed fiber-optic sensors have another major benefit of reducing the overall sensing cost by measuring sensing parameters continuously and in real-time over tens of kilometers. In the upstream sector, distributed fiber-optic sensors are used for a wide range of applications such as seismic profiling [27], hydraulic fracture analysis [28], flow monitoring [23], casing leak detection [29], gas lift optimization [24], diagnosis [23], among others (Fig. 2(a)).…”

“…As a representative example, we present a recording of a hydraulic fracturing process using a low-frequency (0-0.5 Hz) DAS (LF-DAS) [28]. In an observation well, an optical fiber cable is installed behind the casing.…”

“…To clarify, It is important to highlight that the low-frequency (< 2 Hz) DAS is cross-sensitive to strain and temperature perturbations [60]. Hence in [28], another optical fiber cable was installed for DTS measurement to further understand the temperature changes around the compression response near the fracture hit position and time.…”

Seismic Applications of Downhole DAS

“…The different interpretation components have been validated by fracture modeling [116,117] and analysis at different sites [41,107,118]. A recent study [119] applied a similar analysis to a multiwell DAS acquisition and could track fracture trajectories and propagation velocity by their intersection with the DAS-equipped wells. Conventional downhole tools are not sensitive in this frequency range.…”

Fracture Imaging Using DAS-Recorded Microseismic Events

“…Another type of fiber-optic-based measurement during hydraulic fracturing used to describe fractures is of low-frequency ( < 1 Hz) DAS (LFDAS). LFDAS measures strain changes (i.e., works as hybrid distributed strain sensing, DSS) induced by hydraulic fractures (Jin and Roy, 2017;Richter et al, 2019;Ugueto et al, 2019;Ichikawa et al, 2020;Zhu and Jin, 2021). The detected strain signals represent fractures which were initiated at the offset treatment well and reached the monitoring fiber well, so-called fracture hits or frac-hits.…”