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Cross-well strain measurements using Low-frequency Distributed Acoustic Sensing (LF-DAS) is an emerging technique to monitor hydraulic fracture propagation. The qualitative interpretations of the strain rate data have been used to evaluate the fracturing stimulation efficiency, hydraulic fracture geometry, and cross-well communication. Limited studies have investigated the cross-well strain signals recorded from offset fibers during zipper fracturing treatment, though zipper fracturing becomes a routine method of stimulating horizontal wells in unconventional reservoirs. This gap will be filled in this research by presenting the methods we developed to investigate complicated LF-DAS signals. These approaches were further demonstrated using field datasets recorded along the two temporal sensing fiber cables during the zipper fracturing operation of seven offset wells with two fracking crews operating simultaneously. By exploring, comparing, and presenting the LF-DAS data recorded in wireline and disposable fiber cables, this research shares the best practices for visualizing and interpreting cross-well strain signals. The LF-DAS dataset shown in this study, which, to the best of our knowledge, is one of the most complicated LF-DAS datasets presented. The approaches proposed here can be extended and applied to visualize and interpret different kinds of complicated LF-DAS signals recorded using permanent, wireline, and disposable fiber cables.
Cross-well strain measurements using Low-frequency Distributed Acoustic Sensing (LF-DAS) is an emerging technique to monitor hydraulic fracture propagation. The qualitative interpretations of the strain rate data have been used to evaluate the fracturing stimulation efficiency, hydraulic fracture geometry, and cross-well communication. Limited studies have investigated the cross-well strain signals recorded from offset fibers during zipper fracturing treatment, though zipper fracturing becomes a routine method of stimulating horizontal wells in unconventional reservoirs. This gap will be filled in this research by presenting the methods we developed to investigate complicated LF-DAS signals. These approaches were further demonstrated using field datasets recorded along the two temporal sensing fiber cables during the zipper fracturing operation of seven offset wells with two fracking crews operating simultaneously. By exploring, comparing, and presenting the LF-DAS data recorded in wireline and disposable fiber cables, this research shares the best practices for visualizing and interpreting cross-well strain signals. The LF-DAS dataset shown in this study, which, to the best of our knowledge, is one of the most complicated LF-DAS datasets presented. The approaches proposed here can be extended and applied to visualize and interpret different kinds of complicated LF-DAS signals recorded using permanent, wireline, and disposable fiber cables.
The downhole monitoring of strain using Fiber Optics (FO) can reveal unique information about the propagation and geometry of hydraulic fractures between nearby wells during stimulation and production. This work aims at creating a catalogue of commonly observed strain-rate signals captured in a not yet stimulated nearby observation well equipped with either a permanently or temporarily installed FO cable. This catalogue is the result of an informal collaboration between experience FO users from academia, service providers, consulting companies, and operators. In the creation of this first edition of a strain-rate catalogue, we considered two main types of stimulation categories (single and multi-entry) as well as the angle between the hydraulic fractures and the segment of the well where the strain-rate signals are observed (horizontal vs. vertical segments). In the catalogue we show a series of representative examples of two main types of far-field strain Fracture Driven Interactions (s-FDI) commonly encountered in frac diagnostics: 1. Vertical hydraulic fractures being monitored in a lateral portion of a horizontal well and 2. Vertical fractures being monitored in a vertical observation well. The catalogue is organized around commonly observed s-FDI motifs. Because interpretation of observed strain-rate signals can be subjective, when possible, we included observed examples with a brief description of our interpretation, as well as synthetic signals from geomechanical models of similar motifs. The strain-rate motifs were modeled based on first physical principles for rock deformation. These models serve to support the proposed interpretation of the observed signals. FO strain rate monitoring is changing our understanding about the hydraulics fracturing process. The information from FO strain is not available by other commonly used fracture diagnostic techniques. Strain- rate fractures driven interactions between wells occur in predictable patterns (Frac Domain and Stage Domain Corridors – FDC & SDC respectively) which are typically in line with the cluster spacing and stage length in the borehole being stimulated. Using FO strain monitoring, we now know that hydraulic fractures are larger than first anticipated, both in length and height. Many examples indicated that there is a direct correspondence between the near-field and far-field stimulation geometries. The lack of isolation due to cement quality and or plug failure manifests in the far-field geometries observed via FO strain-rate in nearby wells. The use of FO strain monitoring has also revealed that reopening of hydraulic fractures is common not only between prior and infill wells but also between wells from the same stimulation vintage. All these observations and conditions must be considered when interpreting new strain-rate datasets and more importantly when designing new hydraulic fracturing operations and considering different stimulation order (zipper schedule), as well as when making decisions about the vertical and lateral spacing of adjacent wells. The purpose of this industry-first edition strain-rate catalogue is to aid, new and experienced FO users, on the interpretation of strain-rate datasets. Ultimately, the accurate interpretation of FO strain data will not only help calibrate geomechanical and reservoir models but also directly influence where and how we complete unconventional wells. Nowadays, many s-FDI examples exist in scattered publications with formats that aren’t easily comparable for new users of the technology. In this project, we expand upon those publications to create an encompassing analysis with up-to-date interpretations where we have formalized the formatting of figures for better readability (color scheme, scales, etc.). What has resulted from this collaborative effort is a novel catalogue not available before in the FO published literature.
The large quantity of batch wells typical in unconventional fields results in per well incremental optimisation gains compounding and significantly improving asset economics. A disposable, cost effective, fibre optic intervention system safely and efficiently provides high quality data to optimise completion design and hydraulic fracturing, calibrate reservoir models and inform future well design. CO₂ efficiency estimates and technology applications in unconventional fields including Vertical Seismic Profiling (VSP), cement cure analysis and hydraulic fracture optimisation are outlined. The upper end of one or two bare fibre optic cables are fixed inside a light-weight pressure control cap, while the downhole ends are deployed along the wellbore as they unspool from a disposable probe which is pumped along horizontal sections. Distributed Acoustic Sensing (DAS) is used for seismic and micro-seismic fracture analysis, whereas Distributed Temperature Sensing (DTS) is used to monitor well and near wellbore fluids. The high-quality data is used both in real time and subsequent enhanced analysis with disposable fibre having been successfully deployed in over 200 unconventional wells. The high level of acoustic and strain coupling as well as the elevated sensitivity of disposable bare optic fibre produce high quality data, with recent studies favourably comparing disposable fibre data with that obtained by retrievable fibre optic intervention. When compared with well monitoring methods utilising Wireline or Coiled Tubing, the disposable fibre system is extremely light weight with a micro footprint, requires only one person to deploy, has static seals, and does not require a BOP. The result is a low risk, efficient, method of highly sensitive, complete wellbore, fibre optic sensing. The transportation weight saving, reduced survey time, power consumption and reduced personnel requirements result in significant operational CO₂ reductions. Examples of unconventional well VSP, cement cure analysis, well integrity and fracture optimisation applications demonstrate efficiency gains and impact on asset economics. Unconventional field lifecycle applications of a new disposable fibre optic system are presented along with field optimisation and economic benefits. In addition, an example operation illustrating comparative CO₂ emissions for a hydraulic fracture monitoring application demonstrates disposable fibre CO₂ emissions at 8% of comparable wireline operations.
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