
 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.

A Catalogue of Fiber Optics Strain-Rate Fracture Driven Interactions

A compact design of defected ground antenna working in L-band is proposed in this communication. The antenna resonates in the frequency range between 1–2 GHz. The parameters such as return loss, input impedance, antenna gain and side lobe level are thus presented and discussed. A comparison is also shown for the proposed antenna with the antenna structure without defect. A very good return loss of −32 dB with a gain of 6.6 dBi is obtained for the defected ground structure (DGS) ring antenna.

Improved characteristics of DGS ring antenna in L-band

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.

Challenges and Best Practices in Interpreting Cross-well Strain Signals to Monitor Multi-Crew Zipper Fracturing Operations


 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.

Disposable Fibre Optic Surveys Optimise Wells and Reduce CO2 Emissions in Unconventional Assets

Summary Distributed fiber-optic (FO) strain measurements have become a widely used method for monitoring and diagnosing far-field strain induced during hydraulic fracturing (HF). However, field observations have revealed that the mechanical decoupling between the fiber and the rock often happens. Despite this phenomenon, much of the current research assumes that the fiber cable remains mechanically coupled to the rock formation. To improve the accuracy and reliability of field data interpretation, it is essential to better understand the effect of fiber decoupling on strain responses. The objective of this study is to simulate strain responses while taking into account the impact of fiber slippage. In this study, we developed a numerical model that allows for accurate prediction and analysis of strain responses of crosswell distributed FO experiencing mechanical decoupling. Our model first uses the 3D displacement discontinuity method to calculate displacement fields induced by hydraulic fractures. The model then accounts for the occurrence of slippage and calculates the fiber displacement distribution with slippage effect. Additionally, the model can predict fiber strain distribution in cases where the stick-slip behavior is present. To better understand the impact of friction on strain and strain-rate signals, we conduct a sensitivity analysis. This allows us to explore the effects of different friction levels on the signals, which can be critical in achieving more accurate and reliable results. Our model results reveal several key observations. First, when fiber slippage is detected, we typically observe a broadening of the extension zone near the fracture on the strain/strain rate waterfall plots, which cannot provide a well-defined fracture domain corridor. The simulated strain rate pattern matches the field observation. Additionally, the size of the decoupling zone increases as the friction between the fiber and formation decreases. Also, the decoupling generates negative cumulative strain change after a certain period of closure. Furthermore, when the dynamic friction is smaller than the static friction, sudden strain releases appearing as sticking portions were visible in the strain/strain-rate waterfall plots, indicating the occurrence of stick-slip behavior in the fiber. We also observed that the sudden strain releases in the strain rate waterfall plot occur more frequently when the maximum fiber strain gradient is smaller. Moreover, the longer sticking portion was observed when the dynamic/static friction ratio was smaller. The key innovation of this study is the development of a forward numerical model that simulates strain responses while taking into account the coupling effect between fiber and formation. To the best of our knowledge, this is the first time that such a model has been presented. Overall, our study provides an important contribution to the field of HF monitoring by enabling a more accurate and reliable interpretation of strain signals, which can ultimately improve the safety and effectiveness of HF operations. 

A Numerical Model for Analyzing Mechanical Slippage Effect on Crosswell Distributed Fiber-Optic Strain Measurements During Fracturing


 The use of fiber-optic-sensing technology for the evaluation of completion efficiency, primary cement sheath integrity, and offset well interference has become more prevalent in recent years. In addition, the use of a fiber-optic cable for microseismic monitoring as opposed to traditional wireline-conveyed geophones was recently introduced. Various fiber deployment methods have been developed over the years to allow operators to make rapid decisions in real-time based on distributed acoustic sensing (DAS), distributed temperature sensing (DTS), and microseismic data, all provided by a small fiber- optic cable deployed in the well and monitored at surface via sophisticated interrogation equipment.
 Historically, fiber-optic cables were deployed in a permanent configuration, strapped to the production casing, in a manner similar to a standard control line, and deployed with the casing prior to cementing. Permanent fiber has become simpler and cost effective over time and provides valuable near wellbore information - and there are continuous developments to keep reducing that cost and complexity. Some operator focus has been less on the monitoring of the completion efficiency metrics and more on understanding the cross well interference data provided from fiber. As a result, operators have looked to other, temporary-type deployment options for fiber.
 Two typical temporary deployments are via coiled-tubing and an armored fiber-optic cable. For the first method, a fiber-optic cable is fed into a coiled-tubing reel and then deployed downhole to monitor the strain when the well is impacted or closely impacted by a hydraulic fracture from an adjacent well. An armored fiber-optic cable deployment is similar to electric wireline in that it is installed in the well during pump down or with a wireline tractor.
 Both these options are viable and readily available; however, they include supplementary expenses in terms of equipment required to convey the fiber into the well. In addition, the surface footprint required during the conveyance and monitoring phases of the operation is substantial with crane(s), a coiled-tubing unit or wireline unit, and associated on-location equipment required during the job. Figure 1 depicts a wireline-conveyed fiber operation in conjunction with fracturing operations. Additional equipment in the form of a wireline truck and extra crane are highlighted in yellow. In contrast, a wellsite where disposable fiber is being deployed is shown in Figure 2. Once the fiber is landed, the pump units are removed and only a trailer and crew pickup remain on-site.
 Figure 1 Typical fracturing operation, wireline-conveyed fiber
 Figure 2 Typical offset well monitoring wellsite, disposable fiber
 This paper will discuss a new, low-cost option now available to conduct cross well monitoring and microseismic evaluation of offset completions using a disposable optical fiber that requires minimal equipment to deploy into the wellbore, reduces surface impact during the operational phase, provides quality strain information with excellent quality microseismic data when compared to other fiber-optic deployment methods, and is able to be disposed of at the conclusion of the operation with no detriments or impediments to the completion of the well it has been deployed in. This fiber was successfully deployed for the first time in the Marcellus Shale for Chesapeake Energy with minimal operational disturbance and reduced costs when compared to similar technologies. It was demonstrated to provide valuable data for the purposes of understanding the impact of hydraulic fracturing on far-field communication and evaluating both the temporal fracture response and zonal impact caused by structural changes across the lateral.

Application of Disposable Fiber Technology to Evaluate Far-Field Communication and Fracture Performance in the Marcellus Shale

The ORS Payload Development Initiative awarded 14 contracts to develop basic to complex technologies for potential TacSat missions. The largest of the complex awards, announced in February 2007, went to Ball Aerospace and its partner ATK to perform development and risk reduction for a light-weight L-Band Synthetic Aperture Radar antenna. The program, started in April, 2007, has focused on determining the most practical and highest-performing configuration for the antenna and in reducing risk and increasing feasibility of the overall design. The motivation for this L-band SAR system, which can provide worldwide coverage daily with only two satellites, is to enable uniquely perceptive monitoring of near-real-time changes over broad regions of interest. Where further investigation is required, this would be provided by tasking more focused sensors. In developing the L-Band SAR antenna, Ball Aerospace has focused on the distributed architecture design of the radiating aperture and ATK has focused on the lightweight backing structure and deployment systems. The optimized design consists of modular tiles of 2x2 radiating elements with transmit and receive functionality provided by local electronics. 416 of these “quad” module assemblies (QMA) are mounted on stable lightweight composite panels to form a contiguous 28 m 2 aperture, with linking deployment mechanization that is derivative of heritage solar array designs. The program is preparing a complete design review documentation package and building proof of concept models that will be used to validate the capabilities of the antenna in the relevant environment. The paper will review the system design and present preliminary results from the engineering model tests.

Technology Development for Lightweight L-Band SAR

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Application of Disposable Fiber Technology to Evaluate Far-Field Communication and Fracture Performance in the Marcellus Shale

Technology Development for Lightweight L-Band SAR