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.

Distributed Fiber Optics Sensing (DFOS) is a mature technology, with known, tested, verified, and even certified performance of various interrogators and measurement methods, which include Distributed Temperature Sensing (DTS), Distributed Temperature-Strain Sensing (DTSS), and Distributed Acoustic Sensing (DAS). This paper reviews recent progress in two critical areas of DFOS implementation in large scale civil engineering structures. First is the substantial improvement in sensing accuracy achieved by replacing Brillouin scattering-based measurements with its Rayleigh counterpart. The second is progress in acquisition speed and robustness, as now engineers can observe parameters of interest in real-time, and make informed, operational decisions regarding quality and safety. This received a high valuation from field engineers when used during the construction stage of the project. Furthermore, this change in the use of DFOS in civil engineering greatly increases the practical possibility of installing FO cables permanently. The same FO cables can be later used for long-term monitoring, during maintenance periods throughout the structure’s lifetime. To illustrate these two advances, we present a comparison between Brillouin and Rayleigh scattering measurements, and their accuracy, and highlight the importance of temperature and strain separation. We also present several important applications in large scale civil engineering infrastructure projects.

Distributed acoustic sensing (DAS) in optical fibers detect dynamic strains or sound waves by measuring the phase or amplitude changes of the scattered light. This contrasts with other distributed (and more conventional) methods, such as distributed temperature (DTS) or strain (DSS), which measure quasi-static physical quantities, such as intensity spectrum of the scattered light. DAS is attracting considerable attention as it complements the conventional distributed measurements. To implement DAS in commercial applications, it is necessary to ensure a sufficiently high signal-noise ratio (SNR) for scattered light detection, suppress its deterioration along the sensing fiber, achieve lower noise floor for weak signals and, moreover, perform high-speed processing within milliseconds (or sometimes even less). In this paper, we present a new, real-time DAS, realized by using the time gated digital-optical frequency domain reflectometry (TGD-OFDR) method, in which the chirp pulse is divided into overlapping bands and assembled after digital decoding. The developed prototype NBX-S4000 generates a chirp signal with a pulse duration of 2 μs and uses a frequency sweep of 100 MHz at a repeating frequency of up to 5 kHz. It allows one to detect sound waves at an 80 km fiber distance range with spatial resolution better than a theoretically calculated value of 2.8 m in real time. The developed prototype was tested in the field in various applications, from earthquake detection and submarine cable sensing to oil and gas industry applications. All obtained results confirmed effectiveness of the method and performance, surpassing, in conventional SM fiber, other commercially available interrogators.

Attempts in digital management of structures are among the most popular topics in the trend of Information of Things (IoT). However, the implementation lags behind. This work recognized that Computer Aided Design (CAD) comprises the core of modern engineering; thus, most digital information can be available if CAD is used not only in design but also for life cycle structural health monitoring (SHM). Based on this concept, the newly designed method utilizes the isogeometric analysis (IGA) tool to include the Distributed Fiber Optic Sensing (DFOS) information by proposing a fiber mesh model. The IGA model can be obtained directly from CAD, and the boundary conditions can be provided directly or indirectly from DFOS in real time and remotely. Hence a practical method of SHM is able to achieve highly efficient and accurate numerical model creation, which can even accommodate non-linear constitutive property of materials. The proposed method was applied to a pipe deformation model as an example. The inverse analysis method is also shown to determine the contact force for loading on the pipe, which shows the potential for many engineering applications.

The characteristics of hydraulic fractures in the near-wellbore region contain critical information related to the production performance of unconventional wells. We demonstrate a novel application of a fiber-optic-based distributed strain sensing (DSS) technology to measure and characterize near-wellbore fractures and perforation cluster efficiency during production. Distributed fiber-optic-based strain measurements are made based on the frequency shift of the Rayleigh scatter spectrum, which is linearly dependent on strain and temperature changes of the sensing fiber. Strain changes along the wellbore are continuously measured during the shut-in and reopening operations of a well. After removing temperature effects, extensional strain changes can be observed at locations around the perforation cluster during a shut-in period. We interpret that the observed strain changes are caused by near-wellbore fracture aperture changes caused by pressure increases within the near-wellbore fracture network. The depth locations of the measured strain changes correlate well with distributed acoustic sensing (DAS) acoustic intensity measurements that were measured during the stimulation of the well. The shape and magnitude of the strain changes differ significantly between two completion designs in the same well. Different dependencies between strain and borehole pressure can be observed at most of the perforation clusters between the shut-in and reopening periods. We assess that this new type of distributed fiber-optic measurement method can significantly improve understanding of near-wellbore hydraulic fracture characteristics and the relationships between stimulation and production from unconventional oil and gas wells.

Abstract A good cement-casing bond is essential for effective zonal isolation in both active and abandoned wells. A new method was developed to monitor the cement-casing bond in real-time and in-situ using a fiber optic distributed temperature and strain sensing (DTSS) system. To demonstrate the concept, the DTSS system was used in a laboratory-scale well model, which has a fiber optic cable installed helically on the outside surface of a steel pipe that served as a model for a casing string. A cement annulus was created by placing the steel pipe with the optical fiber into a larger PVC pipe. The DTSS system successfully captured strain changes at the cement-casing bond due to an axial load applied on the casing. The helical wrapping installation enabled circumferential measurements of temperature and strain changes in the entire cement annulus. The results were used to evaluate the risk of cement debonding by estimating the shear stress in the fiber and by comparing it to the shear strength of the cement bond. In addition, the effect of embedding a fiber optic cable on the hydraulic integrity of cement annulus was also evaluated using a gas permeability test. The permeability of cement samples with embedded fibers was found to be elevated compared to plain cement samples without fibers, but the permeability values were well within accepted industry limits. Compared to existing cement bond logging tools, the proposed fiber optic sensing system can provide continuous, real-time and in-situ monitoring of the cement bond and zonal isolation in either active or abandoned wells, without the need for wellbore entry. The system can serve as an early warning system to identify, and possibly prevent, the loss of a cement barrier, by providing detailed information (i.e. location, type, and severity of an event(s)) that will facilitate any remedial operations, if necessary.

Abstract Subsurface geomechanical changes can cause severe damage to oil and gas well casing strings and cement barriers, which can compromise the zonal isolation of either an abandoned or active well, in the latter case jeopardizing its productive life. A novel system was developed based on laboratory experiments to simultaneously monitor casing deformation and cement integrity using fiber optic distributed temperature and strain sensing (DTSS). The proposed system consists of a hybrid-Brillouin-Rayleigh-based DTSS technique used in combination with two dedicated fiber optic cables. The first is a standard telecommunication fiber, which is used to measure strain changes due to casing deformation. The second cable, coated with a hydrocarbon-sensitive polymer, detects an additional strain caused by the presence of hydrocarbons due to a loss of zonal isolation. The combined system can also detect temperature changes caused by formation fluid invasion from a lower depth into the cement annulus. Since the two cables will be installed side-by-side on the outside of a casing string within the cement sheath, the system can also be used for monitoring the quality of a cementing job. The proposed system provides continuous, real-time and in-situ monitoring of casing deformation and cement integrity to prevent substantial impact on production, or to detect plug failure and hydrocarbon leakage for abandoned and decommissioned wells. It can thereby provide detailed information (i.e. location, type, and event severity) to plan and execute remedial operations, if necessary.

This paper presents an advanced fiber optic distributed temperature and strain sensing (DTSS) system designed for real-time in-situ monitoring of cement presence and integrity in the annuli of an oil and gas well. The DTSS system is used to monitor cement quality and zonal isolation by application of hybrid Brillouin and Rayleigh technology. This sophisticated technology allows for separate strain and temperature measurements using a single optical fiber. The DTSS system enables monitoring of the exothermic cement hydration reactions after a cement slurry is displaced into an annular space and allowed to set. In the laboratory, temperature and strain profiles were measured using the DTSS system at various external temperatures to quantify the effect of heat release during cement hydration. The temperature measurements showed excellent agreement with those obtained from thermocouples embedded in the same cement samples for comparison. Contamination of cement due to incomplete displacement of drilling fluid by cement slurry was also considered in the experiments. Contamination with synthetic-based drilling fluid was found to decrease the amount of heat generated during the cement hydration reactions. The degree of cement hydration and the presence of cement in the annular space - or lack thereof - can therefore be quantified. It is shown that the temperature profiles measured using the DTSS system can be used to detect both the top of cement (TOC) as well as annular sections that are either left uncemented or contaminated with drilling fluid. In addition to monitoring cement hydration, specially designed fiber optic sensing cables were developed to detect the presence and migration of hydrocarbons in cemented annuli, which may occur either because the cement is absent or compromised by cracking/fracturing. The fiber optic cables were modified with hydrocarbon-sensitive coatings generating a swelling effect when exposed to hydrocarbons. Such swelling effect could be measured and quantified using an induced strain on the fiber optic cable, which is monitored and recorded by the DTSS system. The modified cable was also evaluated for its response to various well construction fluids (such as synthetic based drilling fluid, spacers etc.). The ability to monitor cement hydration and hydrocarbon presence behind casing using cement-embedded fiber optic sensors that provide real-time, continuous responses without the need for wellbore re-entry presents a powerful new tool to assess and verify the quality of zonal isolation over the entire lifecycle of the well.

The directly obtained output from Distributed Optical Fiber Sensing (DOFS) system is strain, while control parameters in majority of engineering applications are defined in terms of displacements. This paper introduces general three-dimensional (3D) shape and displacements monitoring method by means of distributed optical fiber sensing combined with appropriate fiber installation scheme. The displacement precision as a function of strain precision, resolution, and sensing fibers configuration are mathematically established in a simple equation. The results of the actual monitoring project are also provided to further illustrate the effects of the proposed approach. Three types of available DOFS systems, namely Brillouin Optical Time Domain Reflectometry (BOTDR), Pulse-Pre-Pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) and Tunable-Wavelength Coherent Optical Time Domain Reflectometry (TWCOTDR), each with precision an order of magnitude better than the other, are compared to highlight their influence on obtained displacement precision. Millimeter-order precision required in tunnel, bridge, or railway tracks monitoring applications, for distance over several kilometers, are possible with TW-COTDR, while BOTDR measurements cannot provide any valuable information.

Abstract Cement displacement efficiency significantly affects the quality of a well cementing job. Inefficient displacement of drilling fluids by spacers and cement slurry results in poor placement and potential contamination of the cement, which in turn can compromise cement integrity and threaten zonal isolation of oil and gas wells. In this paper, a novel method is introduced to monitor the cement displacement process in real time using fiber optic distributed temperature and strain sensing (DTSS) technologyas drilling fluid, spacer and cement are pumped through the casing annuli.An advanced DTSS system, based on hybrid Brillouin and Rayleigh backscattering, was used in combination with a specially designed fiber optic cable to identify the location of each fluid (i.e. drilling fluid, spacer fluid and cement slurry) during the cement displacement process. The fiber optic cable consists of a single-mode optical fiber packaged with a polymer that has selective sensitivity to various well construction fluids, and thus can be used to detect the presence of each fluid. Both strain and temperature changes were monitored by the DTSS system to track the cement displacement process. When the proposed fiber optic cable was exposed to synthetic-based mud (SBM) and spacer fluid, the strain values recorded by the fiber differed by a few orders of magnitude. When the cable is exposed to cement slurry, the location of cement can be determined from its exothermic heat release signature, which is apparent in both strain and temperature measurements. Contamination of cement slurry with drilling fluid was found to have a significant impact on the strain and temperature profiles. Thus, the DTSS system can provide useful information regarding top of cement (TOC), the wait-on-cement (WOC) time and the displacement efficiency in real time. Cement displacement of drilling fluids and spacer fluids has been modeled in the past; however, to date the displacement process and the locations of these fluids have never been tracked and verified in real time. This paper presents a new way for real-time, in-situ, continuous, and non-disruptive monitoring of the cement displacement process and tracking of the well construction fluids.

Abstract This paper presents an advanced fiber optic distributed temperature and strain sensing (DTSS) system designed for real-time in-situ monitoring of cement annuli in an oil and gas well. The DTSS system used in this study of cement quality and zonal isolation uses both Brillouin and Rayleigh backscattering phenomena, allowing one to separate strain and temperature using a single optical fiber. The first part of the paper focuses on monitoring the exothermic cement hydration process after a cement slurry is displaced into an annular space. In the laboratory, temperature and strain profiles were measured independently using the DTSS system and thermocouples at various temperatures to quantify the effect of heat release during cement hydration. These independent temperature measurements showed excellent agreement. Contamination of cement due to incomplete displacement of drilling muds by cement slurry was also simulated in the experiments. Contamination was found to decrease the amount of heat generated during the cement hydration process. The degree of cement hydration and the presence of cement in the annular space – or lack thereof - could thereby be quantified. It is shown that the temperature profiles measured using the hybrid-DTSS system can be used to detect both the top of cement (TOC) as well as annular sections that are either left uncemented or contaminated with drilling fluid. This is highly relevant information, because contamination of cement is one of the main factors that negatively affects zonal isolation directly by creating paths for hydrocarbon migration or indirectly by weakening the cement, making it susceptible to damage from cyclical pressure/temperature loads. In addition to monitoring cement hydration, specially designed fiber optic sensing cables were used to detect the presence and migration of hydrocarbons in cemented annuli, either because the cement was absent or compromised by cracking/fracturing. The presence of hydrocarbons in cemented annuli could be detected even after the cables were exposed to well construction fluids such as synthetic-based drilling mud and spacer fluid. Moreover, the materials used were sensitive to the type of hydrocarbon, allowing indirect hydrocarbon fingerprinting and determination of the origin of the hydrocarbons behind pipe. This presents a powerful new tool to assess the quality of zonal isolation behind casing, with the ability to monitor in real-time over the entire lifecycle of the well. In this capacity, it may provide guidance on such important decisions as the need for well intervention and remedial cementing.