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Distributed Fiber-Optic Sensors Characterize Flow-Control-Device Performance

The complete paper describes piloting the collection and analysis of distributed temperature and acoustic sensing (DTS and DAS, respectively) data to characterize flow-control-device (FCD) performance and help improve understanding of steam-assisted gravity drainage (SAGD) inflow distribution.

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The complete paper describes piloting the collection and analysis of distributed temperature and acoustic sensing (DTS and DAS, respectively) data to characterize flow-control-device (FCD) performance and help improve understanding of steam-assisted gravity drainage (SAGD) inflow distribution. Fiber-optic-based instrumentation was deployed within FCD-equipped active wells using permanently installed coiled tubing. Logs were performed on multiple wells during stable and transient flowing conditions. Additionally, acoustic recording using flow-loop testing was completed with accelerometers, geophones, and fiber-optic cables during FCD characterization. The goal was to cross-reference the acquired acoustic signals for quantification of flow at devices and validation of performance. An overview of the flow-loop FCD acoustic characterization program is described.

Introduction

Installation of inflow control ­devices (ICDs) along SAGD production liners is common to enhance temperature conformance and accelerate depletion. Additionally, some operators advocate the installation of similar outflow control devices (OCDs) along the injection well of the SAGD well pair. Collectively, these inflow and outflow devices are often referred to as FCDs. Several FCD devices are commercially available for use in SAGD.

Methodology

In an effort to optimize FCD design and selection, a joint industry partnership (JIP) was formed and flow-loop testing conducted to establish FCD performance curves and erosion tolerance over wide pressure, temperature, and steam-quality ranges consistent with a typical SAGD well environment. In conjunction with flow-loop testing, several full-scale FCD deployments were completed at the JIP fields, including pilot wells at the production company’s SAGD facility. These wells were logged with fiber-optic technology.

Fiber-optic-based instrumentation was deployed within FCD-equipped wells using permanently installed coiled tubing. Well-architecture-design changes to a typical completion were not required because fiber-optic sensors are used for most non-FCD wells to collect DTS data. Although DTS is a common tool for optimizing SAGD production, it has certain limitations. Specifically, temperature changes along production wells typically do not allow a detailed definition or quantification of the inflow distribution along the wellbore.

In addition to DTS, DAS was performed periodically on the FCD wells. DAS logging of SAGD producers has several potential uses, including flow profiling, steam breakthrough or noncondensable gas (NCG) detection, multiphase flow characterization, electric submersible pump (ESP) performance, completion failure analysis, and 4D seismic analysis. Although FCD characterization with DAS appears promising, a knowledge gap exists regarding how to move beyond qualitative analysis to quantitative analysis of FCD performance and the lateral emulsion inflow distribution. Pending satisfactory results, DAS logging on active wells potentially can be completed to accelerate improvements of SAGD FCD performance and design as well as increase the efficiency of SAGD recovery through improved steam/oil ratio and an associated reduction in greenhouse gases.

The goal of the FCD JIP was to reduce potential risk of FCD deployments through a better understanding of the expected device performance and erosion resistance. At a minimum, gas identification with DAS is possible. From the perspective of a production engineer, understanding mechanisms for well damage and prevention are fundamental for a successful operation. Steam flashing or “zero subcool” at the liner can be achieved with DAS because of the high intensity of acoustic energy generated when multiphase flow exists at a device; this was proven with acoustic sensing at the service company and with field pilots.

The complete paper includes detailed discussion and illustration of laboratory testing and field pilots.

Laboratory Testing

A unique multiphase flow loop capable of replicating thermal, multiphase flow conditions that could occur in a SAGD production well was designed, constructed, and operated during a 6-year period to understand better how fluid flow is restricted through FCDs. While in the process of characterizing FCDs, the project scope was expanded to include investigation of the long-term reliability of FCDs using a new “FCD erosion loop.” This flow loop allowed FCDs to be subjected to accelerated particle impact erosion testing using water, quartz, and air injection.

After several FCDs had been characterized and eroded, the JIP identified improving interpretation of DAS data from SAGD producer wells as a fundamental focus area to continue progressing the implementation and optimization of FCD technology in SAGD. A service company provided a custom audio instrumentation and recording system set up parallel to the instrumentation and data-­acquisition system already present within the FCD characterization loop to capture the acoustic response of the FCDs during performance characterization. Fast Fourier transform spectral analysis was used to convert the audio recording from the time domain into the frequency domain so that the amount of acoustic energy within specified frequency bands with changing FCD operating conditions could be investigated. Initial laboratory test results were promising and have the potential to help operators understand DAS data from SAGD wells better.

The complete paper describes the test vessel and acoustic instrumentation.

Field Pilots

A service company began using DTS monitoring of a SAGD facility’s wells within the McMurray oil sands during 2012. The addition of DAS field testing to two pilot wells to enhance evaluation of inflow and FCD flow contribution took place during 2015. Several tests were executed to evaluate FCD performance and move the technology readiness level of the FCD application toward commercial acceptance. One of the field test wells was equipped with 31 liner-deployed FCDs (LDFCDs) equally spaced on every other joint. This pilot revealed the following important qualitative learnings and highlighted the potential of DAS instrumentation:

  • FCD design established on the basis of subcooled fluid (monophasic flow) is overly restrictive at multiphase SAGD conditions, which is expected to delay late-life, low-reservoir pressure recovery.
  • DAS plus DTS illustrated that DAS was able to identify steam flashing that DTS alone did not; therefore, DAS provides important well-integrity assurance.
  • DAS identified areas of heightened inflow on the basis of overall acoustic energy and frequency content, including an ability to define inflow rates qualitatively along the lateral and characterize the gas and liquid distribution. This provides helpful recovery guidance; however, further quantification of the lateral inflow distribution is desired.
  • DAS confirmed the integrity of the gas lift strings, which assists in understanding lift-efficiency challenges associated with low-drawdown inflow conditions.

The pilot well instrumentation consisted of a sealed 1-in. outer diameter (OD) instrumentation coiled tubing string containing single-mode fiber for DAS and multimode fiber for DTS. The fiber-optic strings were deployed inside a set of looped 0.25-in. capillary lines along with three duplex thermocouples. The fiber was deployed in situ by using the looped capillary lines to pump the fiber-optic lines into the capillaries (Fig. 1).

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Fig. 1—Instrumentation cross section.

 

The complete paper describes, illustrates, and presents results of field pilots for stable flow and rate modulation, analysis validation for pressure-drop correlation and spectral comparison, and transient analysis and calibration of FCD performance.

Conclusions

Although qualitative FCD analysis is possible, it remains unknown if an accurate quantitative FCD value can be derived with DAS. At a minimum, all data sets from pilots will be used as training to automate work flows and increase accuracy of qualitative analysis.

Continuous improvement of SAGD completions includes adoption and adaptation of FCDs. Application of specific FCDs requires ongoing development and testing in the laboratory and with field pilots. Specifically, FCD testing should be extended to include NCG and solvent recovery processes. Work completed by the JIP has confirmed DAS as a valuable incremental tool for qualitative analysis of FCD performance. The next steps for DAS monitoring applications include the following:

  • Developing and calibrating flow algorithms to quantify inflow on the basis of DAS, DTS, FCD design, production rates, and reservoir knowledge. To quantify inflow through FCDs, DAS can be used in combination with other measured and known parameters to estimate flow. Pressure drop and fluid composition, among other inputs, can be used to develop initial algorithms for quantifying flow. Collaboration is necessary to evolve algorithms and help improve accuracy. Algorithms should be designed for inflow quantification along the horizontal section of SAGD wells with FCD completions, specifically 7-in. LDFCDs and 4.5‑in. TDFCDs.
  • Performing DAS recordings on other FCD wells. To qualify how wells have evolved with respect to flow, understanding production during the life of the wells is important. This requires DAS to be measured several times during production. A baseline DAS data set during stable flow is relatively inexpensive to acquire and should be useful for future production optimization and algorithm development.
  • Quantifying FCD reliability through time and performing follow-up DAS acquisitions to confirm that FCDs are continuing to regulate inflow. Long-term performance is known in the laboratories but is limited in field verification to confirm reliability expectations relating to erosion, plugging, or other failure mechanisms.
  • Continuing the service company’s flow-loop testing to “fingerprint” FCDs to understand further frequency generation at FCDs in a flow loop that allows modulation of pressure drop, emulsion composition, and temperature across FCDs. A matrix of flow conditions can be recorded to create of a library of DAS signatures generated by FCDs.

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 195869, “Characterization of Flow-Control-Device Performance With Distributed Fiber-Optic Sensors,” by Ben Banack, SPE, Halliburton; Lyle H. Burke, SPE, Canadian Natural Resources; and Daniel Booy, SPE, C-FER Technologies, et al., prepared for the 2019 SPE Annual Technical Conference and Exhibition, Calgary, 30 September–2 October. The paper has not been peer reviewed.