Summary The first exploration-and-production downhole field trial of distributed acoustic sensing (DAS) fiber-optic technology was conducted during the completion of a tight gas well in February 2009. DAS is a novel technology that allows the detection, discrimination, and location of acoustic events on a standard telecom single-mode fiber several kilometers long. Using a combination of the measurement of backscattered light and advanced signal processing, the DAS interrogator system segregates the fiber into an array of individual microphones. To date, the technology has been applied mainly in the defense and security industries. One of the most exciting applications for downhole application of DAS is in the area of hydraulic fracturing of tight-sand and shale-gas reservoirs. Balancing the cost of hydraulic-fracture stimulation with the production benefit is crucial in tight-sand and shale-gas developments because, after drilling costs, the completion is the largest single cost component of the well. Recordings can be made while tools are run in hole, bridge plugs are set and perforations are shot and during the fracture-stimulation treatment. The technology is sufficiently reliable and sensitive to detect and monitor these in-well activities. The fidelity of the recordings made during hydraulic-fracturing and flowback operations provides a step-change improvement in the ability to perform real-time and post-job diagnostics and analyses of the stimulation. The different case studies presented in this paper will illustrate how, even in its earliest form, DAS has the potential to enhance the capability of monitoring and understanding in-wellbore activities. The technology enables the optimization of hydraulic-fracturing design and execution, which can drive down completion costs and lead to increased well productivity and ultimate recovery.
In order to make commercial and development decisions effectively and more rapidly, new appraisal and testing technologies are needed to maximize early data collection and subsequent subsurface understanding as quickly as possible. For Unconventional Gas and Light Tight Oil (UGLTO) projects, some of this critical data can be derived from hydraulic fracture stimulation and inflow profiling activities. For UGLTO projects, achieving an optimum hydraulic fracture stimulation is a continuous endeavor beginning as early as possible; and balancing the cost of completion vs. production performance is critical as the completion/stimulation is a large cost component of the well and heavily influences production rate/ultimate recovery. The fast paced development and introduction of new completion technologies requires diagnostic technology that can help us understand stimulation effectiveness, assess new completion technologies, and evaluate which zones are the most productive. One emerging technology, fibre optic distributed sensing has the potential of providing key insights during both the hydraulic fracturing and initial flowback. The passive nature of fibre optic sensors allows intervention-free surveillance, which makes fibre-optic technology an effective platform for permanent sensing in producing wells. Until recently, the oil & gas industry fibre optic sensing technology has focused mainly on temperature (DTS) profiling along the wellbore. In 2009, it was first demonstrated how fibre optic distributed acoustic sensing (DAS) can also be used for downhole applications. Where hydraulic fracture diagnostics based on DTS alone in the past sometimes yielded ambiguous results, the combination of both acoustic and temperature sensing provides a step-change improvement in the ability to perform real-time and post-job diagnostics & analyses of the stimulation. The different horizontal well case studies presented in this paper will illustrate how the combination of DTS and DAS has the potential to enhance the monitoring, assessment, and optimization of openhole and limited entry designed hydraulic fracture stimulation treatments.
The first E&P downhole field trial of Distributed Acoustic Sensing (DAS) fibre optic technology was conducted by Shell Canada during the completion of a tight gas well in February 2009. DAS is a novel technology that allows the detection, discrimination and location of acoustic events on a standard telecom single-mode fibre of several kilometres in length. Using a combination of the measurement of backscattered light and advanced signal processing, the DAS interrogator system segregates the fibre into an array of individual "microphones". To date the technology has been mainly applied in the defense and security industries. One of the most exciting applications for downhole application of DAS is in the area of hydraulic fracturing of tight sand and shale gas reservoirs. Balancing the cost of hydraulic fracture stimulation versus the production benefit is crucial in a tight sand and shale gas developments as, after drilling costs, the completion is the largest single cost component of the well. Recordings were made while tools were run in hole, bridge plugs set, perforations shot and during the fracture stimulation treatment(s). The technology proved sufficiently reliable and sensitive to detect and monitor these in-well activities. The fidelity of the recordings made during hydraulic fracturing and flow back operations, provided a step-change improvement in the ability to perform real-time and post-job diagnostics & analyses of the stimulation. The different case studies presented in this paper will illustrate how, even in its earliest form, DAS has the potential to enhance the capability of monitoring and understanding in-wellbore activities. The technology enables the optimization of hydraulic fracturing design and execution, which could drive down completion costs and lead to increased well productivity and ultimate recovery.
Summary Tight gas, low-permeability reservoirs offer a tremendous challenge with respect to effectively completing and draining a target reservoir. Openhole-packer completions in horizontal wells offer a cost-efficient means of accessing the entire lateral section, assuming the target pay can be effectively stimulated. The challenge with openhole completions compared with more-conventional cased, cemented, and limited-entry perforated completions is understanding and controlling hydraulic-fracture geometry—specifically, the number and location of fracture-initiation points and the fracturing-fluid flow into the near-wellbore (NWB) region of the reservoir. Fiber-optic-based distributed temperature sensing (DTS) offers a method for identifying, quantifying, and evaluating the NWB fracture geometry, the fracturing-fluid distribution in these broad openhole sections, and overall stimulation effectiveness. DTS can also reveal success or issues with respect to effective zonal isolation when using mechanical isolation during the hydraulic-fracturing process. In this particular case study, a lateral well in a basin-centered gas area was completed with swell-packer interval isolation by use of fracture sleeves for reservoir access. By coupling fracture-treatment responses and openhole log characteristics with the NWB DTS data during pumping and warm back, an integrated assessment of the completion stimulation effectiveness and efficiency was performed. The end result of this assessment provided an improved understanding of the current completion performance and allowed optimization of openhole completion projects for future wells in this same area.
Tight-gas, low-permeability reservoirs offer a tremendous challenge with respect to effectively completing and draining a target reservoir. Openhole-packer completions in horizontal wells offer a cost-efficient means of accessing the entire lateral section, assuming the target pay can be effectively stimulated. The challenge with openhole completions compared to more conventional cased, cemented, and limited-entry perforated completions is understanding and controlling hydraulic-fracture geometry; specifically, the number and location of fracture-initiation points and the fracturing-fluid flow into the near-wellbore (NWB) area of the reservoir. Fiber-optic-based distributed temperature sensing (DTS) offers a method for identifying, quantifying, and evaluating the NWB fracture geometry, the fracturing-fluid distribution in these broad openhole sections, and overall stimulation effectiveness. DTS can also reveal success or issues with respect to effective zonal isolation when using mechanical isolation during the hydraulic-fracturing process. In this particular case study, a lateral well in a basin-centered gas (BCG) area was completed with swellpacker interval isolation using fracture sleeves for reservoir access. By coupling fracture-treatment responses and openhole log characteristics with the NWB DTS data during pumping and warm-back, an integrated assessment of the completion stimulation effectiveness and efficiency was performed. The end result of this assessment provided an improved understanding of the current completion performance and allowed optimization of openhole completion projects for future wells in this same area.
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