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.