3 research outputs found
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Real-time and post-hoc compression for data from Distributed Acoustic Sensing
Distributed Acoustic Sensing (DAS) is an emerging sensing technology that records the strain-rate along fiber optic cables at high spatial and temporal resolution. This technique is becoming a popular tool in seismology, hydrology, and other subsurface monitoring applications. However, due to the large coverage (10’s of km) and high density of measurements (1m spacing at 100’s of Hz), a DAS installation could produce terabytes of data records per day. Because many DAS instruments are deployed in remote locations, this large data size poses significant challenges to its transfer and storage. In this paper, we explore lossless compression methods to reduce the storage requirement in both real-time and post-hoc scenarios. We propose a two-stage compression method to improve the compression ratio and compression speed. This two-stage compression method could reduce the storage requirement by 40%, which is 20% more than other lossless methods, such as ZSTD. We demonstrate that the compression method could complete its operation well before the DAS instrument needs to output the next file, making it suitable for real-time DAS acquisition. We also implement a parallel compression method for a post-hoc scenario and demonstrate that our method could effectively utilize a parallel computer. With 256 CPU cores, our parallel compression method achieves the speed of 26GB/second
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Seismic monitoring of well integrity
Seismic tube waves, produced by flexure of the well boundary, pressure changes in the fluid in the well, and deformation of the material immediately surrounding the well, are particularly sensitive to variations in the state of the well. We evaluate a direct approach for generating and observing tube waves as a means of detecting well damage. While we find that it can be difficult to reliably excite observable tube waves without a very strong surface source, time-frequency techniques can be employed to increase the detectability of tube wave reflections. New technologies, particularly distributed acoustic sensing, hold great promise for evaluating well integrity by monitoring tube waves, temperature changes, and seismic noise due to well deformation and fluid leakage
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The EGS Collab -Experiment 2 Stimulations at 1.25 km Depth
The EGS Collab project is performing well-monitored rock stimulation and flow tests at the 10-m scale in an underground research laboratory to inform challenges in implementing enhanced geothermal systems (EGS). This project, supported by the US Department of Energy, is gathering data and observations from the field tests and comparing these to simulation results to understand processes and to build confidence in numerical modeling of the processes. Experiment 1 (now complete) examined hydraulic fracturing in an underground test bed at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, at a depth of approximately 1.5 km in a well-characterized phyllite. Geophysical monitoring instrumentation in six of eight sub-horizontal boreholes monitored stimulation events and flow tests. The other two boreholes were used to perform and carefully measure water injection and production. More than a dozen stimulations and nearly one year of flow tests in the testbed were performed. Detailed observations of processes occurring during stimulation and dynamic flow tests were collected and analyzed. Flow tests using ambient-temperature and chilled water were performed with intermittent tracer tests to examine system behavior. We achieved adaptive control of the tests using close monitoring of rapidly disseminated data and near-real-time simulation. Numerical simulation was critical in answering key experimental design questions, forecasting fracture behavior, and analyzing results. We were successful in performing many simulations in near-real-time in conjunction with the field experiments, with more detailed simulations performed later. The primary objective of Experiment 2 is to examine hydraulic shearing of natural fractures at a depth of 1.25 km in amphibolite at SURF. The stresses, rock type, and fracture conditions are different than in Experiment 1. The testbed consists of 9 boreholes, in addition to two earlier-drilled characterization boreholes. One borehole is used for injection, two fans of 2 monitoring wells have several geophysical measurement tools grouted in, and four open boreholes surrounding the injection hole are adaptively used for production and monitoring. We have encountered approximately five fracture set orientations in the testbed, and designed our testbed accordingly to maximize the potential for shear stimulation. Three stimulations have been performed to date from the injection borehole, each intersecting at least one production borehole. Different methods have been used for each stimulation, including a ramped flow, a high flow rate, and oscillating pressure