Date(s) - 06/11/2019
11:30 am - 1:00 pm
Fiber Optic Microseismic Processing
Microseismic Monitoring is a principal method in monitoring and assessing the geometry of an unconventional completion. Data is recorded by an offset borehole seismic monitoring array or when the level of seismicity is sufficient the events can be detected and located from surface. Downhole monitoring has limitations in terms of well access including the cost of well preparation and deployment; surface monitoring likewise has limitations in terms of cost and the distance at which events can be detected and located.
Fiber optics (F/O) in the form of distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) has seen a rapid growth in its applications in recent years including long-term monitoring in industrial applications. In an unconventional completion a permanent installed fiber enables monitoring of flow over the life of the well including during the completion of an unconventional well. Techniques are also evolving for the temporary deployment of fiber in a well including fiber optic encased in a carbon rod allowing for deployment akin to coil tubing.
While the use of DAS for seismic acquisition is not entirely new, sensitivity has been a limitation in its application to Microseismic Monitoring. Here the technology continues to evolve with a continued improvement in DAS sensitivity. One component is the advancement of the lasers in interrogator units. In other F/O applications a driver of laser technology has been towards improving on distance, which has resulted also in an improvement in the sensitivity. Unlike for a geophone the sensitivity limitation in F/O are not yet at the limits of the physics; we can anticipate that the sensitivity of DAS will continue to improve.
The second challenge in the application of DAS for microseismic is in the processing and analysis of the data. One of the limitations is in that DAS is a single axis measurement as either strain or strain rate. In the case of a horizontal deployment we tend to predominantly observe a shear horizontal (SH) polarized arrival along with some component of the P-wavefield. As the measurement moves to the vertical this changes to the P-SV wavefield. In not having a full three component measurement we also cannot determine the direction of arrival beyond what can be resolved from the apparent velocity.
While partial information about the source can be inferred from a single fiber array the greatest potential is in having either multiple fiber array or a combination of fiber and conventional three component borehole seismic array. In addition to location there is also the possibility of resolving the source focal mechanism from multiple of measurements
In our presentation we will look at some recently acquired data including data recorded on multiple fiber array in combination with downhole three component array. We will look at some simple but effective ways to analyze the DAS data recorded over the extent of the wellbore. While the volume of data generated during continuous multi-well fiber acquisition can be significant the data is manageable with real-time Microseismic monitoring of a completion feasible.
Julian Drew is the Director of Microseismic Technology at Sigma Cubed Microseismic. He formerly worked at Schlumberger including Wireline Borehole Seismic, Engineering and in Research. He has been involved for more than ten years in Microseismic developing some of the key algorithms and software technology in use today at Schlumberger and at Sigma Cubed Microseismic. Julian received a dual BaSci (Physics) and BaEng (Mech) from the University of Western Australia, and a PhD (Geophysics) from the University of Cambridge.
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