Borehole geophysics

[BH-02] DAS 3DVSP Survey at Stratigraphic Test Well (Hydrate-01)

★ Invited

*Akira Fujimoto¹, Teck Kean Lim², Kyojiro Kawaguchi¹, Machiko Tamaki³, Toshiaki Kobayashi¹, Timothy S. Collett⁴, Seth S. Haines⁴, Ray Boswell⁵ (1. Japan Oil, Gas and Metals National Corporation (Japan), 2. Toyo Engineering Corporation (Japan), 3. Japan Oil Engineering Co., Ltd. (Japan), 4. U.S. Geological Survey (United States of America), 5. National Energy Technology Laboratory, U.S. Department of Energy (United States of America))

We present acquisition, processing, and interpretation of the known largest onshore 3D Vertical Seismic Profile (VSP) survey acquired with a single-mode fiber optic cable. This survey was carried out to detect the distribution of faults near the methane hydrate research well (Stratigraphic Test Well: Hydrate-01). The data was recorded with a Distributed Acoustic Sensor (DAS) cable cemented behind the casing. The cable was installed in 2018 and the 3DVSP survey was carried out in the first quarter of 2019. A total of 1701 shot records were successfully acquired in 12 days using a DAS interrogator with two vibroseise trucks sweeping simultaneously. The recorded data was high quality and contained broad band frequency energy up to 180 Hz. The data was converted from strain rate to geophone equivalent for data processing. The traveltime tomography was carried out using first break of all shots to build a TTI velocity model. The standard VSP processing such as editing, denoise, upgoing/downgoing wavefield separation and VSP deconvolution were applied. Then a 3D pre-stack depth migration using the upgoing wavefield and the velocity model created by the traveltime tomography was performed to output a 3DVSP volume. Faults around the well were interpreted using the 3DVSP volume and its attributes. The faults were clearly observed in the 3DVSP volume although they cannot be recognized by an existing 3D surface seismic volume. The faults interpreted by the 3DVSP volume were reflected into a 3D geological model and also used to determine locations of producer wells for the production test.