DAS VSP Using Hybrid Wireline Logging Cable in Deepwater Wells

Abstract

Abstract This work reports the results of two Vertical Seismic Profiles (VSP) in deep-water deviated wells in Brazil, acquired using Distributed Acoustic Sensing (DAS) as part of a hybrid wireline cable. DAS is an efficient alternative to acquire VSP surveys, especially in costly offshore environments (Hartog, 2017; Martinez et al., 2018). DAS embedded in hybrid optical-electrical cables, which utilizes the wireline as seismic recording element and so it leverages any logging intervention in a well to become a seismic run. A Zero-offset or rig-source VSP survey acquired with this technology can be recorded in matter of minutes, as opposed to it taking over 24hrs to record similar data with conventional tools (i.e., geophones). DAS seismic profiles are acquired while maintaining the logging cable stationary, so that a number of shots of the seismic source are taken to form a stack. Two DAS VSP jobs are described herein. One was acquired while lowering a sonic-caliper logging tool, while another job was acquired during a sidewall coring tool. Both jobs were acquired in less than 30 minutes and 50 shots to produce a stack. Excellent quality DAS data was recorded in both wells. In one of the wells, a conventional checkshot with sparse spatial sampling was recorded to compare velocity profiles against DAS. In both cases traditional well seismic products such as time-depth pairs, interval velocities, sonic calibration, corridor stack and migrated image and Q factor when applicable were obtained. For this reason, DAS can be an effective replacement of VSP acquired with traditional geophone methods in certain situations. The jobs here were the first deep-water, deep-target wells acquired successfully in the world with the technology of DAS in hybrid wireline cable. There were significant cost savings associated to the VSP operations using DAS, that came from reducing the rig time needed for their acquisition. A direct benefit of this technology is the reduction of the environmental footprint by both lowering noise emissions that disrupt marine ecosystems and, also carbon emissions that can be cut more than 90% over traditional VSP acquisition methods.