Advances in near-surface characterization and deep imaging with smart DAS upholes

Abstract

Abstract A smart distributed acoustic sensing (DAS) uphole system is proposed that utilizes a cost effective, permanently installed fiber as a seismic sensor embedded in the shallow subsurface. Using this system, uphole velocity surveys for near-surface characterization can be acquired with a single shot by recording all depth levels simultaneously. Dense grids of on-demand smart DAS upholes produce more accurate long-wavelength statics than conventional approaches, reducing uncertainty in the interpretation of low-relief structures. Connecting multiple upholes with a single fiber enables seismic surveys to be acquired with buried vertical arrays. These can provide robust images of the deeper subsurface like surface seismic, but with much improved accuracy due to the elimination of most of the near-surface complexities. The system comprising a carpet of surface shots and a dense grid of smart DAS upholes provides a complete dataset for near-surface characterization as well as imaging for oil and gas exploration of low-relief structures. The proposed smart DAS uphole acquisition scheme was successfully tested on an onshore field in Saudi Arabia. The field test demonstrates the validity of the components and the entire system. Smart DAS uphole data was found to be of excellent quality, while recorded seismic data with buried vertical arrays showed clear reflection signals and produced images of the deeper subsurface. This paper presents the smart DAS uphole system for near-surface characterization and deep imaging, including a discussion of the processing results from the data acquired during the field tests. We show how the novel acquisition system can be used in the petroleum industry to decrease the risks associated with the exploration of low-relief structures.