3D-VSP Survey Using a DAS System and Downhole Geophone Array in Southwest China

Abstract

Summary Fibre optic Distributed Acoustic Sensing (DAS) is a novel technology that uses an optical fibre cable as a sensor array for acoustic signals and one can take almost any downhole fibre-optic installation or deployment and turn the fibre optic cable into a large downhole seismic array to provide enhanced VSP imaging and monitor fluids and pressures changes in the hydrocarbon production reservoir. Seismic imaging and time-lapse reservoir monitoring can give us critical information to guide the placement of production and water injection wells in high-value reservoirs. In order to obtain the characteristics of a shallow shale gas reservoir in Southwest China and to overcome the difficulties of low coverage and difficult imaging of shallow target layers with 3D surface seismic data, a simultaneous acquisition project of 3D surface seismic and 3D-VSP data was implemented in Zhejiang Oilfield, and the DAS technique was used in the 3D-VSP data acquisition. This paper takes the 3D DAS-VSP project as an example to introduce the data quality of DAS acquisition, and the technique for signal to noise ratio improvement in 3D DAS-VSP data processing. The difference between common fibers and armored fibers has been focused on to discuss the possibility of DAS system's industrialization.