3-C Fiber Optic Point Sensors Qualification for True Vector Wavefield Measurements at ASL Quarry in Cornwall

Summary A fixed offset VSP with dual airgun and vibrator sources was acquired in our test site at Rosemanowes ex. HDR (Hot Dry Rock) geothermal research site in the shallowest slightly deviated well RH7 in open hole as part our R&D program for downhole tool testing and qualification. The main intent was to use our 20 cu.in. airgun source in a fixed offset gun pit (∼94m from wellhead) and vibrator (∼108m from wellhead) to record a reference 3-C dataset where complex body waves kinematics in this Carnmenellis granitic geological environment were observed. The point sensor technology using high fidelity 3-C geophone is used for our vectorial receiver measurements reference dataset to be compared with our 3C fiber optic technology. This geometrical set up offers the possibility to record good VSP data to nearly ground level where broadside direct P-arrival is observed on the vertical component and where the horizontal components receive a good fraction of direct P-wave energy in the shallow section and hence the ability to quantify 3-C vector fidelity based on down-wave polarization method. Dual sources offered the possibility to evaluate the broadband signal outputs and validate isotropic coupling for all coherent signal frequency bands for direct P-wave polarization