Walkabove VSP with seismic-while-drilling technology: flawless operation in a highly deviated well

Abstract

SWD was recently used in the North West Shelf of Australia to acquire time-depth measurements and to obtain a vertical seismic profile (VSP) while pulling out of hole. The use of SWD technology greatly enhanced the understanding of geology by acquiring a more precise geophysical picture of the subsurface, leading to better understanding of the subsurface and placement of wells in the future. A vertical incidence VSP was acquired in an offshore deviated well for a client on the Australian North West Shelf. The data was acquired using a moving-surface source, suspended from a boat, and a four-component downhole sensor in the bottom hole assembly (BHA). The downhole data was acquired using three orthogonal geophones and a single hydrophone measurement at each VSP level. This was recorded while pulling out of hole, and processed once the tool was on surface. Time picking accuracy of the downhole data is ±0.5 ms with the frequency range 6–90Hz, both comparable to Wireline. The repeatability of the hydrophone and geophone time picks was also excellent with the average difference being 0.2 ms and maximum 0.8 ms. High resolution VSP images beneath the well in addition to corridor stacks were derived from the geophone and hydrophone data, showing the geological structure of the reservoir. The quality of the data acquired allowed the client to remove the need for a wireline VSP run; it, therefore, saved significant rig time and costs associated with it, reduced the chances of getting stuck, and significantly reduced the seismic uncertainty.