Seismic-while-drilling (SWD) is a new service that is intended to optimize drilling programs with respect to target depth uncertainty and unanticipated drilling hazards. Similar to vertical seismic profiling (VSP) in scope – but a real-time measurement – SWD applications include aiding the driller in placing the bit on a target identified via surface seismic reflection data (Fig. 1), estimation of anomalous subsurface velocity far ahead of the bit, and high-resolution subsurface imaging. As this information is provided in near realtime, drilling decisions such as setting coring and casing points, hazard avoidance, and over-pressure zone identification are greatly facilitated by SWD technology. SWD developments are part of a recent trend to incorporate an increasing number of the measurements that have been traditionally made by wireline-conveyed sensors into the logging while drilling (LWD) drillstring in order to increase the timevalue of those measurements. SWD can potentially be done in at least two distinct ways — using a downhole source (active or drill bit) and surface receivers; or by using an active seismic source on the surface and one or more receivers downhole. The early commercial SWD services were based on the former. In more recent SWD developments, downhole receivers are employed with a surface source. Since drilling noise contaminates the frequency band of the seismic signal, data are acquired during a “quiet” period of the drilling operation and not while drilling activity is taking place. Measurements are often made at stand changes with little or no interruption of the standard drilling workflow. The newly developed next-generation tool (Fig. 2) for real-time seismic recording while drilling combines the deployment of multiple multi-axis sensors, including ruggedized triaxial geophones, seismic-grade accelerometers, and hydrophones, with a novel, highly accurate clock and contingent surface systems. This paper investigates the performance of the new tool design and presents the results of field tests in which seismic data were acquired in various types of formations, and in vertical as well as deviated boreholes. The data acquired while drilling are compared to baseline commercial wireline VSP measurements in order to verify that the service provides data accuracy comparable to that of a standard commercial wireline.
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