Demonstrations of Real-Time Borehole Seismic from an LWD Tool

Abstract

Abstract A new technique provides conventional borehole seismic measurements in real time while a well is being drilled. The system consists of a logging-while-drilling (LWD) tool with seismic sensors positioned near the drill bit, a seismic source at the surface, and a measurement-while-drilling (MWD) system for real-time telemetry. The seismic source is fired during pipe connections, seismic data are processed downhole and check-shot information is sent to the surface. Borehole seismic tools conveyed by wireline cable have been used for a variety of applications including seismic time-depth mapping, and reflection and transmission imaging of subsurface structures. Although wireline borehole seismic services are mature, they are unable to provide all the benefits that are sought in real time while drilling. This is particularly the case when borehole seismic surveys are conducted to help make drilling and well construction decisions, such as steering and deciding on casing and coring points. The new service provides standard borehole seismic information in real time that can be exploited for drilling optimization, cost savings, and safety improvements. Check-shot (time/depth) data are used to place the bit on the seismic map to help well navigation and casing point selection and to avoid drilling hazards, such as pore pressure, seen on the seismic. Real-time seismic velocities can be used to update pore-pressure predictions from surface seismic. Ultimately, the real-time velocities will be combined with look-ahead images, formed from the seismic reflections from horizons ahead of the bit, to provide a direct measurement of the distance to a marker of interest. In 2000, a field-test campaign conducted with experimental tools in the Gulf of Mexico demonstrated the first known real-time check-shot technique with an LWD tool. We will show the results and further describe the status of the service.