Abstract:

Single-well seismology, reverse vertical seismic profiles (RVSP's) and crosswell seismology are three new seismic techniques for obtaining much higher resolution images of oil and gas reservoirs than what is currently obtainable with surface seismic techniques. Borehole seismology involves inserting both the source and the seismic receivers in oil or gas wells. In the past these methods have been limited to short distances between source and receivers in shallow wells. In 1997 a new borehole seismic source and receiver system has been deployed with a capability of handling source--receiver spacings of more than 2000 m in rock with a Q value of more than 20, and well depths as great as 6500 m. This advanced borehole seismic data acquisition system consists of a powerful, clamped, swept-frequency, vibratory source which is nondestructive, a multilevel receiver string of clamped, three-component geophones, and an acquisition system for reverse VSP's. The downhole vibrator produces high-quality S waves, with controlled polarization, as well as P-wave direct arrivals and reflections. This paper discusses the design and performance of this system.