Seismic-While-Drilling Source for Real-Time Pore Pressure Prediction

60848 Deepwater drilling operations are subject to blowouts because formation gas pressures ahead of the bit are unknown. Seismic-while-drilling techniques can detect pore pressure ramps and range to pressurized formation tops, but, in most cases, the drill bit source is inadequate. There is a need for a source of broadband, high-frequency seismic energy at the bit to allow accurate seismic-while-drilling with all bit types. This project will develop a mud-powered hydraulic tool that generates intense narrow-band, high frequency seismic signals from tricone and PDC drill bits. The tool cycle rate can be swept to generate broadband seismic energy for vertical seismic profiling and reflection imaging while drilling. The objective is a real-time display of the formation 1000 ft ahead of the bit with a resolution of 50 ft. This display would indicate the range to reflection horizons, formation velocity gradients and predicted pore pressure. In Phase I, geophones placed on the surface were used to monitor the seismic signal transmitted to the surface from the suction pulse tool while drilling in a 2700 ft deep well. These experiments showed that the tool generates high levels of seismic energy at frequencies of up to 200 Hz while drilling with tricone and PDC bits. In Phase II, the hydraulic tool will be modified to continuously vary the pulse cycle rate through a full octave for broadband signal generation. Performance will be demonstrated during normal drilling operations, and the data recording, processing, and display techniques will be evaluated. Commercial Applications and Other Benefits as described by the awardee: Accurate seismic-while-drilling should reduce the economic, environmental and safety risks associated with deep gas exploration. Pore pressure prediction will allow more accurate casing placement and reduced costs and risks ¿ particularly in high-cost offshore and deep gas wells. Seismic-while-drilling also should increase deep well success rates by allowing steering into the productive zone.