Low-Frequency Drill Bit Seismic While Drilling

Abstract

Abstract A breakthrough has been discovered for controlling seismic sources to generate selectable low frequencies applicable to many seismic applications. All possible borehole pulsed sources, including hydraulically driven devices, explosives, and etc., by their very nature produce high frequencies. This is counter to the need for long transmission through rock. Specifically, we are reporting the application of an otherwise high frequency sparker source on the drill string for Drill Bit Seismic While Drilling (SWD). The low frequency source provides real-time imaging in deep (15,000 feet+) high-temperature (150°C) high-pressure (HTHP) wells ahead of the bit for accurate pore pressure determinations and geosteering, reservoir model verification, and near wellbore diagnostics. Furthermore, to have additional energy available at the drill bit can result in increased rates of penetration. Introduction It has been said, " The time is coming when we will not drill without looking ahead of the bit anymore than we would drive at night without headlights - occasionally shining a lamp to see what we hit.?? An alternative seismic source for the roller bit as it was being replaced by the PDC bit is something oil and service companies have sought since the early 1990's. A breakthrough has been discovered for controlling seismic sources to generate selectable low frequencies (< 40 Hz) applicable to many seismic applications. All possible borehole pulsed sources, including hydraulically driven devices, sparkers, explosives, etc., by their very nature produce high frequencies. This is counter to the need for long distance transmission through rock. Specifically, we have demonstrated the application of an otherwise high frequency sparker source which can be encorporated into a drill bit for Drill Bit Seismic While Drilling (SWD). The low frequency source, capable of creating selectable mid-band frequencies of 1 to 20 Hz, provides a source to perform real-time imaging in deep (15,000 feet+), high-temperature (150 degrees C), high-pressure (HTHP) wells for (a) geosteering, (b) accurate seismic hole depth, (c) accurate pore pressure determinations ahead of the bit, (d) near wellbore diagnostics with a downhole receiver and wired drill pipe, and (e) reservoir model verification. Furthermore, to have additional energy available at the drill bit for rock desintergation can result in increased rates of penetration.