Downhole seismic-sonic receiver
View Patent ↗A downhole tool for gathering formation data from inside a borehole includes a substantially tubular housing adapted for axial connection to a drill string and multiple sensors coupled to the tubular housing. The sensors include a first pair of sensors aligned along a first axis and adapted to measure a spatial derivative along the first axis, a second pair of sensors aligned along a second axis and adapted to measure a spatial derivative along the second axis, and a third pair of sensors aligned along a third axis and adapted to measure a spatial derivative along the third axis. In selected embodiments, the spatial derivatives are used to differentiate seismic or sonic compression and shear waves measured in a downhole environment.
1. A downhole tool for gathering formation data from inside a borehole, the downhole tool comprising:
a tubular housing adapted for axial connection to a tool string; and
a plurality of sensors coupled to the tubular housing and arranged at the corners of a rectangular prismatic shape, the plurality of sensors comprising:
a first pair of sensors aligned along a first axis, the first pair adapted to measure a spatial derivative along the first axis;
a second pair of sensors aligned along a second axis orthogonal to the first axis, the second pair adapted to measure a spatial derivative along the second axis;
a third pair of sensors aligned along a third axis orthogonal to the first and second axes, the third pair adapted to measure a spatial derivative along the third axis; and
diaphragms to flexibly couple the sensors to the tubular housing while rigidly coupling the sensors to a borehole wall.
2. The downhole tool of claim 1 , wherein the sensors are three-component geophones, each individual component of the three-component geophones aligned with one of three orthogonal faces of the rectangular prismatic shape.
3. The downhole tool of claim 1 , wherein the rectangular prismatic shape is a cube.
4. The downhole tool of claim 1 , wherein at least one of the first, second, and third pairs of sensors share a common sensor.
5. The downhole tool of claim 1 , wherein the sensors are selected from the group consisting of geophones, accelerometers, hydrophones, and vibrometers.
6. The downhole tool of claim 1 , wherein the spatial derivatives are used to differentiate compression and shear waves.
7. The downhole tool of claim 1 , further comprising at least one additional sensor to provide a conventional vertical-seismic-profile (VSP) signal.
8. The downhole tool of claim 1 , further comprising at least one additional sensor rigidly attached to the tubular housing to compensate for vibrations in the drill string.
9. A downhole drilling system for gathering formation data from inside a borehole, the downhole drilling system comprising:
downhole drill string;
source coupled to the downhole drill string, the source adapted to generate at least one of seismic and sonic waves; and
receiver coupled to the drill string and adapted to receive at least one of the seismic and sonic waves, the receiver comprising a tubular housing adapted for axial connection to a drill string and a plurality of sensors coupled to the tubular housing and arranged at the corners of a rectangular prismatic shape, the plurality of sensors comprising:
a first pair of sensors aligned along a first axis, the first pair adapted to measure a spatial derivative along the first axis;
a second pair of sensors aligned along a second axis orthogonal to the first axis, the second pair adapted to measure a spatial derivative along the second axis; and
a third pair of sensors aligned along a third axis orthogonal to the first and second axes, the third pair adapted to measure a spatial derivative along the third axis; and
diaphragms to flexibly couple the sensors to the tubular housing while rigidly coupling the sensors to a borehole wall.
10. The downhole drilling system of claim 9 , wherein the sensors are three-component geophones, wherein each individual component of the three-component geophones is aligned with one of three orthogonal faces of the rectangular prismatic shape.
11. The downhole drilling system of claim 9 , wherein the rectangular prismatic shape is a cube.
12. The downhole drilling system of claim 9 , wherein at least one of the first, second, and third pairs of sensors share a common sensor.
13. The downhole drilling system of claim 9 , wherein the sensors are selected from the group consisting of geophones, accelerometers, hydrophones, and vibrometers.
14. The downhole drilling system of claim 9 , wherein the spatial derivatives are used to differentiate compression and shear waves.
15. The downhole drilling system of claim 9 , further comprising at least one additional sensor to provide a conventional vertical-seismic-profile (VSP) signal.
16. The downhole drilling system of claim 9 , further comprising at least one additional sensor rigidly attached to the tubular housing to compensate for vibrations in the drill string.