Patent EA-004776-B1 (EA)
Title: Method for multiple suppression based on phase arrays
Inventor: LEE PAUL J
IPC: G01V1/00
Filed: 2001-12-10
Abstract: 1. An apparatus for suppressing multiples in the collection of seismic data in a body of water with an air-water interface, comprising: at least one source of seismic signals positioned in the body of water; at least one receiver of seismic signals positioned in the body of water below the air-water interface and near the sources; a bubble diffuser positioned in the body of water so that the bubbles emitted by the bubble diffuser are positioned between the receivers and the air water interface, said bubble diffuser being configured to create bubble layers that combine high acoustic reflection with depth variation, said depth variation being designed to reflect incident acoustic waves away from the receivers, and a control for activating the bubble diffuser during the collection of seismic data by the sources and receivers. 2. The apparatus of claim 1, further comprising: a support positioned in the body of water below the air-water interface and near the receivers and attached to the bubble diffuser; and a towing line attached to the support for the bubble diffuser for positioning the emitted bubbles between the receivers and the air-water interface. 3. The apparatus of claim 1, further comprising: a compressed air hose for supplying compressed air to the bubble diffuser sufficient to emit bubbles providing high acoustic reflection. 4. The apparatus of claim 1, wherein the bubble diffuser comprises a plurality of diffuser elements. 5. The apparatus of claim 4, wherein the diffuser elements are ceramic stone air diffusers. 6. The apparatus of claim 4, wherein the diffuser elements are porous hose air diffusers. 7. The apparatus of claim 4, wherein the plurality of diffuser elements are positioned in a vertical orientation to increase bubble emission. 8. The apparatus of claim 4, wherein the plurality of diffuser elements are positioned in a horizontal orientation to increase bubble emission. 9. The apparatus of claim 8, wherein the plurality of diffuser elements comprise trailing porous air hoses. 10. The apparatus of claim 4, wherein the bubble diffuser comprises diffuser elements positioned in a vertically oriented phase grating. 11. The apparatus of claim 10, wherein the phase grating is focussed on a range of distances to the sources and receivers. 12. The apparatus of claim 10, wherein the diffuser elements of the phase grating are positioned according to a discrete number sequence. 13. The apparatus of claim 12 wherein the discrete number sequence is a primitive root sequence. 14. The apparatus of claim 10, wherein the diffuser elements of the phase grating are positioned in a generally concave upward shape. 15. The apparatus of claim 14, wherein the diffuser elements of the phase grating are positioned substantially in a wedge shape. 16. A method for suppressing multiples in the collection of seismic data in a body of water with an air-water interface, comprising the steps of: positioning at least one source of seismic signals and at least one receiver of seismic signals in the body of water, wherein the receivers are positioned below the air-water interface; bubbles, emitted by the bubble diffuser are positioned between the receivers and the air water interface, form a layer with high concentration of bubbles with different zones of bottom surface by depth to provide reflection of random acoustic waves from the receivers. 17. The method of claim 17, wherein the emitted bubbles are of sufficiently small size so that the bubbles rise slowly in the body of water. 18. The method of claim 16, wherein said depth variation is according to a discrete number sequence. 19. The method of claim 18, wherein the discrete number sequence is a primitive root sequence. 20. The method of claim 16, the lower boundary surface of the bubble layer is shaped generally concave upward in a cross-section perpendicular to the direction of seismic data collection. 21. The method of claim 20, wherein the concave upward shape is substantially a wedge shape.