Method and device for separating seismic signals from seismic sources

A method for processing seismic data indicative of formations of subsurface, the seismic data being generated by actuating first and second marine acoustic sources in a firing sequence, the firing sequence including at least a first actuation of the first source followed by a first actuation of the second source followed by a second actuation of the first source and a second actuation of the second source, the method comprising:

• recording with receivers seismic waves reflected from the subsurface, wherein the reflected seismic waves originate from the first and second sources being towed and activated at substantially a same depth under water;
• determining in a processor, based on (i) a series of reference time instants, (ii) a variable first time delay relative to the series of reference time instants at which the first source is activated, and (iii) a variable second time delay relative to the series of reference time instants at which the second source is activated, two data sets corresponding to the first and second sources;
• and
• determining an image of the subsurface based on the two data sets,
• wherein time intervals between consecutive activations of the first and second sources are variable,
• wherein the series of reference time instants is calculated based on an assumption that no other source except the first source is present and thus there is no need for a waiting time necessitated by the actuation of the other source before firing again the first source, and time intervals between any two consecutive reference time instants are fixed to a predetermined value, and
• the first and second sources have a substantially same inline position.

A computing device configured to actuate first and second marine acoustic sources in a firing sequence, the firing sequence including at least a first actuation of the first source followed by a first actuation of the second source followed by a second actuation of the first source and a second actuation of the second source, the computing device comprising:

• an interface configured to receive information that the first source is towed at a depth in water substantially equal to a depth of the second source;
• and
• a processor connected to the interface and configured to,
• establish a series of reference time instants,
• actuate the first source with a variable first time delay relative to the series of reference time instants, and
• actuate the second source with a variable second time delay relative to the series of reference time instants such that time intervals between consecutive activations of the first and second sources are also variable,
• wherein the series of reference time instants is calculated based on an assumption that no other source except the first source is present and thus there is no need for a waiting time necessitated by the actuation of the other source before firing again the first source, and time intervals between any two consecutive reference time instants are fixed to a predetermined value, and
• the first and second sources have a substantially same inline position.

A computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor, implement a method for actuating first and second marine acoustic sources in a firing sequence, the firing sequence including at least a first actuation of the first source followed by a first actuation of the second source followed by a second actuation of the first source and a second actuation of the second source, the method comprising:

• towing the first source at a depth in water substantially equal to a depth of the second source;
• establishing a series of reference time instants;
• actuating the first source with a variable first time delay relative to the series of reference time instants;
• and
• actuating the second source with a variable second time delay relative to the series of reference time instants such that time intervals between consecutive activations of the first and second sources are also variable,
• wherein the series of reference time instants is calculated based on an assumption that no other source except the first source is present and thus there is no need for a waiting time necessitated by the actuation of the other source before firing again the first source, and a time interval between any two consecutive reference time instants is fixed to a predetermined value, and
• the first and second sources have a substantially same inline position.