Surveying techniques using multiple different types of sources

A system, comprising:

• one or more processors;
• and
• one or more memories having instructions stored thereon that are executable by the one or more processors to:
• access seismic data recorded using a plurality of seismic sensors during a transition survey, wherein the seismic data was recorded based on signals reflected from one or more geological structures in response to generating seismic signals using a first type of seismic source while also generating seismic signals using a second, different type of seismic source;
• and
• adjust, based on the accessed seismic data from the transition survey, sensor signals from at least one of a prior seismic survey that used the first type of seismic source or a subsequent seismic survey that used the second type of seismic source, wherein the adjustment calibrates one of the prior and the subsequent surveys with the other;
• wherein the transition survey comprised a 4D seismic survey relative to at least one of the prior seismic survey and the subsequent seismic survey, such that both the transition survey and the at least one survey employed seismic sensors spaced apart in an inline direction and in a crossline direction, and such that an elapsed time between the transition survey and the at least one survey was sufficiently long to allow detectable changes to occur in the geological structures between a time of the transition survey and a time of the at least one survey.

A non-transitory computer-readable medium having instructions stored thereon that are executable by a computing device to perform operations comprising:

• accessing seismic data recorded using a plurality of seismic sensors during a transition survey, wherein the seismic data was recorded based on signals reflected from one or more geological structures in response to generating seismic signals using a first type of seismic source while also generating seismic signals using a second, different type of seismic source;
• and
• adjusting, based on the accessed seismic data from the transition survey, sensor signals from at least one of a prior seismic survey that used the first type of seismic source or a subsequent seismic survey that used the second type of seismic source, wherein the adjusting calibrates one of the prior and the subsequent surveys with the other;
• wherein the transition survey comprised a 4D seismic survey relative to at least one of the prior seismic survey and the subsequent seismic survey, such that both the transition survey and the at least one survey employed seismic sensors spaced apart in an inline direction and in a crossline direction, and such that an elapsed time between the transition survey and the at least one survey was sufficiently long to allow detectable changes to occur in the geological structures between a time of the transition survey and a time of the at least one survey.

In a technological process in which images from a monitor seismic survey are generated for comparison with images from a baseline seismic survey to detect changes in subsurface characteristics, wherein the monitor survey occurs after the baseline survey, the specific improvement comprising:

• performing a transition survey using first and second different source types, the first type corresponding to a type used in the baseline seismic survey, and the second type corresponding to a type used or to be used in the monitor survey;
• determining differences between signals recorded from the first and second source types during the transition survey;
• and
• using the differences to adjust sensor signals from at least one of the baseline survey and the monitor survey, thereby enabling the generation of a monitor survey image and a baseline survey image such that differences between the images indicate changes in geological structures and not changes in seismic source types;
• wherein the transition survey comprises a 4D seismic survey relative to at least one of the baseline survey and the monitor survey, such that both the transition survey and the at least one survey employ seismic sensors spaced apart in an inline direction and in a crossline direction, and such that an elapsed time between the transition survey and the at least one survey is sufficiently long to allow detectable changes in the subsurface characteristics to occur between a time of the transition survey and a time of the at least one survey.

A method of performing 4D seismic surveying, comprising:

• accessing first seismic data corresponding to a first seismic survey over a location, wherein the first seismic survey was performed using a first seismic source type and not a second seismic source type;
• subsequent to the first seismic survey, performing a second seismic survey over the location to produce second seismic data, wherein the second seismic survey is performed using both the first seismic source type and the second seismic source type;
• subsequent to the second seismic survey, performing a third seismic survey over the location to produce third seismic data, wherein the third seismic survey is performed using the second seismic source type and not the first seismic source type;
• determining, based on the second seismic data, source difference data indicating differences attributable to source types and not to changes in geological structures associated with the location;
• and
• isolating changes in the geological structures that occurred between a time of the first seismic survey and a time of the third seismic survey, wherein the isolating comprises modifying, based on the source difference data, one of the first seismic data or the third seismic data;
• wherein the second seismic survey comprises a 4D seismic survey relative to at least one of the first seismic survey and the third seismic survey, such that both the second survey and the at least one survey employ seismic sensors spaced apart in an inline direction and in a crossline direction, and such that an elapsed time between the second survey and the at least one survey is sufficiently long to allow detectable changes to occur in the geological structures between a time of the second survey and a time of the at least one survey.