Chevron Research Company

Chevron Research & Technology Company

William J Ostrander

Earl F Herkenhoff

Clint W Frasier

A method for improving the seismic resolution of geologic structures is disclosed. Refracted wave arrivals are gathered into common midpoint trace gathers. Data representations originating inside a critical offset distance are muted, and the remaining data is tau-P summed and projected into zero source-to-receiver offset. Constant velocity stacks can then be displayed. A plurality of common midpoint trace gathers can be used to generate multiple panels of tau-P sums. Portions of several of these panels can be combined to provide a complete image of the subsurface reactors. A near-surface velocity model can then be designed, to provide a solution to near-surface statics in seismic traces.

Method of improving the seismic resolution of geologic structures

The present invention indicates that in exploration of permafrost regions of the world for oil and gas accumulations, flexure noise can be attenuated by careful placement of the vibratory source vis-a-vis the receiver array during collection of the Vibroseis.RTM.-type data. If the explorationist adopts a survey strategy in which the vibratory source is separated from the receiver array by a pressure ridge or its equivalent over the ice formation of the region under survey, then - surprisingly - the seismic reflection signals can be easily collected and displayed. Result: continuity of events from onshore reflectors can be easily followed offshore through the transition zone into deeper sea ice regions. He is aided in formulating his exploration strategy by the use of aerial and/or radar photographs or LANDSAT unmanned satellite data for mapping the pressure ridges of the area under survey.

Method of attenuating sea ice flexure noise during seismic surveys of

The present invention indicates that in exploration of permafrost regions of the world for oil and gas accumulations, flexure noise can be attenuated by careful placement of the vibratory source vis-a-vis the receiver array during collection of the Vibroseis.RTM.-type data. It has been surprisingly found that if the explorationist adopts a survey strategy in which the vibratory source is separated from the receiver array by a pressure ridge or its equivalent over the ice formation of the region under survey, then the seismic reflection signals can be easily collected and displayed. Result: continuity of events from onshore reflectors can be easily followed offshore through the transition zone into deeper sea ice regions.

In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by displaying difference envelopes of 'near' and 'far' amplitude vs. time traces of each gather, as a function of common groups of centerpoints. A significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, such as hydrocarbon-bearing potential and/or lithology of the reflecting horizon.

Method for the interpretation of envelope-related seismic records to

In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by emphasizing the degree of amplitude variation between traces of each gather along a seismic line, and after generating semblance coefficients, displaying the resulting 'weighted' offset traces or representations of such traces as function of either horizontal offset or centerpoint values. A significant --and progressive --change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, say the fluid hydrocarbon-bearing potential and/or lithology of the reflecting horizon.

Method for the interpretation of statistically-related seismic records

The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast (with the overburden rock) has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within a gather of data) indicates the lithology of the reflecting horizon and the capping strata. Thus, lithologic determinations of high-intensity anomalies of gas-containing media is simplified: (i) progressive increases in amplitude intensity of resulting traces generated by the field array as a function of offset between respective source-detector pairs, can be associated with high porosity sandstones; underlying impervious shales; and (ii) progressive decreases in amplitudes of likewise commonly gathered traces, is associated with medium-to-low porosity lime-stones underlying a similar type of shale.

Method for interpretation of seismic records to yield indicating of the

In accordance with the present invention, progressive changes in amplitude as a function of offset of common gathers can be more easily identified by emphasizing the degree of amplitude variation between 'near' and 'far' amplitude vs. time traces of each gather along a seismic line, and displaying the resulting near and far offset sections side-by-side. A significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence (within sections) indicates valuable characteristics, say the fluid hydrocarbon-bearing potential and/or the lithology of the reflecting horizon.

Method for the interpretation of seismic records to yield valuable

The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast with the overburden rock has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence occurs. Thus, differentiating between high-intensity amplitude anomalies of nongas- and gas-containing media is simplified: progressive change in amplitude intensity of resulting traces generated by the field array as a function of offset between each source-detector pair, is associated with the last-mentioned medium only.

Method for interpretation of seismic records to yield indication of

The present invention indicates that gas-containing strata of an earth formation have low Poisson's ratios and that the acoustic contrast with the overburden rock has a surprising effect as a function of the angle of incidence on a seismic wave associated with an array of sources and detectors: viz., a significant--and progressive--change in P-wave reflection coefficient as a function of the angle of incidence occurs. Thus, differentiating between high-intensity amplitude annomalies of nongas- and gas-containing media is simplified: progressive change in amplitude intensity of resulting traces generated by the field array as a function of offset between each source-detector pair, is associated with the last-mentioned medium only.

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Benicia, CA, United States of America

William J Ostrander