Method For Electromagnetic Prospecting Waveform Design
AssigneeExxonMobil Upstream Research Company
InventorScott C. Hornbostel
Life of this patent
Estimating the term…
Abstract
A waveform design method is presented for controlled source electromagnetic surveying. A desired source spectrum (82) is specified based on a desired resistivity depth image resolution (81) with spectral amplitudes determined by expected noise levels (83). Techniques are disclosed for designing a source waveform to match the desired source spectrum. When better resolution is desired at a target zone, this leads to a required clustering of frequency components. A modulated waveform can be used to provide this clustering of frequency components.
Claims17
A method for prospecting for hydrocarbons in a subsurface region using the results of a controlled-source electromagnetic survey, comprising:
- (a) obtaining measured electromagnetic data from a survey of the subsurface region, said survey having used at least one source waveform that was selected or designed by steps comprising:
- (i) defining a plurality of resolvable depth units within the subsurface region;
- (ii) for each depth unit, calculating an optimal frequency for penetrating to that depth;
- (iii) estimating noise levels at each optimal frequency;
- (iv) determining a minimum source amplitude at each optimal frequency in consideration of the estimated noise;
- and
- (v) selecting or designing at least one source waveform whose frequency spectrum, or combined frequency spectra if more than one source waveform, contains all optimal frequencies determined in (ii), within a pre-selected tolerance, with associated amplitudes substantially the same as or greater than the minimum amplitudes determined in (iv);
- (b) constructing an earth model of the subsurface region using electromagnetic data measured in the survey;
- and
- (c) predicting hydrocarbon potential of the subsurface region at least partly from the earth model.
A method for prospecting for hydrocarbons in a subsurface region using the results of a controlled-source electromagnetic survey, comprising:
- (a) conducting a controlled-source electromagnetic survey of the subsurface region, wherein said survey uses at least one source waveform that was selected or designed by steps comprising:
- (i) defining a plurality of resolvable depth units within the subsurface region;
- (ii) for each depth unit, calculating an optimal frequency for penetrating to that depth;
- (iii) estimating noise levels at each optimal frequency;
- (iv) determining a minimum source amplitude at each optimal frequency in consideration of the estimated noise;
- and
- (v) selecting or designing at least one source waveform whose frequency spectrum, or combined frequency spectra if more than one source waveform, contains all optimal frequencies determined in (ii), within a pre-selected tolerance, with associated amplitudes substantially the same as or greater than the minimum amplitudes determined in (iv);
- (b) predicting hydrocarbon potential of the subsurface region at least partly from an earth model of the subsurface region constructed using electromagnetic data measured in the survey.
Dependencies are inferred from the claim text.