Spatial frequency method and apparatus for investigating earth conductivity with high vertical resolution by induction techniques
AssigneeSchlumberger Technology Corporation
InventorThomas D. Barber
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Abstract
An electrical induction sonde for measuring a characteristic of an earth formation traversed by a borehole having improved vertical resolution and excellent depth of penetration. The sonde has two or more transmitter-receiver spacings preselected to provide at least two separate induction signals received from the formation that, when combined, produce a response function indicative of formation physical properties with no zeros in the spatial frequency response function over the frequency domain of interest.
Claims8
An induction sonde for measuring a characteristic of an earth formation traversed by a borehole comprising:
- a support member;
- transmitter means secured to the support member for transmitting an electromagnetic induction signal into said formation about the sonde;
- and
- receiver means secured to the support member a preselected distance from the transmitter means for receiving induction signals from the formation thereby determining the vertical response as a function of depth, the preselected distance being selected to provide a sonde with no zeros in the spatial frequency response in the frequency range of interest, said spatial frequency response being the Fourier transform of said vertical response.
The induction sonde of claim 8 in which the receiver means includes overlapped receiver arrays.
A method for determining a characteristic of an earth formation traversed by a borehole comprising the steps of:
- transmitting an electromagnetic induction signal into said formation;
- receiving induction signals form said formation thereby determining the vertical response of said formation;
- performing a Fourier transform of said vertical response thereby producing a spatial frequency response;
- and
- selecting a physical spacing of the transmitter and receiver elements transmitting and receiving said induction signals such that said Fourier transform of said vertical response produces a spatial frequency response having no zeros in the frequency range of interest.
Dependencies are inferred from the claim text.