Abstract: Methods and apparatus are described for the seismic exploration of strata adjacent to a borehole, wherein an arrangement of geophones is lowered into the borehole and clamped to the wall. The geophones are clamped at essentially equal angular distances along the circumference of the borehole. A plurality of such arrangements can be positioned along the longitudinal axis of the borehole. By combining the outputs of the geophones noise signals generated by symmetric guided waves are attenuated. The arrangement can be used for cross-well seismic acquisition and in combination with seismic sources and/or attenuator so as to form an single-unit exploration tool for borehole seismics.

Abstract: A method of seismic exploration while drilling from within a borehole containing fluid, with a source and receivers positioned in the borehole is provided, comprising detecting small amplitude signals from waves within the fluid. The method is used to identify signals from waves within the fluid known as tube waves that result from compressional waves converted at the bottom of the borehole. The invention also includes seismic detection apparatus comprising ring hydrophones or similar pressure sensors. The apparatus is preferably attached to a coiled tubing with the drill bit actuated by a separate actuator as source.

Abstract: Described is a finite-difference methodology for efficiently computing the seismic response from a seismic model subject to several changes within sub-volumes. Initially, the response from an original model is calculated and the wave field is recorded at receivers and along closed surfaces around the sub-volumes. As changes occur, the recorded seismograms can be updated by simulating the response on small models encompassing the immediate neighborhood of the regions of change, the recording locations, and the parts of model that contribute to subsequent reflections and scattering recorded at the receivers. The recorded wave field can then be added to the reference wave field to obtain the seismic responses of alterations to the model without having to recalculate the full altered model.

Abstract: The method includes the steps of applying a local spatial trigonometric transformation to seismic data to generate transformed data and compressing the transformed data. Compression may be achieved by retaining a selected part of the transformed data at reduced accuracy. The selected part may be a high frequency part of the transformed data. A window function is chosen so that the transformations are applied over a central window and overlap with the adjoining windows. Suitable transformations for use with the method include a local cosine transformation, a discrete cosine transformation of type IV, a local sine transformation and a Fourier transformation. For example, a HF part of the transformed data is retained at reduced accuracy. The transformed data is compressed by a coarser re-quantization of the transformed data. A temporal transformation is applied to the seismic data, that is local and of the trigonometric type.

Abstract: A method of attenuating multiples in signals recorded during a marine seismic survey is described using a multi-component data set of the survey and summing selected components of the data set after filtering components with a filter that combines recorded data from more that one receiver location and operates indiscriminately on P- and S-wave data.

Abstract: A method for determining a representation of an anisotropic earth formation is described, wherein the inversion step for generating the representation from recorded seismic data is performed using several values of a pre-defined anisotropy parameter addition to components of the moveout velocity. The anisotropy parameter is preferably introduced into the moveout equation or dispersion relation, which in turn is used in the inversion process.

Abstract: A method for using S-waves recorded at sea floor to determine anellipticity relating to at least one rock substrate is provided. In particular the method comprises identifying an S-wave event in recorded pre-stack seismic data and then determining at least one anisotropy parameter by adjusting moveout of a corresponding modeled S-wave event to agree with moveout of the identified S-wave event. The method is particularly applicable to mode converted S-waves in seismic signals.

Abstract: Methods and apparatus are described for seismic signal acquisition utilizing an odd number of vibratory sources arranged in line and positioning the sources for one sweep cycle at positions occupied by other sources during the previous sweep cycle. The method has advantages in particular for marine seismic acquisitions.

Abstract: Methods and apparatus are described for identifying and removing noise from borehole telemetry signals. A spectrum of the signal and of an approximated noise-free spectrum of the signals are generated and compared so as to identify frequencies at which noise occurs. The approximated spectrum is preferably generated by an averaging or integrating process which essentially results in a smoothened variant of the signal spectrum. The comparison includes dividing the signal spectrum by the approximated spectrum, and setting a threshold in the resulting dimensionless peak spectrum. The remaining parts of the peak spectrum are identified as noise. The dimensionless spectrum is found to have major advantages when having to identify noise frequencies.

Abstract: A marine seismic survey is described which uses measurements made in a mid-field region of the source signature to correct an estimate of the far-field source signature as derived from individual contributions of the seismic source elements. The technique reduces the effects of perturbations which else have a considerable impact on the estimation of the far-field.

Abstract: The signature of an energy source is determined from an inverse scattering Born series representing multiple reflected energy. The series comprises a polynomial in the inverse of the signature and has recorded data as the first term. The series is truncated, preferably to the first two terms to permit an analytical determination of the signature to be found. The value of the inverse signature which minimises the energy represented by the sub-series is found and this corresponds to the desired source signature. An iterative scheme may be adopted to improve the match to the actual signature so as to take into account the errors caused by truncating the scattering series.

Abstract: Methods and apparatus are described for reducing the multiple energy in seismic signal acquisitions, in particular for sea bottom acquisition. The method is based on the scattering Born series for free-surface multiples. It is characterized in that only terms of the even sub-series of the scattering Born series are considered for determining the multiple-free data.