Leendert Combee

Over/under towed-streamer acquisition A method to extend seismic bandwidth to both higher and lower frequencies

Seismic resolution of towed marine-streamer data is affected by free-surface reflections. They strongly modulate the spectrum reducing energy at the so-called notch frequencies, fn = iv/2z {i = 0,1,…,∞}, in which v is the water velocity and z is the source or receiver depth. As a result there is a very strong loss of useful low-frequency energy and usually a similar loss at higher frequencies. The ghost effect occurs both at the source and at the receiver. At the source, the upgoing part of the source wavefield is reflected off the free surface with inverted polarity before its delayed journey into the Earth. At the receiver, the upgoing part of the receiver wavefield is reflected off the free surface with inverted polarity before it travels down to the receiver again. The over/under acquisition method allows separation of the up- and downgoing wavefields at the source (or receiver) using a vertical pair of sources (or receivers) to determine wave direction. In this article, we present the results of two ...

Acquisition of marine point receiver seismic data with a towed streamer.

Summary A new concept for the acquisition of point receiver towed streamer data is introduced. Recording of point receiver data, rather than the analogue outputs of hardwired arrays, enables both dynamic group forming and enhanced attenuation of noise. Dynamic group forming allows better signal preservation and enhanced frequency recovery, particularly at far offsets. Data adaptive noise attenuation methods allows improved attenuation of the low frequency noise induced by water flow around the streamer, enabling the enhancement of the low frequency signal-to-noise ratio through avoidance of low cut filters. Point receiver marine seismic data will improve the dynamic range of the seismic signal and enhance the viability of time-lapse monitoring of reservoirs with towed streamer data.

Acquisition of Highly Repeatable Seismic Data Using Active Streamer Steering

Summary At the 62nd meeting of the European Association of Geoscientists and Engineers, in Glasgow, a new system for marine seismic cable steering and control was described (Bittleston et al., 2000). In this paper, recent operational experience with this system is reported. Seismic data acquired using active streamer steering, to achieve repeat positioning, is demonstrated to be highly repeatable.

Quantifying the Horizontal Vector Fidelity of a Marine Multicomponent Acquisition System

Summary In this paper, we demonstrate how we have quantified the vector fidelity of a marine multicomponent acquisition system using different metrics applied to data from various acquisition geometries. We find that the system performs to expectations with typical linearity variations of less than 1% and gain mismatches between the horizontal components of less than 10%. Analysis of converted-wave arrivals demonstrates excellent measurements of shearwave splitting consistent with other measurements of azimuthal anisotropy in the locality.

Scattering of the source‐generated wavefield by a Z‐D near‐surface elliptic anomaly

The problem of time-domain scattering of the source generated wave field by surface anomalies is considered. By taking an elliptic half-cylinder as the model for the surface anomaly, the symmetry properties of the configuration allow an explicit solution in terms of elliptic wave functions. This problem can be used as a semi-analytical test case for numerical modelling codes. Here, particular attention is paid to the validity of the conventional statics approximation that is generally in use to compensate for the traveltime variations. Our numerical results show that besides the expected change in travel time (static shift), a significant change in the wave field pulse shape FORMULATION OF THE PROBLEM