Suppression of Seismic Interference Noise on Gulf of Mexico Data

ABSTRACT Seismic data recorded in the Gulf of Mexico is often contaminated with interference from the energy sources of other vessels operating in the same area. These interfering waves exhibit coherent noise patterns with linear move out. Usually, they have very high amplitudes. If they are not suppressed prior to disconsolation, they cause poor spectral balancing of the data. They can easily survive the stacking process despite its power in the suppression of a variety of noise types. We have developed a new noise suppression technique to apply at the earliest stage of processing. It is based on a noise-pick-reduction scheme; which, first forms reference traces from interference-free shot records, then discriminates high-energy interfering events by comparing the RMS levels of the seismic traces with those of the reference traces, and finally, attenuates them by a multiplier determined from the RMS levels. In this paper, we summarize the results of our investigation of the seismic interference noise problem and the development of SILVER, a new method to suppress high amplitude noise events. INTRODUCTION Seismic interference from the other energy sources has become a severe problem in recent Gulf of Mexico surveys. Amplitudes of these interfering waves are often higher than acceptable levels in the industry. Solution of this problem during data ~acquisitions is limited to a scheduled time-sharing plan. If this plan is not strictly carried out by all the parties operating in the same area, the interference noise can cause substantial downtime in operations. Therefore, we have analyzed the seismic interference noise problem, and developed a new technique to suppress the noise events in processing. THE SEISMIC INTERFERENCE NOISE PROBLEM Seismic interference from the other energy sources appears as coherent noise events on records. Figure 1 illustrates a shot record from a survey in offshore Louisiana and Mississippi over the Upper Continental Crust. Review of all the profiles on this survey indicates that approximately one third of them are contaminated with the seismic interference noise. Measured peak-to-peak amplitude and RMS level of the interfering energy on this record is 35 and 5.35 microbar respectively. A 4800% CDP gather on which the relative amplitudes are preserved, is displayed on Figure 2. An RMS energy plot is shown on the right side of the figure. RMS values are calculated for a sliding time window of 200 mess length. Interference noise events are clearly identified on both sections with their high energy levels. Seventeen traces of this particular gather are contaminated with the interference noise after 5 seconds. Noise events are randomly distributed within the section. They are disordered since interference noise has different arrival times on each shot record. Our study of the gathers show that these random patterns are repeated with Out change except that they are shifted laterally and towards later times. Traces that are contaminated with the seismic interference noise have quite different autocorrelation estimates than the others.