Head of Team : Dr. Wahyu Triyoso

Team Members : Prof. Satria Bijaksana and Silvia Jannatul Fajar, MT.

Lake Towuti sediment deposits have special feature in reconstruct the basin formations. It lies on ophiolitic rock of East Sulawesi Opihiolites. Seismic reflection survey was used to reveal the subsurface sedimentary of the lake. Surface related multiple elimination (SRME) and predictive deconvolution were used to increase seismic resolution and attenuate the presence of long and short period multiples. Rough analysis of the seismic facies reliable to distinct the sediment into 2 units. Unit 1 shows continuous and parallel sediment reflectors, while unit 2 have discontinuous and chaotic reflectors. Two intersection seismic profiles in the deeper part in the northeastern sub-basin shows that this basin is bordered by normal and strike slip fault. The fault can be traced to the surface and its extension can be aligned with the topographic lineament.

Data and Method

Three seismic acquisition type, include “CHIRP”, single and multi-channel data were acquired to get the best places for taking the drilling site in Towuti Lake. Noise and seismic multiples from shallow sediment target in the lake occurs and need to be removed. Predictive deconvolution and Surface related Multiple Elimination (SRME) methods were used to remove the presence of the long and short period multiples. Predictive deconvolution filters are usually designed examining the autocorrelations of traces prior to deconvolution (Peacock and Treitel, 1969) . Key parameters of predictive deconvolution for multiples suppression are predictive distance (n) and operator length.

(α) (Yilmaz, 2001) as shown in equation 1. The prediction distance is generally set equal to estimates of multiple period while operator length is often set approximately equal to wavelet length (Lines, 1996).

Surface-related multiple elimination (SRME) was applied in three steps (Verschuur and Berkhout, 1997). The first step includes the removal of all non-physical noise, regularization of the measured data to obtain a constant grid of source and receivers, interpolate the missing near offset and intermediate offset, and the removal of the direct wave and its surface reflection. The second step is the prediction of multiples, and the third step is subtracting predicted multiples from input data.

Result and Discussion

Predictive deconvolution and SRME were applied to a 2D multichannel seismic line from Towuti Lake. The data severely contaminated with multiples that are generated by surface multiple and intrabed multiple. These multiples had been suppressed by using the above methods and shows better seismic section for interpretations (Figure 1 and 2). The seismic section shows 2 major units that can be distinguish by its reflectors (figure 3). Unit 1 shows continuous and parallel sediment reflectors, while unit 2 have discontinuous and chaotic reflectors. Two intersection seismic profiles in the deeper part in the northeastern sub-basin shows that this basin is bordered by normal and strike slip fault. The fault can be traced to the surface and its extension can be aligned with the topographic lineament.

Conclusions

Multiple suppression using predictive deconvolution and SRME shows better result. The long and short period multiples can be attenuated by using accurate parameters. The seismic section interpretation shows 2 major units according to facies. The fault through the seismic line gave big influence below the unit 1 horizon.

References

• Lines, L., 1996, Suppression of shot period multiplesdeconvolution or model based inversion, Canadian J. of exploration geoph, 32, 63-72.
• Peacock, K., and treitel, S., 1969, Predictive deconvolution: theory and practice, Geophysics Prosp, 34, 155-169.
• Verschuur, D. J., and Berkhout, A. J., 1997, Estimation of multiple scattering by iterative inversion, Part II: Practical aspects and examples, Geophysics, 62, 1596-1611.

• Vogel, H., Russell, J., dan Bijaksana, S., Cahyarini, S., Wattrus, N., Rethemeyer, J., dan Melles, M. (2015): Depositional modes and lake-level variability at Lake Towuti, Indonesia, during the past ~29 kyr BP. Journal Paleolimnology.
• Yilmaz, O., (2001): Seismic Data Analysis: Processing, Inversion, and Interpretation of Seismic Data. Society of Exploration Geophysicists, Tulsa.