Resolution and Accuracy of Short-Offset Processed 3D Seismic Data for Seabed Mapping in Deep Water in Makassar Straits, Indonesia

Nenov, Nikolay¹; Paone, Francesco²; Marceglia, Andrea²; Ferris, Edward³
¹PT Geomahakarsa Indonesia, Jakarta, Indonesia.
²ENI Indonesia, Jakarta, Indonesia.
³PT Petroprima Geo Servis Nusantara, Jakarta, Indonesia.

This paper presents a case study from the ENI operated Muara Bakau (Jangkrik) PSC on the East Kalimantan shelf edge and the west slope of the Makassar straits. The paper discusses the resolution and accuracy of Short-Offset Processed 3D Seismic Data (SOPS) for seabed mapping and visualisation.

The utilisation of SOPS for seabed hazard evaluation in deep water has been steadily gaining popularity globally due to the following advantages illustrated by this case study:

Improved seabed relief resolution:
Continuing technological improvements in 3D seismic acquisition delivering datasets with increased lateral and vertical resolution. Datasets with 2ms sample interval and 6.25m x 12.5m bin size are becoming common. Vertical resolutions in the order of 1m at seabed are achievable. In deep water this level of seabed relief definition is better than the achievable by ship mounted multi beam echosounders (MBES). Better results can only be achieved by MBES operated close to the seabed as is the case with Autonomous Underwater Vehicle (AUV) mounted MBES.

High bathymetric accuracy:
In this paper the seabed Digital Terrain Model (DTM) derived from SOPS is compared to a DTM generated from AUV mounted MBES and to water depth measurements from drill rigs. The comparison shows that between 250m and 800m water depth the SOPS DTM accuracy is better than ±2m on average: better than IHO Survey Order 1a. Exceptions are areas of seabed slope greater than approximately 25°. In such areas the SOPS DTM accuracy is reduced due to position uncertainty of the interpreted seabed scarp edge.

Seabed seismic amplitude imaging:
The seabed seismic amplitude is colour coded and draped over the seabed DTM. The paper shows examples how this imaging can be used to interpret seabed lithologies. Seabed amplitudes can also be useful for the mapping of hydrocarbon seeps.

Large area coverage:
The ability to locate site specific geohazard analyses in a regional context and flexibility in case of problems with a chosen drilling site area. In the case of deep water field development the SOPS DTM can be used for preliminary design of seabed facilities and can thus reduce the time and cost for precision AUV surveys by limiting the AUV surveys to preferentially selected areas.

Relatively low cost:
Short-offset processed 3D seismic data is a by-product of the exploration data and has a much lower cost compared to an AUV MBES survey of the same area.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012