Exploring difficult terrains with complex geology is challenging for any technology, particularly in frontier areas where regional reconnaissance is necessary. Potential field interpretation represents a strong support to extract correct geological information, in addition to that from geological and seismic data. We aim at using this information to build structural models related to the tectonic framework and basement configuration. Many exploration studies are based on source edge mapping analysis from gravity and magnetic data and several semiautomatic methods, based on the use of derivatives of the potential fields, have been developed. Most of these methods have been codified in commercial software, very intensely used in Oil & Gas Industry for exploration studies. We compare six methods of edge detection in the gravity case. Even though the success of each method depends on the quality of data and on the specific geological setting, co-locating the solutions from different methods may often provide an increased confidence in the reliability of a given edge location. A multiscale approach is however decisive in terms of meaningful mapping of source edges, since it provides the finest separation of edges from the largest to the shallowest of the allowed scales.
The Eni operated Muara Bakau (Jangkrik) Production Sharing Contract Block is situated on the East Kalimantan shelf edge and the west slope of the Makassar straits, Indonesia. Water depths vary from 70m on the shelf to 1000m at the east edge of the block. The steep shelf edge leads into a generally eroded and canyonized slope. Seafloor stability is an issue as evidenced by seabed slumping. Debris flows originating at the shelf edge may also pose a risk. In addition, shallow gas accumulations are present.
A study was undertaken to better understand the regional seabed morphology with respect to potential geohazards to field development. The methodology used provides a low cost alternative to dedicated Multi-beam Echo Sounder surveys and significant advantages over 2D High Resolution surveys for mapping the true areal extent of geo-hazards. Short offset data from a conventional 3D exploration seismic survey was reprocessed through two independent flows to yield high spatial and vertical resolution data suitable for accurate seabed mapping and near surface geohazard studies. The first customized reprocessing flow was designed to accurately image the seabed with high spatial resolution. Sun-illuminated 3D visualizations applied to the data aid analysis and interpretation of the seabed morphology. The second reprocessing flow was focused on the near surface section and includes generating data attributes of amplitude, coherency, and angle-versus-offset diagnostics for identifying shallow gas.
This methodology proved to be a powerful tool not only for investigating site-specific drilling hazards, but also for future field development planning. It consistently helped Eni to better select the location of subsea facilities and define the layouts of the development concept, to be further analyzed during the Concept Selection, which was presented with the submission of the Plan of Development in July 2011 and approved in November 2011.