3D OBC Seismic Survey Parameters Optimization for a Carbonate Field Offshore Abu Dhabi, United Arab Emirates

Abstract

There is no doubt that 3D seismic data make a powerful contribution to field development. Less obvious, and often controversial, is the critical step of defining level of seismic survey effort required to achieve the objectives for field development. An over-specified seismic survey could be costly, and an under-specified seismic survey would not achieve the objectives. A 3D OBC pilot seismic survey was conducted in a carbonate field of offshore Abu Dhabi, United Arab Emirates with the main objectives: (1) to demonstrate imaging of the Upper Jurassic Arab formation; and (2) to optimize survey parameters for future seismic surveys. In this highly-specified pilot seismic survey, two orthogonal 3D datasets were acquired, and one swath 3D dataset was simulated by sampling shot-points parallel to receiver-lines. The data density is significantly different among these datasets, however the offset and azimuth distributions are similar. Twenty-three cubes were generated from these datasets by decimating the full data. Unless particular reasons necessitated change, the same processing parameters were applied to all cubes to minimize any differences due to processing effects. The relationship between data quality and operational effort was determined by analyzing twenty-three cubes qualitatively and quantitatively from the structure interpretability point of view. The main findings are: (1) higher specification cubes successfully imaged the main Upper Jurassic Arab reflectors; (2) higher specification cubes require higher operational effort; (3) in general, higher specifications improve data quality; (4) however, data quality eventually reaches a plateau even with increasing specifications; and (5) certain cubes are more efficient, they provide higher data quality with lower operational effort. The methodology and results will be used to assist in establishing and optimizing survey parameters for future seismic surveys offshore Abu Dhabi, United Arab Emirates.

3D OBC Seismic Survey Geometry Optimization Offshore Abu Dhabi, U.A.E.

“…It is not always easy to image the reflectors, especially in the Upper Jurassic succession, due to the very low acoustic impedance contrast. Ishiyama et al (2008) discussed 3D OBC seismic survey parameters for a specific survey in the region, based on the results of a feasibility study and a pilot survey, which can effectively and efficiently meet our geophysical requirements: (a) orthogonal geometry with receiver point and source point intervals of 25 m, receiver line and source line intervals of 200 m, wide azimuth sampling, nominal fold of 240 in the natural bin size (12.5×12.5 m) at the maximum inline offset of 3200 m corresponding to the nominal fold of 300 in the natural bin size at the maximum inline offset of 4000 m, namely OR2B in the Ishiyama's table; or (b) areal geometry with parallel swath shooting with receiver point interval of 25 m, shot point interval of 50 m, receiver line interval of 400 m, source line interval of 50 m, wide azimuth sampling, nominal fold of 480 in the natural bin size (12.5×25 m) at the maximum inline offset of 3200 m corresponding to the nominal fold of 600 in the natural bin size at the maximum inline offset of 4000 m, namely SW4A in the Ishiyama's table.…”