Recent 4S High Fold 3D Seismic Acquisitions in the Abu Dhabi Foreland of the Oman Mountains

摘要

OMV and ADNOC commissioned WestemGeco to acquire a high fold, high density seismic program in the Foreland of the Oman Mountains, west of the city Al Ain. The objective of the survey was to acquire high quality 3D seismic data for a proper delineation and reservoir characterisation of structural and stratigraphic trapping geometries in order to identify potential exploration drilling locations. The acquisition commenced Mid-2014 and was completed by early 2015. The program included two separate 3D areas covering 1800km2. In addition, 700km of infill 2D lines were recorded to connect the two 3D surveys with modern 2D seismic and to complement the existing vintage 2D seismic grid. The seismic surveys were recorded with a Single Source Single Sensor design (4S) using WesternGeco's UniQ seismic acquisition system with single sensor geophone accelerometers (GACs) and single 80,0001b DX-80 vibrators. A Maximum Displacement Sweep was designed to enhance especially low frequencies resulting in a broadened amplitude spectrum. Operating up to 15 vibrators simultaneously allowed a very efficient seismic data acquisition but needed the implementation of the correct separations and slip times to ensure the data was not contaminated. The 18sec custom designed broad bandwidth sweep (1-120Hz) enhanced the S/N ratio in general and improved the data quality of the deeper target levels due to the input of low frequencies (below 10 Hz). Sufficient azimuth, high fold, long offsets, broad bandwidth as well as optimum random noise reduction and increased spatial resolution was required to improve data quality. Therefore gaining more value with advanced seismic attribute analysis and enhancing the illumination of deeper zones in order to meet the objectives of the seismic. On the logistical side, high flexibility was needed to allow complex and dynamic fleet grouping to maximize productivity. Any cross-talk noise between two different sources was managed using Managed Source and Spread (MSS) time and distance rules, which were based on the target characteristics. Acquiring dense 4S seismic required detailed planning to ensure operational safety and to achieve the planned fold coverage, especially in areas of dense infrastructure. The processing sequence for the high fold, high density 4S pre-stack seismic totalling 160 TB of data - 16 billion traces, was designed to effectively remove noise and preserve signal fidelity in the pre-stack data to ensure an optimal imaging and resolution of the geological targets. Due to the dune environment in the area, the application of optimal static solutions was an essential processing step. The good sampling of the noise in the raw data by the high density and high fold acquisition enabled a successful noise suppression performance and resulted in improving the image of the geological signal.