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Red Sea 2-D Transition Zone Seismic Data Acquisition: Challenges and Solutions

Musser, James A.1; Al-Omar, Waleed *1; Al-Amri, Mohammed 1; Lafon, Stephen K.1; Arifin, Mustajar 2
(1) Exploration Operations, Saudi Aramco, Dhahran, Saudi Arabia. (2) Coastline Geophysical Saudi Arabia Ltd., Al-Khobar, Saudi Arabia.

The Red Sea transition zone (TZ) is a very difficult area for seismic acquisition. Lines traverse mountains on the land portion, and then cross erratic marine bathymetry with water depths of up to 1,300 meters within a short distance from the shore. Surface features include rugged topography, populated areas, sabkhas, mangroves and coral reefs. Red Sea TZ operations require a novel approach for safe and efficient acquisition with special care given to this unique environment.

The primary objective of this project was to image deep sediments below salt bodies. Secondary objectives were shallower structural and stratigraphic targets. Two acquisition geometries were used for each TZ line; a symmetric split spread on the marine side with very long offsets for the deeper objectives, and an asymmetric split spread on the land side with somewhat shorter offsets landward as the targets become shallower. High fold data were acquired with both geometries and the two shooting patterns merged smoothly with continuous coverage without interruption.

Two independent systems were utilized to acquire seamless profiles. For the first time, a cabled land and offshore bottom cable (OBC) system was integrated with an autonomous node system for continuous 2D seismic recording. The project used five types of sources and four different types of receivers. Vibrators and impulsive sources were used on land, while very shallow air guns, small shallow air gun arrays and larger deep air gun arrays were used in the marine areas. In all cases, careful HSE measures were followed to ensure safe operations without environmental risk. Geophones, marsh phones, dual sensor stations and four-component point-receiver nodes were used as the receivers.

The nodal system was used in water depths greater than 50 m, beyond the water depth limit of the dual sensor OBC system used by this crew. Extreme and rapidly varying bathymetry necessitated the use of the cableless node system. The autonomous nodes were strung together using ropes with fixed intervals to facilitate deployment, positioning and retrieval. Once deployed, the two independent recording systems were used to simultaneously record the data from the different seismic sources across all terrains. While node systems inherently record common receiver gathers, and cabled systems record common shot gathers, the data from both systems were transcribed and combined in processing to create continuous, seamless shot gathers across all terrains.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain