A successful 3-D seismic survey over Bahrain Island

Abstract

ABSTRACT Environmental constraints are critical issues for land seismic operations and require the development of appropriate equipment and methods. In 1998, Compagnie Générale de Géophysique (CGG) acquired and processed seamless seismic data on behalf of the Bahrain Petroleum Company (Bapco) from a complex field on the Island of Bahrain. The operation ran smoothly in spite of the difficulty of working amongst pipelines, wells, and other oil and gas installations; scarps and sabkhas; urban areas; a zoo, golf course, and racecourse; an oil refinery and aluminum smelter; and other industrial and commercial facilities. The survey deployed a wide range of recording equipment including two sets of vibrators and a combination of radio and cable telemetry recording systems, and a fleet-management system. The successful completion of the survey was achieved through dedicated teamwork. The key elements were as follows: (1) collecting the correct baseline information; (2) detailed planning of the timeframe, human and material resources, adaptation of acquisition techniques to varying circumstances, and health and safety requirements; (3) continuous monitoring of external conditions and the impact of the operation on the environment, in full consultation with the appropriate authorities; (4) maximum flexibility in the field operations so as to allow for changing conditions and unforeseen events; and (5) close partnership between CGG and Bapco at all stages of the project. A joint CGG/Bapco team designed sophisticated processing methods, with top priority being given to the numerous surface heterogeneities. In particular, the recording of an intensive up-hole survey allowed a dedicated team at CGG in France to compute a robust subsurface model and a precise set of primary statics. Seven velocity layers from the Quaternary sandstone to the base of the calcareous and dolomitic Eocene were mapped. These showed significant lateral and vertical velocity variations within identified geological units. Surface-consistent signal processing with calibration to well data was used to compensate for the variations. Other critical processing steps included detailed velocity control, the application of dip moveout routines with acquisition-irregularity-compensation schemes, Radon demultiples and 3-D algorithms, designed for optimal de-noising and imaging. These combined efforts led to the delivery of a final 3-D migrated block. As a result, a complete reinterpretation of the area was possible that significantly increased the estimated recoverable oil reserves (particularly by-passed oil) in the Awali field.