USE OF MULTIBEAM BATHYMETRY AND BACKSCATTER TO IMPROVE SEABED GEOCHEMICAL SURVEYS: PART 1, HISTORICAL REVIEW, TECHNICAL DESCRIPTION, AND BEST PRACTICES

Abstract

Oil and gas seeps have been a key tool in hydrocarbon exploration since ancient times. Basin-wide reconnaissance exploration, focused on basic geology and identification of hydrocarbon seepage, has been typical of onshore basin analysis since the beginning of the petroleum industry. Since the discovery of marine chemosynthetic “cold seep” communities in the mid-1980s, and their association with offshore oil and gas seepage, the energy industry has been mapping seeps both to target them for exploration and avoid them in development. For exploration, the successful sampling of oil or gas at the seafloor reduces exploration risk by demonstrating generative source rock, maturation, migration, and charge – all key data about the subsurface petroleum systems. In the marine environment, seep communities and associated diagenetic precipitates can modify the bathymetry and/or the backscatter and can be imaged by Multibeam Echo Sounding (MBES). MBES can provide detailed bathymetry of the seafloor; multibeam backscatter can provide not only potential targets for seep sampling, but information on the seafloor characteristics at or just below the seafloor; and multibeam Water Column data can image gas plumes rising from the seafloor. Multibeam was introduced outside of military applications in the 1970’s, with the application of multibeam to seep science in the oil and gas industry, and the use of USBL-positioned cores in a real-time GIS to target seeps, began in the late 1990s, with the first proprietary survey in 2000. We review the history of multibeam, the history of seep science, and “lessons learned” over decades to best practices in seep hunting, from vessel specification to dry dock to pre-survey to survey operations to target selection.