Improving the Focus of the ACG Geohazards Image–20 Years of Data Acquisition

摘要

The super-giant ACG field lies in the Azerbaijani sector of the south Caspian Sea. Since the signing ofrnthe “Contract of the Century” in September 1994, the significant complexity of the geohazards settingrnover this field has required near continual acquisition of geophysical imagery to better understand thernvarious geohazard issues faced.rnUpon signing of the PSA it was known that there was very little geophysical imagery of the shallowrnsection in existence. As such, the first geophysical operation over the PSA contract area in 1995 was arnblanket regional 2D survey of the entire 450km~2 PSA contract area to allow regional geohazards mappingrnto be undertaken. This entailed acquiring a regional grid of HR2D seismic data and a seabed survey thatrnincluded collection of swath bathymetry. The challenges of importing acquisition systems into Azerbaijan,rnand mobilizing the equipment onto vessels of opportunity, limited the systems that could be used at therntime. Therefore, the bathymetric model that was produced, for example, was useful, but limited by a swathrnbathymetry system that could only image to ~210m of water depth while PSA contract area water depthsrnvary between 96 and 425m.rnOver the following decade, geophysical site investigations of appraisal wells, platform sites andrnpipeline routes followed industry norms of site specific 2D surveys.rnHowever, in 2004, one pass HR3D and seafloor surveys were acquired making use of a 3D seismicrnvessel. The use of the larger vessel had various advantages. Firstly, the capability to safely tow fourrnstreamers and two sources allowed acquisition of eight lines of subsurface coverage per sail-line.rnSecondly, the more stable vessel platform, allied with a more robust design of over-side mountings,rnprovided a far superior platform for acquisition of swath bathymetry data. The resulting seabed andrnsub-seabed imagery were far superior to preceding imagery.rnIn 2007, another step change in data quality was achieved with the acquisition of the first everrndeep-water AUV survey acquired in the Caspian Sea. Using a Hugin 3000 vehicle, the resulting swathrnbathymetry, sonar and sub-bottom profiler imagery saw another step change in quality.rnHR3D and AUV data of the entire PSA have now been acquired in a phased approach. Included in thernHR3D acquisition were undershoots of the six producing platform complexes to verify the integrity ofrnoverburden conditions below the platforms.rnThis paper will show the improvements in data quality that have been achieved over life of the PSA,rnand demonstrate the impact these improvements have had on better understanding of geohazards for futurerndevelopment and ongoing operations across the field.