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

Abstract

Abstract The super-giant ACG field lies in the Azerbaijani sector of the south Caspian Sea. Since the signing of the "Contract of the Century" in September 1994, the significant complexity of the geohazards setting over this field has required near continual acquisition of geophysical imagery to better understand the various geohazard issues faced. Upon signing of the PSA it was known that there was very little geophysical imagery of the shallow section in existence. As such, the first geophysical operation over the PSA contract area in 1995 was a blanket regional 2D survey of the entire 450km2 PSA contract area to allow regional geohazards mapping to be undertaken. This entailed acquiring a regional grid of HR2D seismic data and a seabed survey that included collection of swath bathymetry. The challenges of importing acquisition systems into Azerbaijan, and mobilizing the equipment onto vessels of opportunity, limited the systems that could be used at the time. Therefore, the bathymetric model that was produced, for example, was useful, but limited by a swath bathymetry system that could only image to ~210m of water depth while PSA contract area water depths vary between 96 and 425m. Over the following decade, geophysical site investigations of appraisal wells, platform sites and pipeline routes followed industry norms of site specific 2D surveys. However, in 2004, one pass HR3D and seafloor surveys were acquired making use of a 3D seismic vessel. The use of the larger vessel had various advantages. Firstly, the capability to safely tow four streamers and two sources allowed acquisition of eight lines of subsurface coverage per sail-line. Secondly, the more stable vessel platform, allied with a more robust design of over-side mountings, provided a far superior platform for acquisition of swath bathymetry data. The resulting seabed and sub-seabed imagery were far superior to preceding imagery. In 2007, another step change in data quality was achieved with the acquisition of the first ever deep-water AUV survey acquired in the Caspian Sea. Using a Hugin 3000 vehicle, the resulting swath bathymetry, sonar and sub-bottom profiler imagery saw another step change in quality. HR3D and AUV data of the entire PSA have now been acquired in a phased approach. Included in the HR3D acquisition were undershoots of the six producing platform complexes to verify the integrity of overburden conditions below the platforms. This paper will show the improvements in data quality that have been achieved over life of the PSA, and demonstrate the impact these improvements have had on better understanding of geohazards for future development and ongoing operations across the field.