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 450km 2 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.

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Imaging the giant Azeri and Chirag fields and the Deep Water Portion of the Gunashli field (ACG) in the Caspian Sea is a complex challenge. While the basic structure is a simple, large anticline, seismic imaging is hindered by a combination of mud volcanoes, shallow gas, complex overburden, high attenuation and multiples. Towed Streamer (TS) data successfully images some of the field, but significant uplift is seen on Ocean Bottom (OB) data.In this paper the results of 2D field trials are analysed to understand how cleaner and higher resolution images may be obtained. Several passes of a 2D line were acquired in the field trials, with varying acquisition configurations and, unusually, recording simultaneously into TS and OB receivers. The limiting factors in existing data are examined, the potential benefits of deeper receiver towing and denser OB acquisition assessed, and recommendations made for future 3D acquisition.Some well-established benefits of deep tow data are verified, such as the reduction in swell noise and decreased impact of the 0Hz ghost notch 1 . However, it is also shown that after careful denoise and deghosting, the shallow tow data is of similar quality. For OB data it is demonstrated that slow, aliased noise limits both data quality and useable bandwidth and that denser acquisition can successfully sample and remove this noise.Particularly, it is shown that survey design must not only provide sampling of primary signal, up to a desired frequency, but also provide at least one processing domain in which the slowest and most complex noise modes are un-aliased to the same frequency. This usually occurs naturally in towed streamer surveys which have densely sampled shot gathers, but is not always the case for OB surveys. Method -2D Field TrialsThe field trials were acquired by Caspian Geophysical using the M/V Gilavar. 4 tests were acquired, recording both TS and OB data simultaneously. The TS receiver spacing was 12.5m and the OB data receiver spacing was 75m, reducing to 150m on the flanks of the structure.A total of 33 processing flows were run by Schlumberger PetroTechnical Services in Gatwick, UK. These shared a core workflow and tested the effects of altering key parameters. This paper focuses on variations of acquisition shot density for the OB data and conventional vs broadband (de-ghosted)

Авторское право 2015 г., Общество инженеров нефтегазовой промышленности Этот доклад был подготовлен для презентации на Каспийской Технической конференции и выставке SPE, 4 -6 ноября, 2015, Баку, Азербайджан.Данный доклад был выбран для проведения презентации Программным комитетом SPE по результатам экспертизы информации, содержащейся в представленном авторами реферате. Экспертиза содержания доклада Обществом инженеров нефтегазовой промышленности не выполнялась, и внесение исправлений и изменений является обязанностью авторов. Материал в том виде, в котором он представлен, не обязательно отражает точку зрения SPE, его должностных лиц или участников. Электронное копирование, распространение или хранение любой части данного доклада без предварительного письменного согласия SPE запрещается. Разрешение на воспроизведение в печатном виде распространяется только на реферат объемом не более 300 слов; при этом копировать иллюстрации не разрешается. Реферат должен содержать явно выраженную ссылку на авторское право SPE.