Introduction &Summary
Fifteen hundred square kilometers of the 3D OBC Seismic Survey was acquired, over an 18-month period in 2000 and 2001, as a joint Venture between ADNOC, ADMA-OPCO and ZADCO. The seismic acquisition contractor was Petroleum Geo-Services (PGS).
This paper concentrates on some of the Operational, Quality &HSE aspects and the many challenges faced in acquiring such a highly specified orthogonal OBC survey (in excess of 300 fold) over a very active field which is extremely densely populated with infrastructure and partly located over very shallow water.
The field has hundreds of well head towers (jackets), huge super complexes, satellite platforms and many hundreds of kilometers of criss-crossing, untrenched oil, gas and water pipe-lines. Areas of dense coral pinnacles and other field debris exist. Water depths less than 5m were measured but even these depths were effectively reduced in many areas by the presence of the hazards.
Compound the above with super complexes up to several hundred meters long, construction vessels &barges, stimulation vessels, supply vessels, diving vessels, other survey vessels, shuttle vessels, production activities, hundreds of mooring buoys, a field operated by multi ethnic/linguistic workforce and dual Oil Company Operatorship.
Throw in a seismic crew consisting up to 9 vessels, 150 crew, 120 kilometres of OBC cables and the ingredients are complete for what must be one of the most complex and intensive OBC seismic surveys ever to be acquired anywhere in the world!
The immense Operational, HSE and Quality challenges of the survey were overcome by an incredible level of Joint Venturer team work, excellent communications, extensive risk assessment, operational safety audit, innovation, peer assist and, not least, having a world class seismic acquisition contractor.
Basic Acquisition Parameters and Statistics
The seismic survey commenced in August 2000 and completed mid-January 2002 at an average daily production rate of just under 3 square kilometers per day. A total of 1505 square kilometres of full fold data was acquired using an orthogonal technique (source lines perpendicular to receiver lines as opposed to parallel in the ‘swath’ technique) to yield a wide azimuth data set fit not only for structural interpretation but also for advanced reservoir characterization purposes. The exceptionally high fold (by comparison to other typical OBC surveys) was obtained through 100m and 300m source and receiver line spacing respectively, 6 active OBC receiver lines, an in-line and cross-line maximum offset of 3600m (yielding a ‘diagonal’ maximum offset of 5100m). For spares and repair inventory purposes up to 120kilometres of cable were available. A working (at sea) spread of 6 receiver lines of 14.4 km each (total 86.4km) was typical although more active cables were utilized during the shallow water portion of the survey due to restricted access for the dynamically positioned recording vessels. The receiver cables were rolled in-line as opposed to cross-line, the latter of which has tended to be more typical of OBC surveys. The receiver station interval was 50m with an, effectively, point array.
