AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Seismic Source Parameters Optimization in Shallow Water Area Offshore Abu Dhabi, U.A.E
(1) ADMA-OPCO, Abu Dhabi, United Arab Emirates.
(2) WesternGeco, Abu Dhabi, United Arab Emirates.
Seismic source parameters are one of the important specifications for a seismic survey. Conventional thinking is that larger sources produce higher energy, and thereby improve data quality.
In shallow water areas offshore Abu Dhabi, U.A.E, OBC seismic survey is commonly acquired with air-gun array as the primary seismic source. However, the source size is limited due to operational constraints such as shallow water depth and scattered production facilities. Although several seismic surveys have been acquired in the region, the impact of source size on data quality is still open for discussion. In this regards, a 2D-2C OBC pilot seismic survey was acquired in a shallow water area in the region.
In this seismic survey, several datasets were acquired with different source parameters, however using the same source vessel and air-gun array. The number of air-guns, total volume of air-guns in the array and shot-point interval (SPI) were varied among these datasets, while the same pressure, depth and synchronization of air-guns were maintained.
During the processing, the same parameters and velocity were applied to all datasets to minimize any differences due to processing effects. Data quality for each dataset was evaluated at various processing stages. At pre- and post- noise attenuation stages, hydrophone, geophone and summed data were each analyzed to evaluate the amplitude levels of both signal and noise, the signal-to-noise ratio (S/N) and the signal frequency bandwidth (SFB). The same analysis was also performed on the final summed data at the final stage after signal processing, migration imaging and stack.
The main findings are: (1) higher source energy improves S/N of acquired data, however the improvement in S/N against source energy is a little; (2) even the smallest source acquires data quality over the required S/N and SFB at the target two-way time window; (3) deeper two-way time window causes lower S/N and SFB, and the effect is larger on SFB; (4) shorter SPI leads to higher S/N of acquired data; and (5) processing itself greatly improves data quality in all cases of source parameters.
Consequently, shorter SPI and appropriate processing could compensate for a lack of source energy, then even a small source could achieve the required data quality with the aid of suitable SPI and processing. The results will encourage to investigate even smaller sources which are easier for the operations and friendlier to the environment.