LF Land Seismic Acquisition: What, How, and Why
Mahrooqi, Said *1; Rawahi, Salim 1; Yarubi, Saeed 1; Hunt, Keith 1; Yahyai, Awad 1; Abi, Said 1; Baeten, Guido 2
(1) Exploration, Petroleum Development Oman (PDO), Muscat, Oman. (2) Shell Global Solution, Shell, Rijswijk, Netherlands.
The emission and recording of low frequency land seismic data is recognised as beneficial for deep target imaging. Petroleum Development Oman along with their seismic contractors are currently working towards continuous, reliable acquisition of full bandwidth land vibrator surveys, utilising sweeps with a starting frequency as low as 1.5 Hz.
There are several recognised or perceived limitations to this mode of operation, including
●Limited data on enduring test of ’conventional’ vibrators
Phase and distortion control
●Use of conventional (10Hz) geophones
It is fair to say the longer term potentially detrimental effect on using standard vibrators as low frequency source has not yet been quantified.
In order to assist in the design and acquisition of high quality land seismic surveys from 1.5Hz, PDO and its contractors with assistance from Shell have carried out a number of source tests. These include varying the sweep bandwidth, sweep length, sweep linearity and vibrator drive level. The vibrator used for these tests was the ION 362 type (65,000 lbs). All tests were performed keeping in mind, quality and productivity requirements.
The results that will be presented in this paper will show that vibrators are able to generate low frequencies with no observed mechanical damage. Our tests have also shown that despite an increase in the sweep length and with standard slip time, productivity can be maintained, without the introduction of further harmonics.
In March 2011, PDO commenced acquiring seismic data using a non-linear custom 9 sec sweep, with a 7 sec slip time over a bandwidth of 1.5 - 86 Hz. This low frequency seismic data provides greater potential for imaging the deep target, and for enhancing the potential of applications such as Full Waveform Inversion.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain