1. CURRENT TRENDS IN ONSHORE SEISMIC DATA ACQUISITION: A
CASE STUDY ON CABLE-FREE NODAL SYSTEMS
Nabeel Yassi
Geokinetics (Australasia) Pty Ltd
601 Curtain Avenue East
Pinkenba Queensland 4008
Nabeel.Yassi@geokinetics.com
INTRODUCTION
The desire to conduct onshore seismic surveys without cables has been an elusive dream
since the dawn of seismic exploration. Since the late 1970s, seismic surveys were conducted
with cabled multi-channel acquisition systems. As the number of required channels steadily
grew, a fundamental restriction appeared with hundreds of kilometres of line cables deployed
on the ground. Seismic surveys within rugged terrain—across rivers, steep cliffs, urban areas,
culturally and environmentally sensitive zones—were both challenging and logistically
complex.
Modern technology has made different cable-free solutions practical for land seismic crews.
The main concern associated with cable-free nodal systems relates to whether the units are
working according to specifications during data acquisition. Quality controlled acquisition was
considered applicable to cabled systems only as data is monitored in real time. This
functionality is not readily available with nodal systems. Some nodal recording systems
claimed a level of two way communication for near real time quality control, however, the
applicability of these systems is yet to be the norm for standard surveys due to restrictions in
data transfer bandwidth and nodal battery life.
DATA QUALITY CONTROL
During the past five years more than twenty five 2D/3D nodal system seismic surveys were
conducted in Australia. The acquired seismic data met industry standards and proved the
equivalent to cable based data recordings, via the implementation of adaptable field quality
control practices during data acquisition:
 Up to three levels of instrument testing at the nodal field setup stage to ensure units
are operating within specifications prior to acquisition. Nodal instrument tests are
equivalent to cable instrument tests.

2.  Addition of real time quality control functionality through a third party hardware /
software such as SourceLink where source units can be monitored, with field
distortion monitored in real time.
 Deployment of extra nodes for quality control purposes. Additional nodes can be
deployed at the start of day, nodes can to be picked up at the end of day, data
harvested and field processed to ensure data integrity. Challenging zones can be
targeted for deploying the quality control nodes.
 Provision of weather stations around the seismic grid to monitor rain, wind speed,
etc. Tolerances are prepared beyond which acquisition can be postponed due to
weather generated noise.
 Adding a short segment of cabled system to monitor the noise level and complement
nodal recordings.
GEOPHONE ARRAY VERSUS POINT RECEIVER
The other concern associated with nodal recording is the traditional question of geophone
array versus point receiver data acquisition. For about two decades most of the geophysical
articles concerning land seismic acquisition made references to geophone array versus point
receivers. Land seismic sources typically generate energy that travels horizontally near
surface, also known as airwaves and ground-roll noise. Conventional geophone arrays were
used as a spatial anti-alias operator to attenuate seismic noise (Vermeer, 1990). Similarly,
geophone arrays suppress both correlated and uncorrelated ambient noise (Dean, et. al.,
2014). However, with the evolution of geophysical designs and the trend towards high channel
count nodal surveys, the geophone array is no longer to be considered as hardwire connected
geophone strings, but rather as a digital array that can be treated by sophisticated digital
processing.
Generally large receiver intervals and point receivers are sufficient to capture the necessary
wavelengths of deep reflection signals but the presence of noise necessitates much smaller
intervals. The more noise that is present in an area, the smaller should be the receiver interval.
To maintain an adequate design ratio of nodal counts to data quality; an optimum receiver
interval needs to be specified for a seismic survey.
Geophysical literature provides examples of the minimum receiver interval needed to record
unaliased seismic signals. Ait-Messaoud et. al. (2005) presented a high resolution, single
sensor case study with 2 metre receiver interval. For areas of poor data quality; Heath (2015)
suggested trace intervals of 5-10 metres for single sensor recording to provide a high spatial
sampling. On another survey, it was determined that a 12.5 metre receiver interval was
sufficient to record unaliased coherent noise generated by a complex near surface, with rapid
lateral velocity variations (Pecholcs, et.al., 2012). Prior to a regional 3D seismic acquisition in
Alaska, a comparison of nodal and cable systems showed the two were comparable (Yates
and Adiletta, 2013); however, the inherent reliability of the nodal system resulted in that system
being selected for the survey. In addition nodal data recorded at 25 m intervals was compared
with records at 50 m intervals. While the data quality of the 25 m interval data was better than
the 50 m interval data, it was not thought sufficient to justify a doubling of the receiver station
efforts.

3. GEOPHONE CONFIGURATION FIELD TESTS
To compare the performance of different geophone configurations on data quality, field tests
were conducted during the Bridgeport Energy Limited 2015 Playford East 3D seismic survey
in the Eromanga-Cooper Basin, South Australia. Table 1 lists the 3D survey recording
parameters. Tested geophone configurations included:
 G1 - ZLand GII nodes fully buried; the project’s normal production configuration
 G2 - ZLand GII nodes planted to base of node, only geophone spike buried
 G3 - ZLand nodes connected to a single external DT SOLO geophone
 G4 - ZLand nodes connected to external string of six SM-24 geophones, linear
array
 G5 - ZLand nodes connected to external string of six SM-24 geophones,
bunched array
Ten consecutive receiver stations for each of the sensor configuration types G2 to G5 were
deployed parallel to the normal production 3D receiver lines. The additional test receiver
stations were planted at a 1 metre offset to the north of the normal 3D receiver line. Production
receiver stations were considered as G1 for testing. To minimise the effects of surface
conditions on the tests results, the tested configurations were deployed at four different
locations within the 3D seismic grid.
Table 1: 2015 Playford Easy 3D seismic acquisition parameters
Design type Staggered orthogonal
Number of receiver lines in active patch 16
Number of receiver stations / receiver line in
patch
252
Live channels per patch 4,032 Channels
Recording System Fairfield ZLand G-II nodal system
Receiver station interval 20 m
Receiver line interval 320 m
Receiver line bearing 90.0˚
Seismic source array 2 x Input / Output Inc. AHV-IV (61,800 lb)
Vibroseis units
Source point interval 40 m
Source line interval 280 m
Source line bearing 0.0˚
Natural bin size 10 m x 20 m
Nominal fold 72
The acquired seismic test data was processed utilising a simple field data processing flow.
Identical processing was applied to each data set to analyse and evaluate the seismic signals
retained by each of the sensor configurations. Seismic datasets were analysed according to
four categories; receiver gathers, frequency spectrum on receiver gathers, 2D field mini-brute
stacks, and frequency analysis of mini-stacks.

4. RESULTS AND CONCLUSIONS
The test clearly confirmed the positive effects of burying the nodes. Receiver gather displays,
field brute stacks and amplitude/frequency spectrum (Fig. 1) clearly indicated that fully buried
nodes significantly improves the quality of the seismic data. Therefore planting the nodes with
the geophone spike only is not a worthy option.
Figure 1: G1 versus G2 mini-stacks spectrum
Completely buried nodes (left) versus nodes with spike only buried (right). Red seismic
signal - Black autocorrelated seismic noise component
The comparison between fully buried nodes and nodes connected to an external single
geophone with similar specifications shows that the seismic data of the two setups were very
similar. The external single geophone however, exhibits some additional seismic noise that
could be related to weather effects as a result of these geophones being planted to a shallower
depth. It could also be concluded that the additional area of the node’s physical dimensions
improves the node’s ground coupling characteristics.
The acquired data shows conventional geophone linear arrays managed to reduce the source
generated and ambient noise. However, the point receiver nodes show an equal data quality
level after a simple stacking process that eliminates the noise noticed at the high frequency
range; aliased frequency higher than the usable retainable frequency on the receiver gather
displays.
A simple stacking algorithm during field data processing successfully suppressed the seismic
noise that appeared on the raw receiver displays. The field processed mini-stacks show
seismic signal acquired by the conventional linear array and single point receivers are the
same along the survey targeted/usable frequency bandwidth (Fig. 2).

5. Figure 2: G1 versus G4 mini-stacks spectrum
Completely buried nodes (left) versus nodes connected to external string 6 geophones
normal array (right). Red seismic signal - Black autocorrelated seismic noise component
Seismic signals acquired by the fully buried nodes and the nodes connected to external strings
of 6 geophone elements grouped/bunched in a 1 metre diameter circle are almost identical on
the receiver gather displays, 2D mini-stacks and amplitude/frequency spectrum.
Based on the test results, it is practical to conclude that the conventional geophone array
reduced seismic noise; however, the point receiver nodes at 20 metres station interval
provided equal seismic signal with a simple stacking algorithm. The additional benefits
associated with the use of a nodal system supersedes the conventional geophone array
benefits, particularly when the end seismic products are comparable through standard seismic
data processing.
ACKNOWLEDGMENTS
The author is grateful to Geokinetics for authorisation to publish this paper and Bridgeport
Energy Limited for permission to publish some of the seismic records from the 2015 Playford
East 3D seismic survey.
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