Application of Hydrocarbon Detection Technology in the Thin Sand
Reservoirs
Chunlei Li
1,*
, Ruisong Zhang
2
, Wei Ding
1
, Wenqi Zhang
1
, Xiaoling Zhang
1
and Xiaoyan Liu
1
1
CNPC Research Institute of Petroleum Exploration & Development (RIPED), China;
2
CNPCHK (Thailand) Limited/Sino-U.S. Petroleum Inc.
Keywords
: Thin sand layer, hydrocarbon detection, instantaneous spectral analysis, attenuation gradient
Abstract:
In response to the complex geologic conditions, such as many broken fault blocks, small scale of reservoirs,
and big lateral and vertical variations of reservoirs in the research area, the drilling success ratio in the
margin of the oil area has been increased and the traditional deployment idea of development wells have
been upgraded into the new idea aimed at thin sand bodies by using of the hydrocarbon detection
technology based on the integrated achievements of geology, sedimentary and reservoir. The hydrocarbon
detection technology has obtained remarkable effects and effectively increased drilling success ratio in the
development process of the research area.
1 THEORETICAL BASIS OF
PREDICTION OF RESERVOIRS
BEARING HYDROCARBON
According to the seismic exploration principle based
on the reflected wave method, the seismic signals
are gradually attenuated in their propagation process
in subsurface. There are many factors affecting the
attenuation of seismic signals, mainly including the
interface between adjacent lithofacies, the reflection
mechanism in faults and fractures, spherical
spreading in the homogeneous medium, and
variation of physical properties in the homogeneous
medium (including oil, gas, water, etc.) (Batzle et
al., 1997). Among these attenuation factors, that we
most care about is the last one, i.e. seismic
attenuation caused by the variation of physical
properties in the homogeneous medium (Figure 1).
The instantaneous spectral analysis technology
provides us with a means for the analysis of seismic
wave attenuation attributes in frequency domain. In
general, the energy attenuation of seismic signals is
increased in the high frequency part under the same
geologic conditions due to the existence of oil and
gas. In comparison with the frequency features
without attenuation, the whole frequency band after
attenuation will shrink towards the low frequency
part. Energy attenuation is often indicated by the
several physical methods such as the energy
attenuation gradient with frequency, low frequency
energy, the frequency corresponding with the
specified energy ratio, the energy ratio in the
specified frequency band, etc. Different physical
methods reflect the possibility of existence of oil
and gas from different aspects (Batzle et al., 1992).
Attenuation gradient is one of attenuation
attributes. As shown by the red arrow in Figure (2),
attenuation gradient reflects the variation of seismic
energy in the high frequency part with frequency,
and can indicate the attenuation velocity during
propagation of seismic waves. The attenuation
gradient value (ATN_GRT) of seismic waves
increases in the presence of the attenuation caused
by such as oil and gas etc. in addition to the
diffusion effect during seismic wave propagation in
a single-phase media and the reflection mechanism
of seismic waves at the reflection interface in multi-
phase media (Li et al., 2014).
Low frequency energy is another important
attenuation property and it indicates the intensity of
low frequency energy (Sinha et al., 2005). Due to
the existence of oil and gas, the energy attenuation
in the high frequency part of seismic waves is larger
than in the low frequency part, and the whole
frequency range will shrink to the low frequency
360
Li, C., Zhang, R., Ding, W., Zhang, W., Zhang, X. and Liu, X.
Application of Hydrocarbon Detection Technology in the Thin Sand Reservoirs.
In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 360-363
ISBN: 978-989-758-342-1
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

range after attenuation, causing the energy of low
frequency part to be enhanced (Figure 3).
Figure 1: Principle of fluid detection with the attenuation
gradient.
Figure 2: I Schematic of frequency attenuation gradient.
The third geophysical attribute that indicates
hydrocarbon attenuation is the frequency
corresponding with the specified energy ratio
(Figure 4). The total energy is 1 in the effective
frequency range. If the energy in the low frequency
range specified is 85%, the frequency corresponding
with 85% of the energy can be searched from the
starting frequency in the effective frequency range,
which is called F1. If the energy in the low
frequency range specified is 65%, the frequency
searched is called F2. The frequency corresponding
with the specified energy ratio will decrease if there
are oil and gas etc. Based on the same principle, the
frequency corresponding with the maximum energy
can be searched in the whole effective frequency
range, i.e. initial attenuation frequency. The smaller
the initial attenuation frequency, the greater the
probability of oil and gas existing.
Figure 3: Schematic of low frequency energy.
Figure 4: Schematic of the frequency corresponding with
the specified energy ratio.
Another geophysical attribute that indicates
hydrocarbon attenuation is the energy ratio
corresponding with the specified frequency (Figure
5). In case of specifying a frequency F in the
effective frequency range, the energy within the
range from the initial frequency to the frequency F
can be calculated, which is called the energy of the
low frequency range (E
low
). The percent of E
low
to
the total energy of the whole frequency range (E
full
)
is called the energy ratio corresponding with the
specified frequency. If there exist oil and gas etc.,
the energy of the high frequency range will
decrease, thus causing the energy ratio from energy
corresponding with the specified frequency in the
low frequency range to the total energy to be
E
f
ΔE
Δf
ΔE
ATN_G RT= ——
Δf
E
85%
E
f
F F
1
F
2
E
65%
1
Application of Hydrocarbon Detection Technology in the Thin Sand Reservoirs
361

increased (Wang, 2007). That is, if the energy ratio
corresponding with the specified frequency
increases, the possibility of existence of oil and gas
is large, and can be determined according to the
variation of the energy ratio corresponding with the
specified frequency.
Figure 5: Schematic of the energy ratio corresponding
with the specified frequenc
y
(Wan
g
et al., 2012).
Oil and gas reservoirs show typical character of
two-phase media. According to studies, when oil
and gas existing, the seismogram show more
obvious kinetics features such as “low frequency
resonance, high frequency attenuation”. Therefore,
the above various frequency properties can be used
as the basis for judging the reservoirs bearing
hydrocarbon ( Wu and Liu, 2010).
2 APPLICATION EXAMPLE
ANALYSIS (TAKING BY
BLOCK IN THAILAND AS AN
EXAMPLE)
According to the response analysis of attributes in
wells, the reservoirs of Lancrabu Formation respond
to frequency attenuation gradient and the energy
attributes of the low frequency part (Figures 6 and
7), indicating high low-frequency energy and high
attenuation gradient. However, the attributes
prediction result completely comes from seismic
information, so it is restricted largely by the quality
of seismic data and has certain multiplicity.
Frequency attenuation gradient and low-
frequency energy are sensitive to the reservoirs
bearing hydrocarbon and have some certain
correlation with the initial production of wells.
According to the comparison result, the frequency
attenuation gradient match well with the initial
production of wells in the study area, and it can be
used as the prediction basis for hydrocarbon
detection. Figures 8 and 9 are the distribution map
of hydrocarbon detection of K and L sand layers in
Lancrabu Formation in the study area. According to
the hydrocarbon detection result, the dominant area
predicted bearing hydrocarbon is located mainly in
the central part of the study area (indicated with red
circle). Anomalies are weakened in the east and west
part, the scope of anomalies is small in the south,
there is no indication of hydrocarbon bearing in the
north, and the indication bearing hydrocarbon of K
sand layer is more obvious than L sand layer.
Figure 6: Diagram of well BY1-side seismic attributes.
Figure 7: Diagram of well BM1-side seismic attributes.
Energy of low
fre
q
uent
y
Attenuation
gradient
Attenuation
gradient
Energy of low
frequency
IWEG 2018 - International Workshop on Environment and Geoscience
362

Figure 8: Map of hydrocarbon detection of K sand
layer in Lancrabu Formation.
Figure 9: Map of hydrocarbon detection of L sand
layer in Lancrabu Formation.
3 CONCLUSIONS
The research area in Thailand has complex geologic
conditions, broken fault blocks, thin oil reservoirs,
poor physical properties of reservoir, and complex
and diverse controlling factors of reservoirs. After
more than 20 years of development, the remaining
oil and gas distribution is very complex, it is more
and more difficult to tap the potential, and the
development conflicts have become increasingly
prominent. With the hydrocarbon detection
technology, the distribution of the remaining oil and
gas can be depicted accurately and drilling risks can
be reduced greatly. According to the effect of
application of the research area in Thailand, this
method can be used to effectively predict the
distribution of remaining oil and gas and especially
has achieved a good effect in the prediction of thin
reservoirs of complex fault blocks. However, the
attribute prediction result completely comes from
seismic data, so it is also mainly restricted by the
quality of seismic data and multiplicity. Therefore,
multiple factors shall be considered
comprehensively such as structure, sedimentation,
reservoir, reservoir forming, etc. in well
deployment.
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