385
DOI 10.1007/s12182-014-0352-3
Che Xiaohua
1, 2
, Qiao Wenxiao
1, 2
, Wang Ruijia
1, 2
and Zhao Yuhong
3
1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
2
Key Laboratory of Earth Prospecting and Information Technology, China University of Petroleum, Beijing 102249, China
3
China National Oil & Gas Exploration & Development Company, Beijing 100044, China
© China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2014
Abstract:
Transducers that are widely applied in cement bond evaluation tools, such as cement bond logs
and variable density logs, cannot radiate acoustic energy directionally because of the characteristics of
monopole sources. A phased arc array transmitter, which is a novel transducer that differs from monopole
and dipole transducers, is presented in this study. To simulate the acoustic eld generated by a phased
arc array in a uid-lled cased borehole with different channelings, a 3D nite-difference time-domain
method is adopted. The acoustic eld generated by a traditional monopole source is also simulated and
compared with the eld generated by the phased arc array transmitter. Numerical simulation results show
that the phased arc array radiates energy directionally in a narrow angular range in the borehole, thereby
compressing the acoustic energy into a narrow range in the casing pipe, the cement, and the formation. We
present the analyses of rst-arrival waveforms and the amplitudes of casing waves at different azimuthal
angles for the two different sources. The results indicate that employing a directional source facilitates
azimuthal identication and analysis of possible channeling behind the casing pipe.
Key words:
Phased arc array, azimuthal angle, rst-arrival amplitude, acoustic eld, cased borehole
Numerical simulation of an acoustic
eld generated by a phased arc array
in a uid-lled cased borehole
*Corresponding author. email: aclab@cup.edu.cn
Received August 21, 2013
2013b). However, azimuthal detection resolution for these
tools is limited by the radiation directivity of dipole sources.
As complex reservoirs are explored and developed, the need
for azimuthal acoustic logging becomes urgent (Li and Chu,
1997). For cased boreholes, detecting azimuthal direction for
channeling is crucial, but still faces difculties.
Traditional acoustic monopole sources are still extensively
used in traditional cement bond evaluation tools such as
cement bond log (CBL) and variable density log (VDL).
However, acoustic monopole sources cannot be employed
to evaluate the azimuthal direction of channeling, partial
channeling, and partial cement bonds. A segmented bond
tool (SBT) can identify channeling, as well as evaluate
channeling size and its azimuth. However, if SBT is used
alone downhole, only the bond condition of the rst interface
(i.e., the interface between the cased pipe and the cement) can
be assessed. To obtain the information on the second interface
(i.e., the interface between the cement and the formation),
SBT generally combined with CBL and VDL. Schlumberger
developed a new-generation tool called Isolation Scanner,
which evaluates strip channeling when cements with different
densities are bonded (Bellabarba et al, 2008). This tool is
a new well logging technology that combines ultrasonic
reflection, ultrasonic refraction, CBL, and VDL. Downhole
well logging tools with dipole sources are highly effective
Pet.Sci.(2014)11:385-390
1 Introduction
The acoustic properties of transducers determine the
functions and detection characteristics of acoustic well
logging tools, and essentially produce the new generation
of downhole tools (Qiao et al, 2011). Monopole transducers
were used in early acoustic well logging tools and are still
being used at present. The signicant radiation characteristic
of monopole transducers used in well logging tools is their
mono-directional horizontal directivity. Later on, multipole
sources have been studied and applied to geophysical
measurement practices (Chen and Tang, 2012; Kurkjian and
Chang, 1986; Kessler and Varsamis, 2001; Markova et al,
2010; Tang and Cheng, 2004; Tang, 2004; Tang et al, 2013a;
Wang et al, 2011; Wang et al, 2013). Combining a monopole
source with quadrupole and dipole sources in acoustic well
logging tools expands the functions and application scope
of this logging technology. Unlike a monopole source,
the directivity curve of a dipole source is
shaped, thus
extending acoustic tool functions. Dipole sources are used
in the new acoustic logging technology of remote acoustic
reection imaging (Tang and Wei, 2012a; 2012b; Tang et al,
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