Experimental studies for monitoring water‐level by dipole‐antenna array radar fixed in the subsurface

Ebihara, Satoshi; Nagoya, Kaoru; Abe, Noriyasu; Toida, Masaru

doi:10.3997/1873-0604.2005035

Cited by 13 publications

(5 citation statements)

References 22 publications

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“…Pioneering borehole radar tools fixed in the subsurface have been proposed for monitoring the movement of the water level at considerable depths (Ebihara et al, 2006;Sato and Takayama, 2007), and EM logging tools have already proved the GPR potential in imaging the neighborhood of a well (Liu et al, 2004;Mason et al, 2008). We believe our study can stimulate research in order to allow an innovative and promising application for GPR technology.…”

Section: Introductionmentioning

confidence: 73%

Coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications

et al. 2011

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The recent introduction of smart well technology allows for new geophysical monitoring opportunities. Smart wells, which allow zonal production control, combined with monitoring techniques capable of capturing the arrival of undesired fluids, have the potential to significantly increase the oil recovery. We consider borehole radar as a valuable technology for monitoring of the near-well region. By coupling a drainage process of a bottom water-drive reservoir with electromagnetic simulations, we find that radar sensors located in the production well can successfully map the fluid saturation evolution. In low-conductivity reservoirs r < 0:02 S=m ð Þ , a system performance above 80 dB is necessary to record reflections in the range of 10 m.Higher conductivity values strongly reduce the radar investigation depth. Despite the technical challenges to implement a permanent down-hole radar system, the potential semi-continuous acquisition would make 4D groundpenetrating radar a promising technology in capturing the near-well fluid dynamics. Suitable environments are bottom water-drive reservoirs with thin oil layer and heavy oil reservoirs exploited by steam-assisted gravity drainage processes.

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Section: Introductionmentioning

confidence: 73%

Coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications

et al. 2011

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“…First, a small loop array antenna was adopted (Sato and Tanimoto ; Ebihara, Sato and Niitsuma ). This was followed by the introduction of a dipole array antenna, whose elements were fed by an optical modulator system (Ebihara ; Ebihara et al ; Sato and Takayama ; Takayama and Sato ), or coaxial cables (Ebihara et al ). The latter system has been used for 3D imaging of a fault (Ebihara, Kawai and Wada ), and researchers succeeded in reducing the bore size of the antenna through the addition of ferrite cores (Ebihara et al ).…”

Section: Introductionmentioning

confidence: 99%

Probe rotation effects on direction of arrival estimation in array‐type directional borehole radar

Ebihara

Wada

Karasawa

et al. 2017

Near Surface Geophysics

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This paper discusses the relationship between feeding line delay compensation and direction of arrival estimation in an array-type directional borehole radar. In this radar, since the space available for an array antenna is limited by the borehole diameter, direction of arrival estimation is based on small travel time differences among array elements, and an accurate compensation of feeding line delays is important. Computer simulation confirmed that the radar probe rotation in a borehole leads to errors in the direction of arrival estimation of greater than 15° if the delays associated with the feeding array antenna elements are not compensated to within 0.1 ns. This may be caused by a failure to measure the time delays of electrical circuits around the feeding points of the antenna elements. In this case, we suggest that the lengths of system components other than the coaxial cables should be kept to less than 3 cm. Based on these investigations, we developed an array-type directional borehole radar for a geotechnical project to locate foundation piles. In a field experiment, we confirmed that direction of arrival estimation errors were below about 15°, although the radar probe rotated through more than 180° during the measurement, thanks to correct compensation of the cables. With the correct compensation, we demonstrated three-dimensional location of a buried cylindrical conducting object, which was located at 2 m from the radar in wet soil. We were able to estimate the reflection point position with an accuracy of 34 cm, which is the averaged error of the three-dimensional location, while allowing the radar probe to rotate. tool used in such projects (Daniels 2004). Soundings made with GPR have provided valuable information on objects buried in the subsoil up to several metres below the ground surface. Due to the sounding depth limitation of GPR, borehole radar has started to be utilised at construction sites. Borehole radar is a type of GPR (Slob, Sato and Olhoeft 2010) in which frequencies between 20 MHz and 100 MHz are used for long-range detection. Most conventional borehole radar systems for single borehole application use two vertical dipole antennae, which are omnidirectional. This type of radar has been applied to the detection of buried foundation piles (Yamashita and Toshioka 2002), and it is useful in two-dimensional space measurement for the determination of the depth and the radial distance (range) of targets parallel to the measurement borehole. However, to detect and range objects such as foundation piles in three-dimensional (3D) space using a single borehole, a directional borehole radar system is needed. As a directive antenna for the directional borehole radar, a cavity-backed antenna has been used; this system mechanically rotates the antenna inside the borehole

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“…Another approach for a directive antenna is to arrange small dipole antenna elements in a circle within a borehole (Ebihara ; Ebihara et al . ; Sato and Takayama ; Behaimanot et al . ).…”

Section: Introductionmentioning

confidence: 99%

Estimating the 3D position and inclination of a planar interface with a directional borehole radar

Ebihara

Kawai

Wada³

2012

Near Surface Geophysics

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In this paper, we present a signal processing method suitable for estimating the position of a planar interface and its inclination using a directional borehole radar. The receiving directive antenna in a radar system is a coaxial‐fed circular dipole array antenna in a borehole (CFCAB), which we have proposed previously. The method combines least‐square fitting with a model of plane‐wave incidence and uses an inverse boundary scattering transform. This approach makes it possible to estimate parameters from measurements collected at only two narrowly separated depths of a radar sonde. We give a numerical example to verify the proposed method. In this simulation, the array data were generated with the Method of Moments modified for a borehole radar. We conducted field experiments in the Nakatatsu mine in Japan, where there is a fault in the skarn. We constructed a 3D image of the fault with a directional borehole radar and the signal processing method. The image agrees well with the information obtained from boring core samples and observations in the gallery.

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Experimental studies for monitoring water‐level by dipole‐antenna array radar fixed in the subsurface

Cited by 13 publications

References 22 publications

Coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications

Coupling ground penetrating radar and fluid flow modeling for oilfield monitoring applications

Probe rotation effects on direction of arrival estimation in array‐type directional borehole radar

Estimating the 3D position and inclination of a planar interface with a directional borehole radar

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