TY - JOUR
AU - Wu,, Jinping
AB - Abstract An azimuthally sensitive acoustic bond tool (AABT) uses a phased arc array transmitter that can provide directionally focused radiation. The acoustic sonde consists of a phased arc array transmitter and two monopole receivers, the spaces from the transmitter being 0.91 m and 1.52 m, respectively. The transmitter includes eight transducer sub-units. By controlling the high-voltage firing signal phase for each transmitter, the radiation energy of the phased arc array transducer can be focused in a single direction. Compared with conventional monopole and dipole transmitters, the new transmitter provides cement quality evaluation with azimuthal sensitivity, which is not possible with conventional cement bond log/variable density log tools. Laboratory measurements indicate that the directivity curves for the phased arc array and those computed theoretically are consistent and show good agreement. We acquire measurements from a laboratory cistern and from the field to validate the reliability and applicability of the AABT. Results indicate that the AABT accurately evaluates the azimuthal cement quality of case-cement interfaces by imaging the amplitude of the first-arrival wave. This tool visualizes the size, position and orientation of channeling and holes. In the case of good case-cement bonding, the AABT also evaluates the azimuthal cementing quality of the cement formation interface by imaging the amplitude of formation waves. acoustic logging, azimuth, phased-arc array, cementing quality, test, electronic system 1. Introduction Cementing is a key technique in exploring and exploiting oil and gas. This technique effectively isolates oil, water and gas layers, and holds the casing in place. Cementing quality evaluation determines the cementation of the cement ring and is mainly based on detecting the interfaces between the casing and the cement ring (the first interface) and between the cement ring and the formation (the second interface). Acoustic logging tools provides an effective means to detect and evaluate cementing quality. The cement bond log (CBL) and the variable density log (VDL) are representative conventional tools of this kind. CBL tools generally employ a single transmitter and a single receiver mandrel structure. They emit high-voltage acoustic pulses with an approximate frequency of 20 kHz, and measure the casing wave traveling through the casing to evaluate the first interface (Pardue et al 1963; Xue et al 2000; Wang et al 2011). Combined CBL/VDL tools have a mandrel structure consisting of a single transmitter and a pair of double receivers to evaluate the first and second interfaces. The spaces between the transmitter and the double receivers are 0.91 m and 1.52 m, respectively. The near receiver checks the primary wave amplitude of the refracted compressional wave traveling along the casing, whereas the far receiver measures the amplitude of casing and other follow-up waves. However, neither CBL nor VDL tools can easily determine the azimuth of cement trenches because of the lack of azimuthal resolution (Bolshakov et al 2010; Qiao et al 2011). Recent advances in acoustic logging technology have enabled rapid improvements in cement quality evaluation. New logging tools developed by several international corporations have emerged successively, such as the segmented bond tool (SBT) from Baker Hughes and the isolation scanner (IBC) from Schlumberger (Bigelow et al 1990; Van Kuijk et al 2005; Bellabarba et al 2008; Tang et al 2012; Loizzo et al 2013). Compared with traditional CBL/VDL tools, these new tools have azimuth resolution. The SBT conducts measurement using six SBT pads with twelve high-frequency directional transducers fixed on them. The SBT can also determine the cementing quality and the related circumferential orientation of the first interface simultaneously. However, this tool does not address the second interface (Bigelow et al 1990). The IBC combines classic pulse-echo technology with the ultrasonic technique of flexural wave imaging, then characterizes the annular environment and evaluates different types of cement, combining independent measurements (Van Kuijk et al 2005; Bellabarba et al 2008; Tang et al 2012). However, several limitations exist in practical application because the pad-type structure and complex devices of mechanical rotation and orientation are used for circumferential measurement. These features easily wear the SBT or IBC, with a high cost and high requirement for the well condition in high-frequency measuring mode (Tang et al 2012). Addressing these limitations, Qiao et al (2003, 2005, 2009) conducted numerous innovative works on the acoustic logging sonde and proposed the use of phased arc array transducers with 3 D radiation characteristics. These acoustic phased arc array transducers transmit and receive acoustic signals in random 3 D space directions. Math models and experiments have demonstrated that the main wave angle becomes narrow and the sound power becomes great when phased arc array transducers are used as transmitters; thus, real acoustic azimuth logging is achieved (Qiao et al 2008; Che et al 2010; Wu et al 2013). Furthermore, these transducers can be used in anisotropic formation evaluation, reflection wave imaging for wave-impedance discontinuities, and petroleum engineering applications, such as directional drilling and cross-hole exploration (Qiao et al 2008; Lu et al 2011; Wang 2012). The methods define a new-generation azimuthally acoustic bond tool (AABT) where acoustic phased arc array transducers are used to detect cementing quality. This tool not only solves the problem of the lack of azimuth resolution for traditional CBL/VDL tools but also works reliably and is realized easily without the complex structure of mechanical rotation. 2. The phased arc array and its operational principle The dimension of an acoustic transducer is smaller than that of a wavelength. As a preliminary numerical model, we can assume that each array element of the phased arc array is approximately a point sound source (Chen 2006; Qiao et al 2008; Wang 2012). The sketch is shown in figure 1. Nmax point sources are evenly arranged on the circumference of radius a. This circumference is located in the xoy plane. When the sound ray is transmitted from the arbitrary direction (α,θ) ⁠, the sound path difference of the array element i relative to the reference point O is ξi≈r¯i⋅e¯=xi⋅ex+yi⋅ey+ziez.1 Figure 1. Open in new tabDownload slide The phased arc array coordinate diagram. (a) The phased arc array coordinate diagram with evenly distributed point sources. (b) The 3D coordinate system. Figure 1. Open in new tabDownload slide The phased arc array coordinate diagram. (a) The phased arc array coordinate diagram with evenly distributed point sources. (b) The 3D coordinate system. When the sound ray from the principal maximum direction is transmitted, the sound path difference of the array element i relative to the reference point O is ξ0i≈r¯i⋅m¯=xi⋅mx+yi⋅my+zimz.2 Therefore, the phase difference of the array element i between the sound rays from the arbitrary direction (α,θ) and the principal maximum direction (α0,θ0) is Δφi=ωca[ cosαi(sinθcosα-sinθ0cosα0)             +sinαi(sinθsinα-sinθ0sinα0)]         =ka[sinθcos(α-αi)-sinθ0cos(α0-αi)].3 where αi is the angle between the radius vector of the array element i and the positive x -axis in the x–y plane, αi=i2π/Nand c is the velocity of sound. The wave number is k=ω/cand a is the radius of the phased arc array. According to the principle of superposition, the directivity function of the phased arc array of point sources can be expressed as D(a,θ,a0,θ0,ω)=|∑i=1NAie-jΔφi∑i=1NAi|.4 Figure 2 shows the structure of the phased arc array and the operational schematic diagram that is actually used in the AABT. Eight elements are evenly placed along the circumference. Each element is composed of two polarized piezoelectric ceramics and an unpolarized ceramic sheet which are fused together. Each array element functions independently, and is electrically and acoustically isolated. When an electric field excitation is applied to the array element, one of the piezoelectric ceramics stretches, whereas the other shortens at the same time, and thus, the entire composite ceramic vibrates. When the phased arc array of the eight elements is in operation, the three adjacent array elements are excited by high-voltage pulses with phase delay. Consequently, sound waves can be radiated in the direction of one orientation. For example, consider three elements, A8, A1 and A2. A1 is the center of the three elements, and A8 and A2 are excited first. A1 is excited by an excitation signal with some delay time. An equivalent linear-phased array with three array elements is then formed. If the wave fronts of A2 and A8 propagate to the straight line of oo′ at time τ1 (i.e., we mark the moment for time 0), then the center element of A1 is excited after a moment of τ1 ⁠. As a result, the wave fronts of the three array elements are simultaneously tangent to line oo′ at the moment of τ1 ⁠. A2, A3 and so on are selected as the center in turn. The three adjacent array elements work at different times. Radiation beams can be formed separately on different circumference orientations, which can achieve a circumferential scanning measurement. Figure 2. Open in new tabDownload slide The phased arc array structure and the operation schematic diagram. Figure 2. Open in new tabDownload slide The phased arc array structure and the operation schematic diagram. Numerical simulation and experimental results show that the energy distribution of the tube waves, which is excited by the phased arc array, is uneven in the circumferential direction, and that the energy of the tube waves is strongest in the acoustic axis of the transducer. Therefore, the acoustic bond logging tool that includes the phased arc array achieves cementing quality evaluation with azimuthal resolution (Qiao et al 2003; Lu et al 2011). 3. Tool structure Figure 3 illustrates the principle behind the AABT, which consists of the acoustic sonde and the electronic system. The acoustic sonde in turn consists of the acoustic phased arc array transmitter and two monopole receivers with a frequency of approximately 15 kHz. One of the receivers has 0.91 m spacing and the other has 1.52 m spacing. figure 4 shows a photo of the tool. The acoustic phased arc array transmitter includes eight transducer units and radiates acoustic signals at random directions of the circumference by employing radiation control technology for the phased array. The key components of the electronic system are system control and transmitter electronics (Lu et al 2011). To be compatible with conventional CBL/VDL tools, the AABT employs 0.91 m and 1.52 m spacing, and thus, consistent results are achieved compared with CBL/VDL tools with the same parameters. In one work period, the acoustic phased arc array transmitter emits eight acoustic signals with an interval of 45° and each monopole receiver obtains eight signals from different directions. Therefore, a total of 16 acoustic signals can be achieved from the 0.91 m and 1.52 m receivers in one work period. Figure 3. Open in new tabDownload slide Overall structure of the AABT. Figure 3. Open in new tabDownload slide Overall structure of the AABT. Figure 4. Open in new tabDownload slide Photo of the AABT. Figure 4. Open in new tabDownload slide Photo of the AABT. In accordance with CBL/VDL tools, the AABT mainly measures the longitudinal symmetric mode L(0,2), which travels along the direction of the borehole axis in the casing (Rose 2004). The mode wave, described as the casing wave in this paper, is a type of casing wave that travels with a velocity close to the body wave velocity of the casing material when its frequencies vary within the range of the acoustic logging. Acoustic imaging for the amplitude and attenuation of the primary wave of the casing wave, as well as the amplitude of the formation wave, is obtained to evaluate the circumferential cementing quality of the first and second interfaces. When differences in circumferential cementing quality or defects exist in a certain direction, the amplitudes of eight casing waves received from different directions vary greatly and can be used to evaluate the circumferential cementing quality of the first interface and the casing damage. The energy of the formation wave excited by the phased arc array transmitter is also distributed unevenly along the circumference. When the first interface has good cementing quality, the circumferential cementing quality of the second interface is evaluated based on the differences existing in the circumferential amplitudes of the formation waves. 4. Electronic systems The electronic system of the downhole AABT mainly consists of acoustic-phased excitation, receiving, data acquisition, system control and telemetry interface circuits. The excitation electronics are located at the lowest end of the tool, and the main component is the acoustic-phased excitation circuit. The system control electronics are located at the upper end of the tool, and the main structure includes the receiving, data acquisition, system control and telemetry interface circuits. The telemetry interface circuit is compatible with the Eilog imaging logging system of the China National Petroleum Corporation. The communication rate of this system reaches up to 430 kbps in a 7000 m armored logging cable. The telemetry interface is connected to the system to download commands and upload waveform data in real time (Lu et al 2011). The system control circuit is used to control each function module, to set working parameters and to generate an operation time sequence by a tool control bus (TCB). The TCB is connected to all the functional modules of the tool. The functional circuit units that receive commands from the TCB include the receiving, data acquisition and excitation circuits. The TCB goes throughout the entire instrument in the mechanical structure, passing through the acoustic excitation transducer that requires multi-channel high-voltage pulses in particular. Thus, the anti-interference design of the bus is important. A serial mode is adopted in the TCB, and the TCB consists of clock and data lines. The TCB reception is achieved by a complex programmable logic device (CPLD) in each functional circuit unit. The command bits are received via counting and decoding, and can set the function circuit units synchronously or separately. The reception control is flexible. To improve the electromagnetic compatibility of the system, electromagnetic shielding is applied to the cables of the TCB in the tool system, thus ensuring reliable operation of the TCB. The inner structure of the downhole tool is limited by circuit layout and wiring such that the system control, telemetry interface and data acquisition circuits are located in different circuit modules. Large quantities of waveform data in the data acquisition module must first be transmitted to the system control circuit to be filtered and cached. Then, the downhole telemetry system transmits the data to the surface system. A reasonable design is required for the connection between the data acquisition and system control modules to minimize wiring between boards and to ensure the electromagnetic compatibility of the system. Therefore, we adopt serial data transmission as the high-speed local bus (HLB). The HLB consists of clock, data and selection lines, and its transmission rate is 5 Mbps. The one-way operation between multi-source and single goals is realized. All devices share clock and data lines, but the selection lines of the source are independent. The control logic of the HLB is achieved by the CPLD. First-in first-out (FIFO) memory is adopted as the data cache of the source and the target. Working parameters, such as data quantity, were established by the digital signal processor (DSP) in the system control module. The target devices drive the clock, whereas the source devices send data synchronously by the clock. All transmission controls are completed by the CPLD after the DSP starts data transfer operations. No intervention occurs from the DSP during transmission, and the DSP processes the data received in this period. 4.1. Excitation circuit of the phased arc array The phased arc array transmitter consists of eight units. By controlling the high-voltage fire signal phasing of each transmitter, the radiation energy of the phased arc array transducer is transmitted in a single direction. The work mode of the phased control indicates that the width and phase of the radiation pulses are controlled by the system control circuit. This feature requires a flexible excitation control circuit, and the CPLD satisfies this requirement. The pulse signal source consists of the command decoder, excitation logic controller, driver circuit, high-power excitation circuit, high-voltage pulse transformers, energy storage circuit, power supply, and so on. A schematic diagram of the source is shown in figure 5. Figure 5. Open in new tabDownload slide Schematic diagram of the phased excitation source. Figure 5. Open in new tabDownload slide Schematic diagram of the phased excitation source. The command decoder and the excitation controller are obtained by the CPLD, and their structure is shown in figure 6. The main component units are the decoding state machine, flip-latch of parameters, excitation element selection, excitation delay control, excitation pulse width control and the excitation control logic of each array unit. The delay parameters, the excitation pulse width and the selection of working array units are set by the system control circuit. The state machine and decoder decode these parameters and latch various working parameters. The logic circuits, such as excitation element selection, excitation delay control and excitation pulse width control, handle the received excitation parameters and produce the control signals of each array unit. When the excitation start command is received, the selected array units synchronously work in accordance with the phased method.The driver circuit converts the transistor–transistor logic signal exported by the CPLD into the 12 V complementary metal oxide semiconductor logic signal to increase the response speed of the complementary driver circuit. Each channel of the complementary driver circuit consists of two complementary middle power vertical metal oxide semiconductor tubes. The circuit provides large current drive signals for the high-power devices in the excitation circuit to turn pulse drive tubes on and off rapidly. Figure 6. Open in new tabDownload slide Schematic diagram of the logic controller for phased excitation. Figure 6. Open in new tabDownload slide Schematic diagram of the logic controller for phased excitation. 4.2. System control and telemetry interface circuits Overall coordination control of the tool is undertaken by the system control circuit. The controller area network (CAN) peripheral device integrated into the DSP of the system control circuit is used as the interface that connects with the downhole telemetry section. figure 7 shows the principle diagram of the system control and telemetry interface circuits, which are composed of a TMS320LF2407A DSP, CAN driver, FIFO storage, random access memory (RAM), a high-speed data receiver controller and the interface control logic of the peripheral devices. After the telemetry interface circuit receives various commands from the surface, the system control circuit decodes the commands and saves the result to local registers. Driven by depth interruption, the circuit sends related commands to start a new cycle of data collection and sets the working timing and parameters for the receiving channels, acquisition circuit and excitation circuit. Once data acquisition is finished, the DSP starts its reading function to read the result from the data acquisition circuit through the HLB. To improve the signal-to-noise ratio (SNR), the received acoustic signals are oversampled by the acquisition circuit. We filter and extract the data from the HLB and save the data in the RAM. When the data upload commands are received from the telemetry interface, the circuit delivers the processed data to the CAN interface module and uploads the data to the surface. Figure 7. Open in new tabDownload slide Schematic diagram of the system control and telemetry interface circuits. Figure 7. Open in new tabDownload slide Schematic diagram of the system control and telemetry interface circuits. 4.3. Data acquisition circuit Figure 8 shows a schematic diagram of the two-channel synchronous data acquisition circuit. This circuit mainly consists of a wide-band operational amplifier with a high-performance, analog-to-digital converter (ADC) AD7899SR-1, FIFO memory, acquisition controller and high-speed serial data transmission interface. Each channel has its own independent ADC acquisition circuit, which is controlled by the CPLD. The CPLD decodes the command from the system control circuit, controls the two-channel acquisition to operate synchronously and generates the write–control signal of FIFO memory. The system control circuit sends acquisition and control commands to the acquisition controller by the TCB, reads the acquired data via the HLB and processes these data. Figure 8. Open in new tabDownload slide Schematic diagram of the data acquisition circuit. Figure 8. Open in new tabDownload slide Schematic diagram of the data acquisition circuit. 4.4. Receiving circuit The receiving circuit receives analog signals from the transducers, processes these signals and outputs signals with a suitable dynamic range to the data acquisition circuit. A schematic diagram of this circuit is shown in figure 9. The received signal consists of useful and undesirable signals, with the latter having amplitudes that are significantly higher than those of useful signals. Consequently, useful signals with high quality cannot be obtained without filtering, and the process can be affected significantly. Interference signals include multiple frequency components, such as high-frequency interference signals and 50 Hz power signals. The frequency range of the received acoustic signals from the transducers is often from 5 kHz to 20 kHz. Hence, the frequency range of the band-pass filter is from 5 kHz to 20 kHz. Various geological structures are responsible for different amplitudes of the received acoustic signals, and the received signal voltage from the transducer may range from a few microvolts to a few millivolts. To adapt the amplitude range of acoustic signals, the receiving circuit should have a large dynamic gain controller. The adjustable range of gain is from 0 dB to 60 dB, with a stepping of 6 dB, which is realized by a programmable amplifier. The CPLD completes the interface with the TCB, decodes the received commands and generates the channel control signals. Figure 9. Open in new tabDownload slide Schematic diagram of the receiving circuit. Figure 9. Open in new tabDownload slide Schematic diagram of the receiving circuit. 5. Experiments and analysis 5.1. Directivity test of the phased arc array The actual performance of the transmitter transducer is affected by several factors, including mechanical structure, installation and the acoustic window of the tool shell. An acoustic test is required to verify the radiation characteristics of the phased arc array installed in the tool.An important method to evaluate the radiation characteristics of the phased arc array is to investigate the horizontal directivity. This measurement requires satisfaction of the far-field boundary condition and accurate control of the location, movement speed and distance (Wu et al 2013). The experimental installation based on the positioning control system is installed in a quasi-anechoic tank measuring 5 × 5×4 m. A photo of the test tank is shown in figure 10. A schematic diagram of the experimental apparatus is shown in figure 11. The positioning system has four motion directions; namely, X, Y, Z and C. The motion track of the positioning system is controlled by the stepping motor. The maximum position space in the X, Y and Z directions is 3920, 3930 and 3455 mm, respectively. To ensure safety of motion, the system is controlled by limit switches in the X, Y and Z directions at both ends of the rail. The operation status of the limit switches is controlled by the host program. The C axis revolves at any rotation angle and is not restricted by the switch control. The return difference of the X, Y and Z axes is controlled within 1 mm, and is able to fully satisfy measurement requirements. The working head of the positioning system is provided with a clamping device into which the hydrophone, transmitter transducer and experimental probe are installed, and accurately moves anywhere in the tank. Figure 10. Open in new tabDownload slide Photo of the quasi-anechoic test tank. Figure 10. Open in new tabDownload slide Photo of the quasi-anechoic test tank. Figure 11. Open in new tabDownload slide Schematic diagram of the experimental apparatus for the phased arc array. Figure 11. Open in new tabDownload slide Schematic diagram of the experimental apparatus for the phased arc array. The positioning control system connects with the host computer through Ethernet, thus allowing control of the motion of the positioning system. A high-voltage excitation source generates excitation signals for the phased arc array. This excitation source is controlled by the host computer through Ethernet. Based on the user settings, the host computer downloads the working parameters through the serial interface. Meanwhile, the high-voltage excitation source outputs the synchronization signals to the acquisition system. After processing by the program controlled gain amplifier with low noise and large dynamic range, the acoustic signals received by the receiving hydrophone are inputted to the acquisition system. The acquisition system connects to the host computer through a network interface. The acquired data are uploaded to the host computer, and the preamplifier gain control and data acquisition parameters are downloaded by the network interface. Figure 12 shows the comparison of the horizontal directivities between the theoretical calculation and the experimental results of one sub-array installed in the tool. The results indicate that the agreement between the theoretical calculation and the experimental measurement is good. According to the analysis of the waveform obtained from the hydrophone, the main frequency of the waveform is approximately 15 kHz. The experimental measurement and theoretical calculation results prove that the phased arc array of the acoustic logging tool has good focusing properties within the frequency range. Hence, the phased arc array has good azimuthal resolution characteristics. The main frequency of the waveforms, i.e., the resonant frequency of the transducers, satisfies the operational frequency of the acoustic logging tool. Figure 12. Open in new tabDownload slide Comparison of the horizontal directivities of one sub-array from the theoretical calculation and the experimental measurement. Figure 12. Open in new tabDownload slide Comparison of the horizontal directivities of one sub-array from the theoretical calculation and the experimental measurement. Next, we test the horizontal directivities when the sub-array of the phased arc array is operating with and without phase-controlled excitation. figure 13 shows the test results. The main angle of the radiation beam is obviously small when the sub-array is excited with phase-delay signals. By contrast, the angle is large when the sub-array is excited with signals of the same phase. Therefore, the main angle of the radiation beam is controlled by phase delay, and azimuthal resolution and SNR are improved by using the phased arc array. Figure 13. Open in new tabDownload slide Experimental comparison of the horizontal directivities of the phased arc array with and without phase-controlled excitation. Figure 13. Open in new tabDownload slide Experimental comparison of the horizontal directivities of the phased arc array with and without phase-controlled excitation. The consistency of the horizontal directivities of the eight sub-arrays significantly influences the measurement results. Thus, we test the consistency of these sub-arrays, and the results are shown in figure 14. For comparison, each circumferential directivity is rotated to place its main sound beam along the 0°  direction. In the figure, Sub_x is the directivity curve when the sub-array, where element x is the center, is excited by the phase-delay signals. For example, Sub_1 implies the directivity curve when the sub-array consisting of Elements 8, 1 and 2 is operated. As shown in the graph, when the eight sub-arrays are operated individually, the main angles of the radiation beams are along the 0° or 360°  direction. The radiation beams are symmetrical around the center line of the main angle. The angles of 3 dB are all approximately 45°  and are consistent. The acoustic energy is weak and several small side lobes exist in other directions. In conclusion, the consistency of the horizontal directivities of the eight sub-arrays is good and satisfies the requirements of the azimuthal cementing quality evaluation. Figure 14. Open in new tabDownload slide Experimental comparison of the horizontal directivities of eight sub-arrays with phase-controlled excitation. Figure 14. Open in new tabDownload slide Experimental comparison of the horizontal directivities of eight sub-arrays with phase-controlled excitation. 5.2. Tests in a cylindrical lab cistern Acoustic logging tools are often tested in cylindrical lab cisterns, which are also used to verify the directivity and reliability of the AABT. The cistern we used in the present experiment is made of aluminum tubing with a gap on the top side with an angle of 135.5° . The AABT is placed in the center of the tube, which is full of water, to simulate the logging environment being filled with liquid. figures 15(a and d) show the schematic sections of the cistern, the AABT and the phased arc array transmitter. When the sub-array of the phased arc array faces the gap on the pipe, excitation and propagation of the casing wave are negatively affected, and the first wave amplitude is small. However, when the sub-array deviates from the gap on the pipe, the first wave amplitude is large. Figure 15. Open in new tabDownload slide The experimental results of the cylindrical lab cistern test. (a) The schematic sections of the cistern, the AABT and the phased arc array transmitter when Element 1 is facing the gap. (b) The waveforms of the 0.91 m receiver when Element 1 is facing the gap. (c) The waveforms of the 1.52 m receiver when Element 1 is facing the gap. (d) The schematic sections of the cistern, the AABT and the phased arc array transmitter when Element 2 is facing the gap. (e) The waveforms of the 0.91 m receiver when Element 2 is facing the gap. (f) The waveforms of the 1.52 m receiver when Element 2 is facing the gap. Figure 15. Open in new tabDownload slide The experimental results of the cylindrical lab cistern test. (a) The schematic sections of the cistern, the AABT and the phased arc array transmitter when Element 1 is facing the gap. (b) The waveforms of the 0.91 m receiver when Element 1 is facing the gap. (c) The waveforms of the 1.52 m receiver when Element 1 is facing the gap. (d) The schematic sections of the cistern, the AABT and the phased arc array transmitter when Element 2 is facing the gap. (e) The waveforms of the 0.91 m receiver when Element 2 is facing the gap. (f) The waveforms of the 1.52 m receiver when Element 2 is facing the gap. Figures 15(b and c) show the waveforms of the 0.91 m and 1.52 m receivers when Element 1 is facing the gap. We use the number of the middle element in the sub-array to mark the waveform. The number 1 waveform in the figure refers to the waveform received by the transducer when the sub-array consisting of Elements 8, 1 and 2 is excited. figures 15(b and c) show that when Element 1 is facing the gap, the first wave amplitude of the casing wave, which is excited by the sub-array consisting of Elements 8, 1 and 2, is the lowest. The first wave amplitudes of the casing wave excited by different sub-arrays have a regular variation; i.e., when the difference between the acoustic axis of the sub-array and the gap of the tube is large, the first wave amplitude is also large, and vice versa. figures 15(e and f) show the waveforms when Element 2 is facing the gap. The wave amplitude excited by the sub-array consisting of Elements 1, 2 and 3 is the smallest, and the rule of the first wave amplitudes is consistent with that in figures 15(b and c). We also test the tool when the other elements face the gap and obtain the same conclusions. The experimental results are consistent with the theoretical analysis, thus demonstrating the azimuthal detection capability of the AABT. 5.3. Analyses of the field testing results The dominant frequency of the acoustic signal inspired by the transmitting transducer of the AABT is approximately 15 kHz. Theoretical and experimental studies have certified that within this frequency range, the casing and formation waves along the axial direction of the well are inspired. According to the feature of wave amplitudes in the circumference, the circumferential cement bond qualities of the first and second interfaces are evaluated.Figure 16 shows the evaluation results of the cementing quality in one well. The first trace in the figure is the GR curve; the third and fourth traces are the amplitude images of the first waves and the travel time imaging of the 0.91 m spacing waves in the circumferential directions from 0° to 360° ; the fifth trace is the minimum, maximum and average wave amplitudes of the first wave; the sixth trace is the minimum, maximum and average travel times of the first wave; and the seventh, eighth and ninth traces are the waves of 0.91 m spacing, the variable density curves of 0.91 m spacing, and the variable density curves of 1.52 m spacing, respectively. The cementing quality shown in the imaging map is in accordance with that in the variable density map. The well segment with existing cement channeling is reflected clearly in the imaging map and its circumferential character is also shown. Simultaneously, the results shown in the imaging map and the variable density curve have good correspondence with the maximum, minimum and average primary wave amplitudes and reaching times. For example, in the 1802 m well segment, cement channeling and its position in the circumferential direction is clearly shown in the imaging map and in the variable density curve. The maximum and minimum amplitudes of the first wave also exhibit obvious differences, thus demonstrating the circumferential cementing quality of the aforementioned well segment. Figure 16. Open in new tabDownload slide Evaluation results of the cementing quality in one well. Figure 16. Open in new tabDownload slide Evaluation results of the cementing quality in one well. Figure 17 shows the measurement results of the AABT in one well in the north of China. The traces from left to right show the GR curve; depth curve; formation wave amplitude curve; formation wave amplitude imaging; first wave amplitude imaging; maximum, minimum and average amplitude curves of the formation wave; and the waves received by the 1.52 m spacing receiver and their variable densities. When the cementing quality of the first interface is poor, the wave amplitude of the formation is less than that of the casing wave and cannot be picked up accurately, such as at the depths of X797 to X799 m and X812 to X813 m. The variation of the circumferential formation wave imaging is in accordance with that of the first wave amplitude imaging, thus confirming that the imaging of the formation wave amplitude reflects the character of the casing wave because the casing wave amplitude is significantly large. In this case, the imaging of the formation wave in the circumferential direction cannot be used to explain the cementing quality of the second interface. When the cementing quality of the first interface is moderate, the casing wave has almost no influence on the extraction of the formation wave amplitude. The variations in the amplitude imaging of the formation wave and the amplitude imaging of the first wave are contradictory, such as at the depth of X815 to X818 m. When the cementing quality of the first interface is good, the casing wave is nearly unobservable in the waveforms. The character of the formation wave amplitude in the circumferential direction responds to the cementing quality of the second interface, such as at the depth of X801 m to X808 m. The casing wave amplitude is minimal and even in the circumferential direction, whereas the formation wave amplitude is large and also even in the circumferential direction, thus illustrating that the bond quality of the first and second interfaces is good. For the depth of X808 to X812 m, the casing wave amplitude is minimal and even in the circumferential direction, whereas the formation wave amplitude is minimal and uneven in the circumferential direction, thus illustrating that the bond quality of the first interface is good and that cement channeling or aperture is present in the second interface. According to the minimum value of the formation wave amplitude in the figure, the location of cement channeling or aperture is 0° and 180° , respectively. Figure 17. Open in new tabDownload slide The measurement results of the AABT in one well in the north of China. Figure 17. Open in new tabDownload slide The measurement results of the AABT in one well in the north of China. 6. Conclusions Based on acoustic phased array technology, an AABT with a main frequency of 15 kHz was developed. The tool uses a phased arc array transmitter and does not employ a complex mechanical rotating structure. The main wave angle becomes narrow and the sound power becomes large through the electronic control system, and a true circumferential scanning measure is realized. Measurements conducted in a laboratory half-space cistern show that the tool accurately detects the loss of the casing pipe and its orientation, as well as verifies circumferential azimuth detection performance. The field results prove that the AABT exhibits good circumferential azimuth detection performance and evaluates the bond quality of the two interfaces. The actual measured azimuth resolution is higher than 40°, which better satisfies on-site operational requirements to evaluate the orientation characteristics of cementing quality. In addition to evaluating cementing quality for oil exploration, the developed tool also has potential applications in gas storage evaluation, non-homogeneous formation evaluation, oriented perforation, oriented drilling and other processes in petroleum engineering. Acknowledgements This study is supported by the National Science Foundation of China (61102102, 11134011, 11204380 and 11374371), Major National Science and Technology Projects (2011ZX05020-002), the Science and Technology Project of CNPC (2011 A-3903, 2011B-4001) and the Foundation of China University of Petroleum (KYJJ2012-05-07). The authors would like to thank Prof. Honglin Zhao at China University of Petroleum, Beijing, for his help in the design of the tool structure. References Bellabarba M , Bute-Loyer H , Froelich B , Roy-Delage S L , Kuijk R , Zeroung S , Guillot D , Moroni N , Pastor S , Zanchi A . , 2008 Ensuring zonal isolation beyond the life of the well , Oilfield Rev. spring (pg. 18 - 31 ) OpenURL Placeholder Text WorldCat Bigelow E L , Domangue E J , Lester R A . , 1990 A new and innovative technology for cement evaluation 65th Annual Technical Conf. and Exhibition New Orleans SPE Bolshakov A , Dubinsky V , Tang X M , Patterson D J , Donskoy D , Barolak J G . , 2010 , Casing resonant radial flexural modes in cement bond evaluation (U. S. Patent 7,681,450) Che X H , Qiao W X , Ju X D . , 2010 Characteristics of acoustic field generated by acoustic phased arc array transmitter in the borehole formation , Acta Petrolei Sinica , vol. 31 (pg. 343 - 346 ) OpenURL Placeholder Text WorldCat Chen X L . , 2006 , Basic methodological investigation on three dimensional acoustic logging around the borehole Shandong Ph.D. dissertation China University of Petroleum Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Rose J L . , 2004 , Ultrasonic waves in solid media Cambridge Cambridge University Press Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Loizzo M , Miersemann U , Lamy P , Garnier A . , 2013 Advanced cement integrity evaluation of an old well in the Rousse field , Energy Procedia , vol. 37 (pg. 5710 - 5721 ) 10.1016/j.egypro.2013.06.493 Google Scholar Crossref Search ADS WorldCat Crossref Lu J Q , Ju X D , Qiao W X , Che X H , Deng L , Wu W H . , 2011 Electronic system design of azimuthally acoustic bond tool , Well Logging Technol. , vol. 35 (pg. 284 - 287 ) OpenURL Placeholder Text WorldCat Pardue G H , Morris R L , Gollwitzer L H , Moran J H . , 1963 Cement bond log-a study of cement and casing variables , J. Petroleum Technol. , vol. 15 (pg. 545 - 555 ) Google Scholar Crossref Search ADS WorldCat Qiao W X , Ju X D , Che X H . , 2009 A kind of acoustic logging with phased arc array transducer , Well Logging Technology , vol. 33 (pg. 22 - 25 ) OpenURL Placeholder Text WorldCat Qiao W X , Ju X D , Che X H , Lu J Q . , 2011 Progress in acoustic well logging technology , Well Logging Technology , vol. 35 (pg. 14 - 19 ) OpenURL Placeholder Text WorldCat Qiao W X , Ju X D , Chen X L . , 2005 , A downhole acoustic transmitter with controlled arbitrary directivity (China Patent 200310115236. 1) Qiao W X , Ju X D , Chen X L , Li G , Hu T T . , 2003 , Downhole acoustic arc array transmitter with controlled azimuthal directivity (China Patent 03137596. 0) Qiao W X , Che X H , Ju X D , Chen X L . , 2008 Acoustic logging phased arc array and its radiation directivity , Chinese J. Geophys. , vol. 51 (pg. 939 - 946 ) OpenURL Placeholder Text WorldCat Tang H P , Zhang H T , Li G R , Niu L L , Zhao H H , Zhang Y J . , 2012 Applications of isolation scanner (IBC) imaging logging in horizontal well , J. Oil and Gas Technol. , vol. 34 (pg. 88 - 93 ) OpenURL Placeholder Text WorldCat Van Kuijk R , Zeroug S , Froehlich B , Allouche M , Bose S , Miller D , le Calvez J L , Schoepf V , Pagnin A . , 2005 A novel ultrasonic cased-hole imager for enhanced cement evaluation Int. Petroleum Technology Conf. Doha IPTC Wang M Y , Liu J S , Lu X M , Wang Q H . , 2011 Contrastive analysis between MAK&SGDT and SBB cementation quality evaluation , Well Logging Technology , vol. 35 (pg. 176 - 179 ) OpenURL Placeholder Text WorldCat Wang R J . , 2012 , Simulation research on acoustic logging in fluid-filled borehole surrounded by anisotropic formations Beijing Ph.D. dissertation China University of Petroleum Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC Wu J P , Qiao W X , Che X H , Ju X D , Lu J Q , Wu W H . , 2013 Experimental study on the radiation characteristics of downhole acoustic phased combined arc array transmitter , Geophysics , vol. 78 (pg. D1 - D9 ) 10.1190/geo2012-0114.1 Google Scholar Crossref Search ADS WorldCat Crossref Xue M , Chu Z H , Li Y H , Jiang H , Zhao B C , Chen X D . , 2000 Discussion on several problems in the estimation of cement bond quality , Well Logging Technology , vol. 24 (pg. 470 - 475 )470–75 OpenURL Placeholder Text WorldCat © 2014 Sinopec Geophysical Research Institute
TI - Azimuthally acoustic logging tool to evaluate cementing quality
JO - Journal of Geophysics and Engineering
DO - 10.1088/1742-2132/11/4/045006
DA - 2014-08-01
UR - https://www.deepdyve.com/lp/oxford-university-press/azimuthally-acoustic-logging-tool-to-evaluate-cementing-quality-telt13at7C
VL - 11
IS - 4
DP - DeepDyve
ER -