Chengdu · China Real-time QC in HCHP seismic acquisition Ning Hongxiao, Wei Guowei and Wang Qiucheng, BGP, CNPC

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Summary High channel count and high productivity bring huge challenges to the QC activities in the high-density and high-productivity seismic acquisition because the traditional ways, such as manual QC with the help of printed monitor records, cannot meet the requirements of real-time QC. Therefore, BGP researched and developed some special real-time QC techniques, including fast data transmission, backup and dump, vibroseis real-time QC, remote real-time QC and so on. In the field, the techniques provided the comprehensive real-time QC to the high productivity acquisition and achieved very good result, which shows that the real-time QC technology developed by BGP will have bright applying prospect in the high productivity seismic acquisition projects in the future. 1 Introduction With the increasing of the recording capacity of the seismic instrument, the high productivity acquisition technology is becoming more and more mature. The present seismic acquisition is developing toward the trend of massive data and high productivity. Number of Recording channels for each shot reaches to tens of thousands, daily production exceeds ten thousands of shots, and therefore the daily volume of data may be several TB. Because of the massive data, the QC using traditional methods, such as manual checking the field data, cannot keep up with the field recording progress and fail to meet the requirements of the high productivity acquisition. This requires complete change of the existing quality control technology. For the real-time QC of the acquisition projects with

high productivity and massive data, three questions need to be solved . The first one is the I/O of massive data. The huge data volume brings big challenge to data I/O. Fast and stable data transmission, reading and writing have become the premise to do the real-time QC. The second is how to do the QC rapidly. For the high productivity acquisition, the key is to complete the QC within very short time. The last is the change of the QC objects. With the development of the high productivity acquisition technology, the QC objects have been changed from the single shot to the status of the recording equipment, acquisition parameters and so on. According to the features of the high productivity acquisition, the problems of data transmission, writing and reading have been successfully solved by using optical fiber data transmission and the optimization of hardware and software. Through the application of parallel technology and algorithm optimization, BGP forms a set of special QC techniques, and has implemented the fast real-time QC to vibrators, acquisition parameters, active spread, seismic data, etc. The fast real-time QC technology has achieved very good result in the practical application in the field. 2 Real-time QC technology The real-time QC of high productivity acquisition should satisfy two requirements. One is real time. The QC must be completed within very short time, judging whether a shot is bad or not and reminding the observer to reshoot the bad shot if need. The application result shows that BGP’s real-time QC to two shots with fifty thousand receivers per shot can be completed in three seconds, which can

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completely meet the current requirements of the high productivity acquisition. The other is having the comprehensive and effective QC functions. BGP developed KL-RtQC system, which includes not only onsite real-time QC of seismic data properties, the vibrator status, acquisition parameters and the active spread, but also the remote QC. In the practical application of the QC system, most of the bad shots can be found, which provides effective guarantee to the smooth production. 2.1 Stable data transmission technology For the high productivity seismic acquisition, the shooting speed is very high and received data volume per shot is usually very large. Quick access to raw data, the stability of data transmission and no interference to the recording system are very important. If not handled properly, it will cause the recorder crash, data transmission congestion or other problems, which will affect the acquisition efficiency severely. First, hardware problem need to be solved. If gigabit network cards are used, maximum data transfer rate is 80 MB/S, but average data transfer rate is only about 50 MB/S. In a 3D project in Oman, the data volume of single shot was 350MB, and the shooting speed was 2 shots every 7 seconds. So the minimum transmission rate should be more than 100MB/s. Only optical fiber transmission can solve the data transmission problem. Using optical fiber to connect the recording server and the RtQC workstation provided a transmission rate of 200MB/s when doing data transmission test. The actual transmission rate in the production was 130MB/s because of lower I/O speed of the hard disk, but it met the demand of the high productivity acquisition project.

2.2 Vibroseis real-time QC Considering environmental protection and high efficiency demand, vibrators have been widely used in the high productivity acquisition in the world, so the QC of vibrator working status is very important. The QC mainly includes vibrator performance monitoring, COG check, T-D rule QC and so on. In addition to the monitoring of sweep check sum, vibrator performance monitoring includes six indexes: average phase, peak phase, average distortion, peak distortion, average force and peak force. Comparing the actual value and the standard value, an alert will be given when the error exceeds the standard requirements. COG check is mainly to get coordinate error of the center of the vibrator array, and then give an alert if the error exceeds the standard requirements. T-D rule QC is typically for the project using dynamic sweep technology. Dynamic sweep is the combination of flip-flop, slip sweep, and DSSS sweep. During production, every sweep is checked whether it follows the time-distance rule. If not, an alert will be given to the observer. As shown in figure 1, the numbers in the first row is the vibrator number and each following row indicates one of the properties. Each cell has 5 bars representing the nearest 5 sweeps. Once a sweep exceeds the standard, the initial green color will be replaced by yellow. At the same time, a warning message will be shown in the message window below displaying the details about the alert.

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Figure 1 Vibroseis real-time QC

2.3 Acquisition parameter QC Normally the acquisition parameters for each project are fixed once the parameters are determined. Some parameters including recording parameters are rarely set by mistake. However, some unexpected errors may happen when changing survey lines or restarting the recorder. In this case, very serious quality incident might happen because it’s difficult to find. Through checking the head block information of raw shots, we can immediately find the mismatch and avoid the incident. The monitored acquisition parameters includes the sample rate, record length, pre-gain, filter type, SEGD version, processing type, sweep length, etc. 2.4 Data quality real-time QC Energy, frequency (dominant frequency, band width), S/N and ambient noise are the four properties to evaluate the data quality. In order to monitor these

properties, a selected shot is regarded as standard shot, and the average value of each property of the shot as the standard value. For a new shot, each property can be compared with the standard value. If the difference exceeds the set criteria, the shot will be treated as abnormal shot. The QC flow is shown in figure 2. In the field, these properties may change a lot because of the complex surface condition or the utilization of multiple types of sources in one project. As a result, it will affect the evaluation result. In order to eliminate the influence of terrain factor on the evaluation result, a work area will be divided into different zones according to the terrain. Each shot is only compared with the standard shot in the same zone. Similarly, a shot is only compared with the standard shot with the same type of shooting source. To increase the QC accuracy of the above four properties, 3 different time-windows can be selected in different areas, such as the area before first break

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(FB), the FB area and hyperbola area (figure 3), to calculate property value respectively and evaluate the data quality. The value in the window before FB can be used for ambient noise QC and S/N QC, in FB window for the energy QC and in hyperbola window for the energy, frequency or S/N QC.

The property value of standard shot

comparing

Evaluation result

The property value of current shot

The evaluation of standard shot

……

……

……

…………

Figure 2: The evaluation flow chart t

Figure 3 Time window for real-time QC

(Red for pre-FB window, green for FB window, blue for hyperbola window)

2.5 Spread real-time QC The QC of field spread is to find out problematic traces, including the abnormal traces and noise traces. The number of abnormal traces, an important field QC indicator, directly determines the quality of acquired seismic data. So the information about the abnormal traces should be timely informed to the observer for the rectification. As an index of the noise level of a shot, the number of the noise traces may directly indicate the range of the noise influence on the spread. Monitoring the noise traces enables us to learn about the distribution of the noise sources. Combining the ambient noise QC, we can avoid judging the shots with very few recording traces affected by the strong noise as noise shots. Abnormal traces include great value trace, missing trace, misconnecting trace, strong amplitude trace and weak amplitude trace. Noise traces include single frequency interference trace and low S/N trace disturbed by other noise. The abnormal traces and noise traces are mainly identified through comparing and analyzing the sampling value of each trace within the specified time window. Valuating the QC result, the real-time QC system will give an alert once the percentage of abnormal traces and noise traces exceeds the set criteria. 2.6 Remote real-time QC Remote real-time QC is a very important QC means. It can realize real-time QC of the field acquisition in the office, quickly help to solve technical issues in the field, and provide the online training or guidance.

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To achieve the remote QC, the main problem to be solved is the data transmission. Cable or WIFI network can be used for the short distance data transmission, and mobile network may be used for the long distance data transmission. Because the bandwidth of the mobile network is small, data thinning and compression should be first carried out to ensure smooth real-time monitoring. As shown in figure 4, the 428 server transfers the seismic data to the RtQC workstation through the local network, and then the data is transferred to the GSM Android phones, IPADs or computers via 3G, 4G, or WIFI network. Figure 5 shows the interface of the RtQC system and remote real-time QC office

Figure 4 Remote RtQC (Left: 428 server and RtQC workstation, right:

IPAD, GSM phone and computer)

Figure 5 Remote QC

(Left: Remote QC office, Right: RtQC system interface)

2.7 Statistical analysis technology For all the QC attributes, statistical analysis of the areal distribution can be conducted using the real

time QC system. Figure 6 shows the energy distribution of raw shots for a 3D project. The color of each dot on the map represents its energy level. Blue means weak energy and red strong energy. As we can see, the energy turns stronger from east to west in the block.

Figure 6 Energy distribution map

Figure 7 Noise distribution map

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Figure 7 is Noise distribution map. The color of each dot represents the noise level, blue color means weak noise and red color strong noise. From the map we can see, the noise level is zonal distribution.

3 Application Based on all the above mentioned real-time QC technology, BGP developed a real-time QC software system, KL-RtQC. The KL-RtQC system has been applied in many high productivity acquisition projects in China, Saudi Arabia, Oman, and other countries. From 2015 to now, this system has been applied in 80 projects in China and 22 projects in other countries, and achieved very good results. Case 1: Project A in China This is a vibroseis project, using G3i as recorder with 16200 live channels and 220MB data per shot. The average daily production is 2000 VPs and the highest daily production is 3111 VPs. The KL- RtQC system completes real-time QC of 124000 VPs. Applying result shows that the consistent rate is 92.2% comparing with manual QC, and 100% of the sever incidents is identified (Table 1).

Table 1 KL-RtQC application result in the 3D project

Total of checked shots 124000

Abnormal VPs found manually 2525

Warned VPs found by RtQC 2717

Abnormal VPs found by RtQC 2353

Abnormal VPs not found by RtQC 172

Successful identification rate 92.2%

Sever incidents identified 100%

Figure 8 shows the automatic identification of a weak energy shot in the project. In the figure, the bar relative to energy property is yellow, which means this shot has weak energy.

Figure 8 Weak energy shot automatic identification

In the field acquisition, the monitoring of missing traces is one important item of the spread QC. Figure 9 is a successful example of identifying the missing traces using the KL-RtQC system in the project. In the figure, the bars relative to the properties of missing traces and abnormal traces are yellow, which means this shot has missing traces.

Figure 9 Missing traces automatic identification

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Case 2: Project B in the Middle East Natural earthquake could be encountered occasionally during the field acquisition. As an interference with strong energy, natural earthquake always presents certain directivity and relatively low frequency. It can be easily identified through monitoring the range of dominant frequency and the noise. In figure 10, the bar of dominant frequency in the real-time QC window is yellow, which means it is an abnormal shot caused by an earthquake.

Figure 10 Earthquake Automatic identification

4 Conclusions To achieve fast and effective real time QC of high productivity seismic acquisition, BGP researched above seven real time QC techniques and developed the software system KL-RtQC, which has been widely applied in the productivity acquisition projects. Summarizing all the application results, the following conclusions can be drawn:

1) The seven real-time QC techniques implement comprehensive monitoring of vibrator performance, acquisition parameters and seismic data quality, and can automatically identify the abnormal shots. 2) The high efficiency real-time QC technology can meet the real-time QC requirements of all present high productivity acquisitions. 3) Applied in the high productivity seismic acquisition projects, the KL-RtQC system can ensure the smooth operation of the projects, and greatly improve the production efficiency. References Shao Yumei, Wang Xiuhuai, a new method of automatic eliminating the noise in seismic data, OGP，1991，30（3）：98-106