A New Through-Casing Acoustic Logging Tool Using Dual-Source Transmitters
- Xiaoming Tang (School of Geoscience, China University of Petroleum (EAST)) | Yuanda Su (School of Geoscience, China University of Petroleum (EAST)) | Bo Zhang (Shuoren Times Technology)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
- 2 in the last 30 days
- 139 since 2007
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A new acoustic tool has been developed to measure formation acoustic properties through casing. This measurement is important for oil and gas production in mature field, and for wells that are cased without logging due to borehole stability issues. Conventional acoustic logging through casing in poorly bonded boreholes has been a difficult task due to the presence of overwhelming casing waves that mask the formation acoustic signal. To overcome the difficulty, we developed an acoustic tool using dual-source transmitters and the processing technique for the data acquired by the tool. This paper elaborates the operation principle of the new dual-source technology and demonstrates its application to cased-hole acoustic logging. By using the dual source design, the overwhelming casing waves from the poorly bonded casing are largely suppressed and the formation acoustic waves are significantly enhanced in the data acquisition process. Subsequent processing of the data reliably obtains acoustic velocity of the formation. The new tool has been tested in many cased wells with proven performance for various cement-bond conditions. The success of this technology makes cased-hole acoustic logging an effective operation that can be routinely used to obtain reliable formation information through casing.
Through-casing logging is an indispensable technology for exploration and production in brown field, considering the vast amount of cased wells around the world. The logging community has made breakthroughs in through-casing nuclear and resistivity measurements, but acoustic logging through casing remains a challenging issue for the industry. The issue is caused by the strong interference of casing waves in the casedhole logging data, especially when the casing and formation are poorly bonded (Tubman et al., 1986; Tang and Cheng, 2004; Tang and Patterson, 2005).
Signal processing techniques have been developed to suppress the casing waves and extract formation acoustic properties from the casedhole data (e.g., Valero et al. 2005, Tang and Patterson, 2005; Tang et al., 2014a). However, a condition for the signal processing is that the data should maintain certain signal-to-noise ratio for extracting the desired information from the data. This condition may not be satisfied in the presence of overwhelming casing waves of a poorly bonded borehole because, in the data digitization during logging, the gain for the digitizer is primarily controlled by the large-amplitude casing waves, rendering the small formation signal poorly digitized and the signal information inextricable. From the above root-cause problem analysis, one can see that the solution to the problem resides in suppressing the casing waves before the data digitization. The dual-transmitter acquisition technique is developed to achieve this goal.
|File Size||2 MB||Number of Pages||10|