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H istory of W ire l ine S onic L og g ing


In a patent awarded in 1935 , Conrad Schlumberger specified how a transmitter and two receivers might be used to measure the speed of sound in a short interval of rock penetrated by a borehole (right).1 He claimed that the speed and attenuation of sound would characterize lithology. His invention failed because neither logging engineers nor the technology of the time was able to detect the short time difference— tens of microseconds (µ s)— between signals traveling at the speed of sound to receivers separated by just inches. During World War II, the necessary electronics emerged, making sonic logging possible.2 According to one account, the first oilfield application of sonic logging was for casing-collar location, in 1946.3 Most other historical accounts state that the first sonic applications appeared after the 1948 experiments by Humble Oil Research, followed by Magnolia Petroleum Company and Shell.4 These companies designed devices to collect sonic-velocity information for time- depth conversion of surface seismic sections and for correlating seismic reflections to lithologic interfaces. The tools featured one transmitter and one or two receivers separated from the transmitter by isolating material. By the mid-195 0s, service companies and oil companies were acquiring sonic- logging data to generate synthetic seismograms for comparison with surface seismic sections.5 In 195 7, having licensed the Humble patent, Schlumberger introduced its first sonic tool, the velocity logging tool (VLT), for improving seismic interpretation.


The early Magnolia Petroleum paper had


hinted at the additional possibility of using sonic velocities to determine porosity and lithology, but it was scientists in the research division of Gulf Oil Corporation who first published experimental observations confirming the link.6 Within a short time, demand for sonic porosity-logging applications overtook that for seismic applications.


> Illustration from the 19 3 5 patent on acoustic logging by Conrad Schlum ber ger. The el d engineer ( 13 ) w as supposed to slide a sleeve


( 17 ) until sound com ing from receivers ( 3 and 4 ) appeared to arrive sim ultaneously at each ear.


In 1960, field crews testing the VLT response in cased holes in Venezuela noticed that certain zones caused unreadable, low- amplitude signals. They correctly concluded that the anomalous signals could be attributed only to cement condition. Measuring and recording signal amplitude in addition to arrival time gave birth to an unexpected application, and CBT Cement Bond Tool logs soon replaced the temperature survey for detecting top of cement.


By the early 1960s, the first sonic tools had acquired tens of thousands of logs, and engineers set about designing a second- generation tool to address three problems: tool durability, and poor signal in the presence of


borehole irregularities and near-wellbore alteration. The tool-durability problem arose because early tools used rubber to isolate receivers from transmitters, thereby preventing undesirable sound waves from propagating within the tool and overwhelming desired signals. However, rubber tended to absorb gas from gas-rich formations, causing the tool to expand and break apart as it was brought to surface. The tool was strengthened by replacing the rubber with steel, but then the tool housing had to be shaped so that the path of sonic waves traveling through the steel would be longer than the paths through the formation and back to the receivers. (next page). Many modern sonic tools continue to


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Oilfield Review


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