<title>Computation of Stoneley wave attenuation for leak detection in large storage tanks</title>

ABSTRACT Early-warning hydrocarbon leak detection is a key to protecting groundwater from contamination by leaking storage tanks. This paper reviews the technology for vapor and liquid leak detection and evaluates methods of using it. Current technology offers both vapor and liquid hydrocarbon detectors. However, none that we tested was completely free of problems. Vapor detectors age and degrade in service. Liquid detectors lack high sensitivity. Of the different methods for early leak detection, vapor detectors respond in the shortest time. Detection systems need to be developed further to overcome remaining problems. In particular, they also need to be able to distinguish real tank leaks from normal hydrocarbon backgrounds.

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EVALUATION OF THE ACCURACY OF VOLUMETRIC LEAK DETECTION METHODS FOR UNDERGROUND STORAGE TANKS CONTAINING GASOLINE1

International Oil Spill Conference Proceedings ◽

10.7901/2169-3358-1989-1-27 ◽

1989 ◽

Vol 1989 (1) ◽

pp. 27-35

Author(s):

Joseph W. Maresca ◽

James W. Starr ◽

Robert D. Roach ◽

John S. Farlow

Keyword(s):

Data Analysis ◽

False Alarm ◽

Leak Detection ◽

Test Methods ◽

Probability Of Detection ◽

Test Method ◽

Underground Storage ◽

Storage Tanks ◽

Test Protocol ◽

Probability Of False Alarm

ABSTRACT A United States Environmental Protection Agency (EPA) research program evaluated the current performance of commercially available volumetric test methods for the detection of small leaks in underground gasoline storage tanks. The evaluations were performed at the EPA Risk Reduction Engineering Laboratory's Underground Storage Tank Test Apparatus in Edison, New Jersey. The methodology used for evaluation made it possible to determine and resolve most of the technological and engineering issues associated with volumetric leak detection, as well as to define the current practice of commercially available test methods. The approach used (1) experimentally validated models of the important sources of ambient noise that affect volume changes in nonleaking and leaking tanks, (2) a large data base of product-temperature changes that result from the delivery of product to a tank at a different temperature than the product in the tank, and (3) a mathematical model of each test method to estimate the performance of that method. The test-method model includes the instrumentation noise, the configuration of the sensors, the test protocol, the data analysis algorithms, and the detection criterion. Twenty-five commercially available volumetric leak detection systems were evaluated. The leak rate measurable by these systems ranged from 0.26 to 6.78 L/h (0.07 to 1.79 gal/h), with a probability of detection of 0.95 and a probability of false alarm of 0.05. Five methods achieved a performance between 0.19 L/h (0.05 gal/h) and 0.57 L/h (0.15 gal/h). Only one method was able to detect leaks less than 0.57 L/h (0.15 gal/h) if the probability of detection was increased to 0.99 and the probability of false alarm was decreased to 0.01. The measurable leak rates ranged from 0.45 to 12.94 L/h (0.12 to 3.42 gal/h) with these more stringent detection and false alarm parameters. The performance of the methods evaluated was primarily limited by test protocol, operational sensor configuration, data analysis, and calibration, rather than by hardware. The experimental analysis and model calculations suggested that substantial performance improvements can be realized by making procedural changes. With modifications, it is estimated that more than 60 percent of the methods should be able to achieve a probability of detection of 0.99 and a probability of false alarm of 0.01 for leak rates between 0.19 L/h (0.05 gal/h) and 0.56 L/h (0.15 gal/h), and 100 percent should be able to achieve this performance for leak rates of approximately 0.76 L/h (0.20 gal/h).

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Stoneley‐wave attenuation and dispersion in permeable formations

Geophysics ◽

10.1190/1.1442658 ◽

1989 ◽

Vol 54 (3) ◽

pp. 330-341 ◽

Cited By ~ 47

Author(s):

Andrew N. Norris

Keyword(s):

Dispersion Relation ◽

Wave Attenuation ◽

Low Frequency ◽

Water Infiltration ◽

Stoneley Wave ◽

Biot Theory ◽

Static Approximation ◽

Quasi Static Approximation ◽

Tube Wave ◽

Dynamic Description

The tube wave, or low‐frequency manifestation of the Stoneley wave, has been modeled previously using the quasi‐static approximation; I extend this method to include the effect of the formation matrix compressibility, which tends to marginally increase the tube‐wave attenuation. Using the Biot theory of poroelasticity, I develop a fully dynamic description of the Stoneley wave. The dispersion relation derived from Biot’s equations reduces in the low‐frequency limit to the quasi‐static dispersion relation. Comparisons of the quasi‐static and dynamic theories for typical sandstones indicate the former to be a good approximation to at least 1 kHz for oil and water infiltration. At higher frequencies, usually between 5 and 20 kHz for the formations considered, a maximum in the Stoneley Q is predicted by the dynamic theory. This phenomenon cannot be explained by the quasi‐static approximation, which predicts a constantly increasing Q with frequency. Instead, the peak in Q may be understood as a transition from dispersion dominated by bore curvature to a higher frequency regime in which the Stoneley wave behaves like a wave on a flat fluid‐porous interface. This hypothesis is supported by analytical and numerical results.

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