While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km(3) in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (10(4) km(3)) and passive margins globally (3 x 10(5) km(3)). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages.

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Seismic compressional and shear velocities are uniquely sensitive to the elasticity of the Earth and are used to estimate many properties of interest in oil exploration, reservoir development, and production efforts. Such properties include formation lithology, porosity, saturation, mechanical properties, presence of fractures, principal stresses, pore pressure, and formation damage. Logging while drilling (LWD) acoustic tools can be used when Wireline acoustic logging is prohibitive and/or real-time decisions based on acoustics are needed. It has been shown that modern LWD acoustic tools with powerful, specialized acoustic transmitters can deliver most acoustic data and products with the same quality as their Wireline counterparts. However, there is a lot of variation in the quality of traditional LWD acoustic data depending on the tool design. The operator’s decision to run an LWD acoustic tool is not an easy one though as the tool is often the most complicated and the longest part of the drill string. In this paper we present the field test results of a “sourceless” LWD acoustic tool that uses seismic energy generated by the drill bit to extract formation elastic properties instead of a powerful, specialized transmitter. Such a tool may consist of a receiver section of hydrophones only, which compared with traditional LWD tools, significantly simplifies the mechanical design, shortens the length of the tool, and reduces the tool cost. In the absence of an active transmitter, continuously recording the drill bit energy as the drill bit rotates enables maximizing the signal-to-noise ratio (SNR) of the formation arrivals. In addition, the presence of azimuthally distributed receiver elements at each receiver axial position permits decomposition of the received wavefield into monopole, dipole, and quadrupole components. Processing results of the sourceless tool using time and frequency semblance are compared to those from a traditional LWD acoustic tool in the same well to demonstrate the viability of the concept. We also demonstrate that in the case of “traditional” LWD acoustic tools it is beneficial to place the tool transmitter below the receiver array. In this case the drill bit energy propagating along the borehole is “added” to the energy generated by the source and effectively increases the frequency bandwidth of the source signal and improves the SNR of the resulting formation arrivals.

Seismic compressional and shear velocities are uniquely sensitive to the elasticity of the Earth and are used to estimate many properties of interest in oil exploration, reservoir development, and production efforts. Such properties include formation lithology, porosity, saturation, mechanical properties, presence of fractures, principal stresses, pore pressure, and formation damage. Logging-while-drilling (LWD) acoustic tools can be used when wireline acoustic logging is prohibitive and/or real-time decisions based on acoustics are needed. It has been shown that modern LWD acoustic tools with powerful, specialized acoustic transmitters can deliver most acoustic data and products with the same quality as their wireline counterparts. However, there is a lot of variation in the quality of traditional LWD acoustic data depending on the tool design. The operator’s decision to run an LWD acoustic tool is not an easy one, though, as the tool is often the most complicated and the longest part of the drillstring. In this paper, we present the field test results of a “sourceless” LWD acoustic tool that uses seismic energy generated by the drill bit to extract formation elastic properties instead of a powerful, specialized transmitter. Such a tool may consist of a receiver section of hydrophones only, which compared with traditional LWD tools, significantly simplifies the mechanical design, shortens the length of the tool, and reduces the tool cost. In the absence of an active transmitter, continuously recording the drill-bit energy as the drill bit rotates enables maximizing the signal-to-noise ratio (SNR) of the formation arrivals. In addition, the presence of azimuthally distributed receiver elements at each receiver axial position permits decomposition of the received wavefield into monopole, dipole, and quadrupole components. Processing results of the sourceless tool using time and frequency semblance are compared to those from a traditional LWD acoustic tool in the same well to demonstrate the viability of the concept. We also demonstrate that, in the case of “traditional” LWD acoustic tools, it is beneficial to place the tool transmitter below the receiver array. In this case, the drill-bit energy propagating in the formation along the borehole is “added” to the energy generated by the source and effectively increases the frequency bandwidth of the source signal and improves the SNR of the resulting formation arrivals.