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Srnka, L, Constable S.  2018.  Marine Electromagnetic Methods – Present and Future. Geophys. Soc. Houston J.. 8   10.1190/segam2017-17632803.1   Abstract

Since industry began funding marine electromagnetic (EM) methods in the 1980s, tremendous progress has been made in applying these methods not only to hydrocarbon exploration but also to a wide range of applications. After more than two decades of excitement and investment, many successes and some failures, marine EM use has now greatly diminished due to a combination of factors, including resolution and depth limitations, imaging uncertainties, perceived high costs, difficulties in business integration, and the recent down cycle in hydrocarbon markets. Fortunately, acquisition costs are declining due to the arrival of continuously towed systems, subsurface depths of investigation are increasing, and cooperative seismic-EM inversions are beginning to produce better estimates of lithologies and fluids, including for marine hydrates. Enabled by the technical progress made in deep water for hydrocarbon use, offshore EM is expanding to other applications. Virtually any EM onshore application is now a candidate for the offshore. These include permafrost, geothermal, minerals, contaminant mapping, and groundwater investigations. Offshore EM methods are now firmly installed in the geophysical toolkit, and their uses will grow.

Chavez, L, Altobelli S, Fukushima E, Zhang TS, Nedwed T, Palandro D, Srnka L, Thomann H.  2015.  Detecting Arctic oil spills with NMR: a feasibility study. Near Surface Geophysics. 13:409-416.   10.3997/1873-0604.2015023   AbstractWebsite

To meet the world's growing energy needs, the oil industry is pursuing oil resources in ice-prone regions. These activities will require robust oil spill contingency plans. One area of need is a method to remotely detect oil that is trapped beneath or within ice. The current operational method for oil detection within or under ice requires placing personnel on the ice to take measurements. A primary challenge with these measurements is the speed at which they can be collected. Presented here is a scaled-down prototype of an Earth's field nuclear magnetic resonance device that can be moved from one spot to another on the ice by a helicopter to quickly survey large areas. This small-scale version has been built and tested. It successfully differentiates an oil surrogate from the bulk water signal by using an adiabatic inversion, followed by a delay to suppress the otherwise overwhelming water signal before acquiring the signal after an adiabatic half passage. The device will be scaled up, and further testing will be conducted. Initial proof-of-principle results show great promise for the development of a remote oil detector.

Constable, S, Srnka LJ.  2007.  An introduction to marine controlled-source electromagnetic methods for hydrocarbon exploration. Geophysics. 72:WA3-WA12.   10.1190/1.2432483   AbstractWebsite

Early development of marine electromagnetic methods, dating back about 80 years, was driven largely by defense/military applications, and use for these purposes continues to this day. Deepwater, frequency-domain, electric dipole-dipole, controlled-source electromagnetic (CSEM) methods arose from academic studies of the oceanic lithosphere in the 1980s, and although the hydrocarbon exploration industry was aware of this work, the shallow-water environments being explored at that time were not ideally suited for its use. Low oil prices and increasingly successful results from 3D seismic methods further discouraged investment in costly alternative geophysical data streams. These circumstances changed in the late 1990s, when both Statoil and ExxonMobil began modeling studies and field trials of CSEM surveying in deep water (around 1000 m or deeper), specifically for characterizing the resistivity of previously identified drilling targets. Trials offshore Angola in 2000-2002 by both these companies showed that CSEM data can successfully be used to evaluate reservoir resistivity for targets as deep as several thousand meters. Both companies leveraged instrumentation and expertise from the academic community to make swift progress. The resulting rapid growth in the use of marine EM methods for exploration has created a demand for trained personnel that is difficult to meet; nevertheless, at this time, CSEM data represent a commercial commodity within the exploration business, and acquisition services are offered by three companies. The ability to determine the resistivity of deep drilling targets from the seafloor may well make marine CSEM the most important geophysical technique to emerge since 3D reflection seismology.

Srnka, LJ, Carazzone JJ, Ephron MS, Eriksen EA.  2006.  Remote reservoir resistivity mapping. The Leading Edge. 25:972-975.   10.1190/1.2335169   AbstractWebsite

Marine controlled-source electromagnetic (CSEM) surveying has emerged as a new tool for remotely detecting reservoired hydrocarbons offshore. Industry is now evaluating this technology and the business value of the information that it provides. When integrated carefully with other geoscience information, primarily seismic data, marine CSEM shows promise for adding considerable value in upstream applications, at least in clastic environments. In this article, we review some of the history of CSEM development for the offshore oil and gas industry, show a few examples from recent ExxonMobil surveys, and then look ahead into a possible future for the technology.

White, BS, Kohler W, Srnka LJ.  2001.  Random scattering in magnetotellurics. Geophysics. 66:188-204.   10.1190/1.1444894   AbstractWebsite

Typical well logs show substantial variations of formation electrical resistivity over small spatial scales, down to the resolution of the logging tool. Using a plane stratified earth model, we examine the effects of this fine-scale microstructure on scattering of the naturally occurring electromagnetic (EM) waves used in magnetotellurics, We show how 1-D magnetotelluric (MT) data may be viewed as arising statistically from a smoothed effective medium version of the resistivity-depth profile. The difference between the data produced by the true medium and the effective medium is attributable to random scattering noise. This noise is fundamental to magnetotellurics and other diffusive-wave EM exploration methods since it arises from the very small spatial scales that are usually ignored. The noise has unique statistical properties. which we characterize. We show that if scattering is the dominant noise source, a thin layer of increased resistivity at depth can be reliably detected only if the noise statistics are incorporated properly into the detection algorithm. This sets a new fundamental limit on the vertical detection capability of MT data. The theory agrees well with Monte Carlo simulations of MT responses from random resistivity microlayers.

White, BS, Kohler W, Srnka LJ.  2001.  Random scattering and the detection capability of the magnetotelluric method. Iutam Symposium on Mechanical and Electromagnetic Waves in Structured Media. 91:31-42.   10.1007/0-306-46955-3_3   AbstractWebsite

Typical well logs show that formation electrical resistivity varies substantially as a function of depth in the earth. These variations consist typically of slow-scale macroscopic changes or trends, modulated by rapid variations due to fine scale layering. The rapidly varying resistivity fluctuations are significant in amplitude and occur over small spatial scales, down to the resolution of the logging tool. Using a plane stratified earth model, we examine the effects of this fine scale microstructure on the scattering of the naturally occurring electromagnetic waves used in magnetotellurics (MT). We show theoretically how MT data are influenced by the multiscale nature of the formation resistivity. MT data may be viewed as arising largely from a smoothed "effective medium" version of the resistivity vs. depth profile. The difference between the data produced by the actual medium and that produced by the effective medium is due to scattering noise arising from the layering microstructure. We model this fine scale layering as a rapidly varying stochastic process. This scattering noise component of MT data is fundamental since it arises from the very structure of the medium being probed. This noise is substantial at frequencies above approximate to 0.1 Hz and has unique statistical properties, which we characterize. We assess the impact of this noise upon the detectability of a thin layer of increased resistivity at depth. We show that the theory agrees well with Monte Carlo simulations.

Demirbag, E, Çoruh C, Costain J, Carazzone J, Srnka L.  1993.  Elastic inversion of Gulf of Mexico data. Offset-Dependent Reflectivity—Theory and Practice of AVO Analysis. ( Castagna JP, Backus MM, Eds.).:285-314.   10.1190/1.9781560802624.ch5   Abstract

The estimation of P- and S-wave seismic velocities and densities of earth layers from the data sets recorded at the surface has long been one of the main research interests in reflection seismology. Although structural interpretations of the subsurface with sophisticated data processing and interpretation techniques have been facilitated, there remains a lot more to be done in obtaining quantitative information about the seismic parameters to lead to lithological interpretation that will open the ways to direct hydrocarbon exploration, groundwater exploration, and understanding the deep earth crust.

Warren, RK, Srnka LJ.  1992.  Exploration in the basalt-covered areas of the Columbia River Basin, Washington, using electromagnetic array profiling (Emap). Geophysics. 57:986-993.   10.1190/1.1443324   AbstractWebsite

The electromagnetic array profiling (EMAP) exploration method was tested at three basalt-covered locations on the Columbia Plateau in central Washington state. Three 16 km survey lines were located to intersect test wells drilled by Shell. The data were EMAP filtered, and inverted using a nonlinear 1-D Riccati approach developed for conventional magnetotelluric (MT) processing. Large and small features on the resulting resistivity cross-sections produced by EMAP filtering near the drill hole closely approximated the electric induction logs. Sedimentary units within the survey area appear to be thin, with some thickening indicated toward the center of the basin. Structuring within the sediments is mild within the limits of the survey, although there is appreciable structure within the Miocene flood basalts on one test line.

Srnka, LJ.  1987.  Riccati inversion of magnetotelluric data. Geophysics. 52:381-381.   10.1111/j.1365-246X.1987.tb05221.x   AbstractWebsite

We have developed a new 1-D inverse scattering method to invert magnetotelluric data. This method, which we call Riccati inversion, is direct (non-iterative), fully non-linear, and accommodates very broad bandwidths. A form of the 1-D MT response function is used that satisfies a first-order non-linear partial differential equation of the Riccati type. Properties of the solutions to this equation in the complex frequency plane v = i-w is the real frequency, are used to derive the conductivity profile at each depth. An ansatz that has the same analytic properties as the data is used in the computer implementation of the algorithm. The inversion has two parts: fitting the ansatz to the surface data using appropriate constraints, followed by downward evolution (layer stripping) and extraction of the conductivity at each depth. The process is regulated by controlling the structure of the ansatz. Tests on forward model data with the Riccati method showed good agreement with the model. It is also more robust than the smooth C2+ Gel’fand-Levitan integral algorithm developed by Parker. We have applied the Riccati inversion method to MT data obtained over volcanic terrain on the Columbia Plateau of southern Washington State. The inverted results are in good agreement with induction log data from a nearby exploration well.

Hood, LL, Sonett CP, Srnka LJ.  1984.  Lunar Magnetism. Nature. 307:661-662.   10.1038/307661a0   AbstractWebsite
Srnka, LJ, Runcorn SK.  1983.  Planetary Exploration - Probing the Lunar Interior. Nature. 301:15-16.   10.1038/301015a0   AbstractWebsite
Schultz, PH, Srnka LJ.  1980.  Cometary Collisions on the Moon and Mercury. Nature. 284:22-26.   10.1038/284022a0   AbstractWebsite
Schultz, PH, Srnka LJ.  1980.  Cometary Collisions on the Moon and Mercury - Reply. Nature. 287:86-87.   10.1038/287086b0   AbstractWebsite
Srnka, LJ, Hoyt JL, Harvey JVS, Mccoy JE.  1979.  Study of the Rima Sirsalis lunar magnetic anomaly. Physics of the Earth and Planetary Interiors. 20:281-290.   10.1016/0031-9201(79)90051-7   Abstract

The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10−3 G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of ∼10−5 – 10−4 G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length.

Srnka, LJ, Martelli G, Newton G, Cisowski SM, Fuller MD, Schaal RB.  1979.  Magnetic-field and shock effects and remanent magnetization in a hyper-velocity impact experiment. Earth and Planetary Science Letters. 42:127-137.   10.1016/0012-821x(79)90198-5   AbstractWebsite

The impact of aluminum projectiles onto high-alumina terrestrial basalt blocks at 13–15 km s−1 in the presence of a variable magnetic field has been studied. Low-frequency search coil data show that plasma is produced. causing local compression of the ambient field. Although field production is expected, it was not detectable with the existing apparatus. Measurements of the remanence of the shocked basalt show that magnetization was acquired in the material near the craters. The acquired remanence is predominantly soft, but also contains a component not demagnetized by 500 Oe AC field treatment. Material shocked in a 10-Oe vertical field exhibits inverse dependence of magnetization upon distance from the crater center. Examination of the shocked basalt in thin section reveals a general lack of shock metamorphism in the material surrounding the crater, except for the presence of a high-pressure melt glass which was splashed onto the crater walls. Micro-probe analyses show that the glass is a whole-rock melt of fairly uniform composition, and is contaminated with aluminum from the projectile. The mineralogical data support the view that the acquired magnetization is shock remanence, since negligible shock heating occurred in the magnetized material. These results bear on the problem of lunar magnetism, suggesting that shock effects or possibly thermoremanence in ejecta fragments may be responsible for part of the magnetization of the lunar surface.

Srnka, LJ, Mendenhall MH.  1979.  Models of an early lunar dynamo. Lunar and Planetary Science Conference. 3:2343-2355., Houston, Tex.: Pergamon Press, Inc. Abstract

The hypothesis that a dynamo once existed in the moon, and hence was the source of lunar paleomagnetism, is tested using a model for the global thermoremanent magnetization of spherical lithospheres. Various models of an ancient lunar dipole field are used which incorporate intensity variations and reversals, and which are consistent with lunar sample paleointensities. It is found that non-reversing lunar dynamos which have simple exponential decay histories beginning at 4.6 b.y. ago are inconsistent with this limit, unless the moon has been thoroughly demagnetized to a depth of tens of kilometers by impacts or other processes. An early lunar dynamo cannot be excluded by global scalar measurements unless the permanent lunar dipole moment is shown to be significantly less than 10 to the 13th power G/cu cm by future spacecraft measurements, which may be technologically impossible; vector measurements of lunar magnetic anomalies over the whole moon offer a possibility of determining the source of the field which magnetized the lunar crust.

Srnka, LJ.  1979.  On the detection of lunar volatile emissions. Nature. 278:152-153.   10.1038/278152a0   AbstractWebsite
De, BR, Srnka LJ.  1978.  Effect of nuclear electric quadrupole-moments in thermonuclear fusion plasmas. Plasma Physics and Controlled Fusion. 20:503-510.   10.1088/0032-1028/20/6/002   AbstractWebsite

Consideration of the nuclear electric quadrupole terms in the expression for the fusion coulomb barrier suggests that this electrostatic barrier may be substantially modified from that calculated under the usual plasma assumption that the nuclei are electric monopoles. This effect is a result of the nonspherical potential shape and the spatial quantisation of the nuclear spins of the fully stripped ions in the presence of a magnetic field. For monopole-quadrupole fuel cycles like p-11B, the fusion cross-section may be substantially increase at low energies if the protons are injected at a small angle relative to the confining magnetic field.

Srnka, LJ, De BR.  1978.  Spin-related magnetism of inter-stellar grains. Astrophysical Journal. 225:422-426.   10.1086/156504   AbstractWebsite

The magnetic dipole moments and internal magnetic fields due to the spin of electrically charged elongated nonmagnetic interstellar grains in kinetic equilibrium with their surroundings are computed for the grain-size range from 0.01 to 1.0 micron. It is shown that the induced magnetic moments and internal magnetic fields of charged spinning nonmagnetic grains of arbitrary composition and prolate spheroidal shape can be appreciable, possibly even exceeding 0.01 emu/cu cm for 0.01-micron grains. The results indicate that virtually all grains smaller than 0.1 micron in mean diameter, and all elongated grains smaller than about 1 micron in length, are immersed in local magnetic fields due to spin that are much larger than the ambient galactic field. Some implications of this effect are discussed in relation to the polarization of starlight by aligned dust grains and the primordial remanent magnetization found in primitive carbonaceous chondrites.

Srnka, LJ.  1977.  Critical velocity phenomena and LTP. Physics of the Earth and Planetary Interiors. 14:321-329.   10.1016/0031-9201(77)90182-0   AbstractWebsite

When the relative velocity between magnetized plasma and neutral gas exceeds a critical value, the gas-plasma interaction is dominated by collective phenomena which rapidly excite and ionize the neutrals. The interaction of the solar wind with a large cloud (1024 – 1028 neutrals) vented from the moon should be of this type. Line radiation from such an interaction can yield an apparent lunar surface brightness rivaling reflected sunlight levels over small areas, if the kinetic energy flow density of the gas is sufficiently high. The aberrated solar wind flow past the moon would enhance the visibility of such interactions near the lunar sunrise terminator, supporting the statistical studies which indicate that the “Lunar Transient Phenomena” (anomalous optical phenomena on the moon) are significantly correlated with the position of the terminator on the lunar surface.

Srnka, LJ, Martelli G.  1977.  Spontaneous magnetic field generation in hypervelocity impacts. Transactions-American Geophysical Union. 58:1179-1179. AbstractWebsite

Hypervelocity impacts of meteoroids onto early planetary surfaces may have generated short-lived magnetic fields. The high specific power densities of the impacts, plasma production in the ejecta clouds, and the chemically layered targets of the meteoroids are analyzed in describing the evolution of the magnetic fields. Durations from about one millionth of a minute to one minute, as well as strengths up to 100 tesla, are posited for the impact-generated magnetic fields. The analogy of magnetic-field generation in laser-target experiments is also mentioned. The acquisition of shock remanence and thermoremanence by the ejecta and nearby rock following impact is discussed.

Srnka, LJ.  1976.  Global Thermoremanent Magnetization of Planetary Lithospheres. Transactions-American Geophysical Union. 57:271-271. AbstractWebsite
Srnka, LJ.  1976.  Magnetic dipole moment of a spherical shell with TRM acquired in a field of internal origin. Physics of the Earth and Planetary Interiors. 11:184-190.   10.1016/0031-9201(76)90062-5   Abstract
Srnka, LJ.  1976.  On the global TRM of the lunar lithosphere. Lunar and Planetary Science Conference. 3( Kinsler DC, Ed.).:3357-3372., Houston, TX: Pergamon Press, Inc. Abstract

A global thermoremanent magnetization (TRM) theory is developed which takes into account the direction and magnitude of a hypothetical source dipole field, the distribution of magnetic permeability and the coefficient of TRM and the cooling rate in the lithosphere, and models the low-field TRM characteristics of the material. When applied to the moon in conjunction with lunar magnetic parameter ranges now available, the theory gives a permanent lunar dipole moment which is uncertain to a factor of about 10 to the 5th power.