Application of 3D anisotropic CSEM inversion offshore west of Greenland

Lovatini, A.; Watts, M. D.; Umbach, K.; Ferster, A.; Patmore, Steve; Stilling, J.

doi:10.1190/1.3255880

Cited by 8 publications

(3 citation statements)

References 8 publications

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“…In addition, stacked reservoirs or reservoirs with interbedded shales will exhibit significant anisotropy. The marine CSEM community variously ignores anisotropy or declares it to be all-important ͑for examples of the latter, see Jing et al, 2008;and Lovatini et al, 2009͒. In the context of the previous section, this turns out to be correlated with the use of 1D/2D inversion and interpretation or 3D inversion and interpretation. Referring again to Figure 6, the radial fields might be expected to be sensitive to the vertical resistivity, and the azimuthal fields sensitive to the horizontal conductivity.…”

Section: Anisotropymentioning

confidence: 99%

Ten years of marine CSEM for hydrocarbon exploration

2010

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Marine controlled-source electromagnetic ͑CSEM͒ surveying has been in commercial use for predrill reservoir appraisal and hydrocarbon exploration for 10 years. Although a recent decrease has occurred in the number of surveys and publications associated with this technique, the method has become firmly established as an important geophysical tool in the offshore environment. This is a consequence of two important aspects associated with the physics of the method: First, it is sensitive to high electrical resistivity, which, although not an unambiguous indicator of hydrocarbons, is an important property of economically viable reservoirs. Second, although the method lacks the resolution of seismic wave propagation, it has a much better intrinsic resolution than potential-field methods such as gravity and magnetic surveying, which until now have been the primary nonseismic data sets used in offshore exploration. Although by many measures marine CSEM is still in its infancy, the reliability and noise floors of the instrument systems have improved significantly over the last decade, and interpretation methodology has progressed from simple anomaly detection to 3D anisotropic inversion of multicomponent data using some of the world's fastest supercomputers. Research directions presently include tackling the airwave problem in shallow water by applying time-domain methodology, continuous profiling tools, and the use of CSEM for reservoir monitoring during production.

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Section: Anisotropymentioning

confidence: 99%

Ten years of marine CSEM for hydrocarbon exploration

2010

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“…(Broadside CSEM data are also sensitive to horizontal conductivity, but such data are not available here.) Thus, if there is any anisotropy in the sedimentary section at Gemini there will be an incompatibility in the CSEM and MT data sets, similar to the incompatibility of inline and broadside CSEM modes (e.g., Lovatini et al, 2009). Constable (2010) notes that when fitting CSEM data to better than 10%-15%, the assumption that inline data are only sensitive to vertical resistivity is likely to break down, especially if using amplitude and phase at multiple frequencies.…”

Section: Isotropic Joint Cesm/mt Inversionsmentioning

confidence: 99%

And the geophysicist replied: “Which model do you want?”

2015

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Marine controlled-source electromagnetic (CSEM) and magnetotelluric (MT) soundings were carried out between 1997 and 2003 over the Gemini prospect in the Gulf of Mexico during early development of marine instrumentation. The resulting data sets provide a good test bed for examining the effect of the data type and misfit choice on regularized inversion solutions. We inverted the data sets individually and jointly for isotropic and anisotropic resistivity at a variety of data misfits. We found that multifrequency CSEM inversions vastly improved structural resolution over single-frequency inversions, suggesting that variation in skin depth added significant information. Joint MT and CSEM inversion appeared to improve resolution over MT-only inversions at depths considerably deeper than the CSEM data can resolve, probably by constraining shallow structure in the parts of the model to which the MT data were sensitive. The addition of model anisotropy improved data fit, but introduced an arbitrary scaling between the regularization penalty on model roughness and the penalty on anisotropy. A small relative penalty on anisotropy produced two independent models for horizontal and vertical resistivity, whereas a large penalty reproduced the isotropic models. Intermediate penalties produced pleasing models, but there was no objective criterion to choose one particular model. Inverted models also depend significantly on the choice of target data misfit, but the optimum misfit is difficult to determine even with well-estimated errors. So-called L-curves do not provide an objective choice of misfit because they are both heuristic and depend on the choice of data that is plotted. Various measures of structure in data residuals were tested in an attempt to guide the misfit choice, with some success, but this too was somewhat heuristic. Ultimately, of the 100 or so inversions that were run, no single model could be considered "preferred," but together they provided a good understanding of the information contained in the data.

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“…Jing, Green and Willen (2008) showed, using 3D modelled anisotropic data at three frequencies (3/8, 5/8 and 7/8 Hz), that 3D anisotropic inversion of the data is feasible and gives results that are consistent with the synthetic data. Lovatini et al (2009) applied 3D anisotropic inversion to both synthetic data and real conventional controlled source EM data west of Greenland at two frequencies (0.25 Hz and 0.75 Hz) and obtained very good fits to the data at those frequencies.…”

Section: O N C L U S I O N Smentioning

confidence: 99%

Multi‐transient electromagnetic repeatability experiment over the North Sea Harding field^‡

Ziolkowski

Parr

Wright

et al. 2010

Geophysical Prospecting

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A B S T R A C TWe present results of synthetic time-lapse and real repeatability multi-transient electromagnetic surveys over the North Sea Harding field. Using Archie's law to convert porosity and fluid saturation to resistivity we created 3D isotropic models of the reservoir resistivity at different stages of production from the initial state in 1996 through to complete hydrocarbon production by 2016 and, for each stage, we simulated an east-west transient electromagnetic survey line across Harding. Unconstrained 1D full-waveform Occam inversions of these synthetic data show that Harding should be detectable and its lateral extent reasonably well-defined. Resistivity changes caused by hydrocarbon production from initial pre-production state to production of the oil rim in 2011 are discernible as are significant changes from 2011-2016 during the modelled gas blowdown phase.The 2D repeatability surveys of 2007 and 2008 tied two wells: one on and the other off the structure. Between the two surveys the segment of the field under investigation produced 3.9 million barrels of oil -not enough to generate an observable time-lapse electromagnetic anomaly with a signal-to-noise ratio of 40 dB. Processing of the 2007 and 2008 data included deconvolution for the measured source current and removal of spatially-correlated noise, which increased the signal-to-noise ratio of the recovered impulse responses by about 20 dB and resulted in a normalized root-meansquare difference of 3.9% between the data sets. 1D full-waveform Occam inversions of the real data showed that Harding was detectable and its lateral extent was also reasonably well-defined.The results indicate that the multi-transient electromagnetic method is suitable for exploration, appraisal and monitoring hydrocarbon production.

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Application of 3D anisotropic CSEM inversion offshore west of Greenland

Cited by 8 publications

References 8 publications

Ten years of marine CSEM for hydrocarbon exploration

Ten years of marine CSEM for hydrocarbon exploration

And the geophysicist replied: “Which model do you want?”

Multi‐transient electromagnetic repeatability experiment over the North Sea Harding field^‡

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Application of 3D anisotropic CSEM inversion offshore west of Greenland

Cited by 8 publications

References 8 publications

Ten years of marine CSEM for hydrocarbon exploration

Ten years of marine CSEM for hydrocarbon exploration

And the geophysicist replied: “Which model do you want?”

Multi‐transient electromagnetic repeatability experiment over the North Sea Harding field‡

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Product

Resources

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Multi‐transient electromagnetic repeatability experiment over the North Sea Harding field^‡