SUMMARY Radiative transfer theory is applied to the measurement of average values of the transport mean free path and absorption length (la, related to the intrinsic quality factor) in the lithosphere beneath France by comparing simulated and observed coda envelopes of regional records. The lithosphere is modelled as a flat layer representing the crust overlying a half‐space representing the mantle, with different velocities and scattering properties. We infer the average values of la (assumed to be constant over the whole medium) and transport mean free paths in the crust (l*c) and mantle (l*m) by minimizing a misfit function between observed and modelled Lg coda envelopes. This comparison is conducted in two different time windows, the whole Lg coda (group velocity smaller than 2.6 km s−1) and the early coda (vg < 2.6 km s−1 and lapse time smaller than 300 s), when coda envelopes have decay rates that depend on distance. In the early coda, a single set of parameters la and l*c minimizes the misfit function. Using the whole Lg coda time window, we find that many models fit the data equally well. We explain this difference by the common decay rate of envelopes independent of distance over most of the coda window. The measurement of the attenuation of the coherent Lg wave complements these results to constrain la and l*c. We find that a model with l*c∼ 250 km and la∼ 150 km explains the attenuation of both the direct Lg wave train and the entire Lg coda with both time and distance at 3 Hz. However, the trade‐off between the two parameters is too strong to conclude reliably on the dominance of intrinsic on scattering attenuation.

No abstract

No abstract

No abstract

No abstract

A good 4D image shows the effect on the seismic of production-related changes from within and sur-rounding a reservoir. It is well understood that the quality of 4D images is driven by two main ingredients: the quality of the acquisition and the quality of the processing. While 4D acquisition has been taking the limelight recently, the evolution of 4D processing algorithms has been steadily, and perhaps quietly, enhancing the quality of 4D images, including data acquired before the advent of carefully designed, dedicated 4D surveys. Using data from the Foinaven Field, one of three BP-operated fields in the West of Shetlands area, this paper shows how such improvements in processing technology over the last decade have enhanced the quality of the 3D imaging, the 4D seismic difference image, and improved the 4D repeatability.

No abstract

No abstract