Time-shift, one of the most popular time-lapse seismic attributes, has been widely used in dynamic reservoir characterization by linking it with pressure and geomechanical changes. Therefore, it is important to select appropriate calculation methods according to different time-lapse seismic data quality and time-shift magnitude. To date, there have been various published works comparing different time-shift calculation methods and discussing their advantages and disadvantages. However, most of these comparisons are based only on synthetic tests or single field applications. As the quality of time-lapse seismic data and time-shift magnitude can vary in different fields, one method may not work consistently well for each case. In this paper, a critical comparison of three different time-shift calculation techniques (Hale’s fast cross-correlation, Rickett’s non-linear inversion, and Whitcombe’s correlated leakage method) is provided. The three methods are applied to a set of synthetic data sets that are designed to account for various seismic noise and time-shift magnitudes. They are also applied to four real time-lapse seismic data sets from three North Sea fields. The calculated time-shift results are compared with the input (in synthetic tests) or the real observations from information such as seabed subsidence and compaction (in field applications). Both qualitative and quantitative comparisons are performed. At the end, each of the time-shift methods is evaluated based on different aspects, and the most appropriate method is suggested for each data scenario. All three time-shift methods are found to successfully measure time-shifts. However, Rickett’s non-linear inversion is the most outstanding method, as it gives smooth time-shifts with relatively good accuracy, and the derived time strains are more stable and interpretable.
We present a sedimentary geochemical record of human perturbation in the watershed and related changes in trace metals (Cr,
Ni, Zn and Pb), phosphorus and abundant rock-forming elements (Al, Fe, K, Mg, etc.) in Chaohu Lake over the past 500 years,
a period spanning historical agricultural expansion and modern economic development. The record exhibited a stable terrestrial
detrital input to Chaohu Lake before ca. 1540 AD, a period with less human perturbation of the watershed, which resulted in
low and constant values of trace metals and phosphorus (TP) concentrations as well as Al, Fe, K, Mg, fine silt (<16 μm), the
chemical index of alteration (CIA) and K/Na ratio. Two periods of successive marked increases in Al, Fe, K, Mg, fine silt,
chemical index of alteration (CIA) and K/Na ratio occurred after ca. 1540 AD and 1950 AD. The former period apparently resulted
from enhanced well-weathered topsoil erosion in the watershed related to the expansion of arable land, and the latter resulted
from further enhancement of human perturbation in the watershed during the modern period. Concentrations of trace metals and
TP were positively correlated with that of the rock-forming elements and fine silt. Trace metal pollution was limited during
1540–1950 AD, according to the low enrichment factors (EFs = 0.8–1.1), when an increase in trace metal concentrations was
also linked to changes in detrital input. In addition to detrital regulation, pollution also contributed to an increase in
TP concentrations (average EF 1.4) during 1540–1950 AD and the average accumulation rate of anthropogenic phosphorus was 87.3 mg m−2 a−1. Anthropogenic phosphorus increased further and Pb and Zn pollution also occurred after 1950 AD, reaching maximum values
after 1980 AD, when the average accumulation rates of anthropogenic Zn, Pb and phosphorus (mainly in the form of NaOH-P) were
242.2, 43.3 and 811.8 mg m−2 a−1, respectively. The increase in phosphorus pollution in recent decades is probably from the domestic sewage sources of Hefei
City and non-point sources related to agricultural utilization of commercial fertilizer, whereas Zn and Pb pollution is probably
derived mainly from industrial sources of Hefei City, as deduced from their spatial variations in the sediments of the river
mouths. 相似文献