Investigation of thin bed strata using borehole image log and high resolution seismic data.

摘要

Thin-bedded (0.1 cm to 10 cm) deepwater deposits from the Miocene Mount Messenger Formation, New Zealand were investigated using borehole image logs and high resolution seismic data with the purpose of studying how certain geophysical methods can be used in the analysis of thin-bedded reservoirs. Sandstone and shale bed boundaries were detected with the Fullbore Formation MicroImager(TM)1 log using automated sliding window and threshold techniques. Bed boundaries are detected by filtering the logs using the difference between the vertical moving averages of microresistivity. Maxima and minima on this filtered log represent depths at which there is a vertically persistent, abnormal change in the microresistivity values and if exceeding a specified threshold are taken to represent a bed boundary.; Hurley's (1996) Modified Fischer Plots are used to correlate relatively conformable successions of genetically related beds in subsurface reservoirs and to provide information about the stratigraphic thinning and thickening of sediments in a given well at a variety of vertical scales. These plots, when derived from automatically detected bed boundaries using the method developed in this dissertation, vary with threshold, and lead to different stratigraphic interpretations. A Modified Fischer Plot with zero threshold closely resembled the manually-computed plot from the same dataset.; The degree of seismic anisotropy in a layered medium depends on the contrast in elastic properties between layers and the nature of the layering. In the case of these thin-bedded turbidites, the layer properties are relatively similar, and the layers are so thin relative to a seismic wavelength that the thickness and periodicity of the layering have little influence on the seismic properties. As layering affects the frequency content of seismic data, the hypothesis that differing types of thin-bedded strata (i.e. channel-fill vs. distal levee beds) would exhibit significant differences in seismic frequency spectra was investigated. Conventional spectral decomposition of seismic data did not prove to be useful in interpreting thin bed strata; however, seismic data resolution was enhanced through analyzing peak frequency versus bed thickness allowing for an easier and clearer interpretation of sets of these thin bedded turbidites.; 1Trademark of Schlumberger.