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|Title:||A STOCHASTIC STUDY OF THE PROPERTIES OF SYNTHETIC SEISMOGRAMS CHARACTERISING SUB-SURFACE LITHOLOGY|
EARTH SCIENCE ENGINEERING
|Abstract:||The ever increasing thirst for energy by mankind has till now been largely quenched by natural resources like oil, gas and coal. With rapid industrialization and technological progress, it has become very important to explore and exploit newer avenues of these resources, before the existing ones are completely depleted. The importance of oil amongst the natural resources of energy was evident during the recent energy crisis which.led to a vigorous exploration for hydrocarbons in diffe-rent sub-surface environments. Oil is confined to structural traps, stratigraphic traps or a combination of these two (1) . Structural traps are relatively easy to locate by seismic exploration methods and since most of them have already been located, the oil industry is searching for stratigraphic traps to satisfy the increased demand for oil. A stratigraphic trap is one in which the chief trap making element is some variation in the stratigraphy or lithology, or both, of the reservoir rock, such as facies change, variable local porosity and permeability, pinchouts, lenticular sands, shop string sands, sand bars, channels and lenses, cavities, reefs, and unconformities (1) . -2 Stratigraphic traps seldom have any relation with either overlying or underlying reservoirs, but may be repeated later-ly (1). Stratigraphic phenomena generally extend over wide areas or along elongated trends, and the discovery of one sand bar, channel filling, sand patch, or organic reef therefore, strongly suggests that others will be found in the regions But, most structural effects of local stratigraphic phenomena are small and difficult or impossible to interpret correctly. Even after discovery, there are few clues to the size of the pool, or the direction in which it will extend; strati-graphic pools infact, are frequently a succession of surprises. In stratigraphic exploration we look for shoe string sand, sand patches, facies changes, distributory channels or organic reefs as the cause of the trap (1). The conventional method of seismic data interpretation can, under simple geologic conditions give indications of stra-tigraphic traps like angular unconformities and pinchouts, but can rarely delineate sandy zones, sand bars, channel lenses etc., which in general show completely, random distribution (1) . Stratigraphy is difficult to. resolve by conventional seismic interpretational methods. However, with the recent improvements in field methods seismic instrumentation and data processing techniques, the quality of reflection records has improved remarkably (10) . For this reason the seismic method -3- can be used with reasonable success for mapping the subsurface lithology and for the exploration of stratigraphic traps, pro-vided new and proper interpretational strategies are devised and adopted. Seismic stratigraphic exploration may then be used to determine the gross stratigraphy as well as the local lithological variations. Synthetic seismograms have made it possible to analyze and account for events recorded in the field as reflections in the absence of noise. The synthetic seismogram is a theoretical solution which gives the idealized response of a given strati-graphic sequence to an excitation by a seismic impulse. The analysis of theoretical seismograms would allow a correlation of the seismic signal with the stratigraphy which contributed to that signal. Thus, a stratigraphic sequence may be evolved based on the observed seismograms with the aid of the synthetic seismograms.....|
|Appears in Collections:||MASTERS' DISSERTATIONS (Earth Sci.)|
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