The Anomaly of Three Simultaneous Low Parameters as an Indication of Hydrocarbons—An Example of Seismic Lithological Exploration
Huang Xude, 1989. "The Anomaly of Three Simultaneous Low Parameters as an Indication of Hydrocarbons—An Example of Seismic Lithological Exploration", An Overview of Exploration Geophysics in China — 1988, Zhao Jingxiang, Wang Yanjun, Fu Xuexin, Stanley H. Ward
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Research on seismic lithological exploration was undertaken in a small depositional depression in the northern part of Jiangsu Province. The reflections from reservoir rocks are characterized by low velocity, low frequency, and low amplitude, i.e., three simultaneous low parameters. The target is lower Tertiary clastic rocks in which the velocity of sandstone is much higher than that of mudstone, while the velocity of oil-saturated sandstone is lower than that of water-saturated sandstone. The reservoir rocks appear as a low velocity interval on a pseudo-log profile, and also in a precise interval velocity analysis with Dix's equation. The complex trace analysis gives rise to profiles of three instantaneous attributes. Further processing of the instantaneous frequency data reveals that the frequency of the top reflection of the reservoir fu decreases during the transit from the clean rocks to the reservoir rocks, so does the frequency difference between the top and bottom reflections Δf. This decrease typifies low frequency absorption in reservoir rocks. That the reservoir rocks appear to be low amplitude on an instantaneous amplitude profile is proven by synthetic seismology. A dim spot is the essential characteristic of an oil-saturated sandstone within a clastic sequence. The bright spot in this region corresponds to volcanic rocks. The prediction of a fault-sheltered structural trap advises that the high potential of hydrocarbon is at the lower altitude of the structure which is consistent with the anomaly of three simultaneous low parameters. A structure-fault-lithology composite reservoir was verified by drilling. Based on the research of the whole depression, 61 anomalies were found, stratigraphic interpretation was undertaken, and the petrographic paleogeography map was obtained. The confidence degree of hydrocarbon presence was appraised and a drilling project proposed according to the consistency of the three simultaneous low parameters, their positions in structures and the paleogeographic environment, the thickness of the target, and the size of the trap.