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A hydrocarbon indicator (HCI) or direct hydrocarbon indicator (DHI), is any seismic attribute found via reflection seismology that indicates the presence of hydrocarbons in an oil or gas reservoir. DHIs are particularly useful in hydrocarbon exploration for reducing the risk of exploration wells. DHIs most commonly occur as bright spots, a local high amplitude anomaly which are displayed with bright colors so as to stand out from background amplitude variation, or as flat spots, which are horizontal reflectors that cross existing stratigraphy and indicate a hydrocarbon fluid level within an oil or gas reservoir. Dim spots, or low amplitude anomalies, may also serve as DHIs. Polarity reversals can occur where the capping rock has a slightly lower seismic velocity than the reservoir and the reflection has its sign reversed.〔 An indication of gas is when the amplitude of a reflection increases with the angle of incidence. Normally it would decrease.〔 Equipment prior to the 1970s had the bright spots obscured due to the automatic gain control. They are easier to observe in unconsolidated sediments, such as Tertiary basins. These basins are likely to be offshore but close to continents.〔 ==See also== *Amplitude versus offset 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hydrocarbon indicator」の詳細全文を読む スポンサード リンク
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