QI quantifies reservoir conditions and incorporates other sources of rock property data. Throughout the modern history of exploration geophysics, the evaluation of conventional reservoirs (i.e., those driven by porosity and fluid saturation) primarily involved the imaging of stacked seismic data to identify trapping mechanisms such as anticlines and faults from which hydrocarbon accumulation can occur. This concept started to evolve in the early 1990s when prestack time migration (PSTM) became commonplace and the concepts and pitfalls of amplitude vs. offset (AVO) started to become widely known. Shortly thereafter, exploration for Class II AVO anomalies became in vogue after the easy Class III "bright spots" were discovered and drilled, some of which only turned up high porosity sands or fizz gas.
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