Formation and evolution of concealed fault zone in sedimentary basin and its reservoir-controlling effect

摘要

Concealed fault zones are a type of weak deformation fault zones that form in sedimentary covers and have expressive forms. This paper introduces an effective way to identify such structures according to the distributions of reservoirs, sedimentary facies, sub-sags (or sags) and salients (or ridges), and classified concealed fault zones into five types according to their scales, i.e., trap-scale, sub-sag-scale, sag-scale, depression-scale and basin-scale and characterised their structural features. Concealed fault zones go through five consecutive evolutionary stages, from the initiation of induced fractures (R shears), to the development of localised en echelon faults (R fault), to the appearance of discontinuous main faults (Y faults), to interconnected Y faults that accommodate the strike slips of basal faults, and finally to a through-going revealed strike-slip fault. Case studies show that oil-gas reservoirs often distribute as en echelon, string-or band-like features in concealed fault zones, so they might be promising oil-gas exploration targets in the future.