Plenty of oil and gas exploration practices in faulted basins have shown that hydrocarbons are mainly distributed in fault transformation zones instead of the whole fault zone

including relay ramp

flexural turning point

intersection area and terminal

which show remarkable characteristics of migration pathways.In order to find out the advantageous conditions and mode of hydrocarbon migration in fault transformation zones

we made a systematic analysis of the characteristics of hydrocarbon migration based on the study of the formation and evolution of fault transformation zones.The results show that the fault transformation zones may serve as both lateral and vertical pathways for hydrocarbon migration at different evolution stages.When acting as lateral migration pathways

they are advantageous in terms of (1) the gradient of fluid potential

(2) well-developed sand bodies characterized by a higher probability of reservoir juxtaposition and better lateral connectivity

and (3) a relatively lower ratio of vertical to lateral permeability.There are two main modes of lateral migration:undamaged-laterally connected hydrocarbon migration and accumulation mode

and destroyed-vertically and laterally sealed hydrocarbon migration and accumulation mode

and hydrocarbon enrichment horizons are generally consistent with migration horizons.When acting as vertical migration pathways

they are advantageous in terms of (1) a higher activity intensity for the hard-linkage transformation zone

prone to be a migration pathway with episodic opening; (2) the fault plane of the hard-linkage transformation zone

usually a ridge-shaped low-potential area

favorable for hydrocarbon accumulation; (3) the stress concentration and fracture development

tending to destroy the caprock and resulting in vertical seepage.Similarly

there are also two main modes of vertical migration:incompletely destroyed-vertical hydrocarbon seepage through relay ramps

and destroyed-vertical hydrocarbon migration along fault planes

in which oil and gas tend to accumulate in shallower horizons.In addition

it can be proven that the fault transformation zone has once been the pathway of fluid migration in terms of mineral precipitation rate

diagenesis

groundwater seepage and water inrush in mine

etc.