The role of faults in hydrocarbon migration

It is well known that the hydrodynamic behaviour of faults may be rather different from that of their surrounding beds. These characteristics may not be constant through time for a single fault and especially change during rupture events. Various numerical tests were performed using the TEMISPACK software to calculate the quantity of hydrocarbons that can migrate through damaged zones with high permeability in and near to a fault. The paper examines the influence on fluid flow of (1) the thickness of the fault zone, (2) the connectivity between fault and carrier beds, and (3) the opening time when permeability increases sporadically. The results confirm the importance of fault zones on hydrocarbon migration. Even when very narrow (2 meters), temporarily open (<100000 years), and moderately permeable (<10 mD), faults focus the migration of hydrocarbons. The flow is stronger in narrow, temporary faults but the quantities in circulation remain essentially the same. The nodes of the migration paths are the connections between faults and carrier beds (and/or source rock). This connection has a greater influence on the quantity of migrating hydrocarbons than does the intrinsic permeability of the fault. Given major hydrocarbon losses in the rock's porosity, thick drains are less efficient than are narrow zones for bringing the hydrocarbons to the reservoirs.