Experimental investigation of episodic oil migration along fault systems

Abstract Simulation experiments of episodic oil migration along an open fault have been conducted with 2-D experimental models.The results show that episodic oil migration along a fault zone has the following characteristics in comparison with steady oil migration. (1) During episodic migration, overpressure or stress forced oil to first enter the lower part of sand beds underlying mudstones. Following oil accumulation in large quantities in this part, oil charged into the upper part of sand beds overlying the mudstones where a small amount of oil accumulated. When enough oil was available for charging, the accumulated oil volume in the upper (above mudstone) and lower sand beds (below mudstone) gradually became equal; (2) More oil passed through the fault zone when oil migration proceeded in an episodic fashion; (3) During episodic migration, oil migrated vertically and laterally in the sand beds on both sides of the fault zone. It seems that oil migrated along various directions without preference. The pathways are fairly wide and the whole sand bed can act as the pathway. In addition, the migration is relatively fast. We infer that the essential reason for these observations is that overpressure or stress is the main driving force for oil migration during the episodic.