Fracture reopening by micro-earthquakes, a mechanism for oil seepage in mildly active rifts: a case study from Gemsa oilfield, the southern Gulf of Suez rift, Egypt

Episodic hydrocarbon seepage is present at Gemsa oilfield, southern Gulf of Suez rift, Egypt. The occurrence of the oil at this area has been known for thousands of years. The nature and origin of this seepage is the main target of the present study. Surface geological mapping substantiated by subsurface mapping using 2-D seismic lines and well log data are integrated. Moreover, the present day stress orientation and magnitudes are integrated with the mechanical properties of the reservoir rock in order to produce a coherent interpretation for the migration pathways and the main causes of the hydrocarbon seepage. The study revealed that the episodic hydrocarbon seepage at mildly active rifts such as the southern Suez rift can be resulted from the migration of entrapped hydrocarbons along the damage zone of slightly active faults with continuous micro-earthquakes. The pressure released from the micro-earthquakes causes the reopening of preexisting fractures where hydrocarbon found their easy pathway to the surface through highly fractured rocks and unconsolidated sediments. The produced migration pathway map proposes the possibility of an unexplored Hammam Faraun Member reservoir at the study area. The original oil in place of the predicted reservoir is estimated to be more than 22 MMBO which encourages the design makers for more investigation of this reservoir to increase its certainty and putting it in the plan of the future investments.