AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Oil Accumulation Modeling in the Young Traps During Fault Activation: An Example of Tanlu Fault Zone in the Southern of Bohai Sea, China
(1) Exploration and development research insitute of CNOOC. Ltd Tianjin, Tianjin, China.
The Tanlu fault zone is the largest and most active zone in the southern of Bohai sea in China, and is a main hydrocarbon accumulation area in Bonan field with oil reserves greater than 3×108 tons (1.97×109bbl). A great number of late active faults and young traps appeared in the Tanlu fault zone after 5.1Ma. Structural traps were not finally shaped until about 2.0Ma. These traps hydrocarbon accumulation were significantly different.
Source rock simulation and crude oil samples from the Bonan field in the Tanlu fault zone were analyzed to determine the origin and formation mechanisms of large-medium size oil field. Regional seal and fault activity rate modeling are used to simulate the response of a relatively complex set of traps and to investigate hydrocarbon preservation risk for young traps in the Tanlu fault zone.
Three accumulation model including enrichment traps, depletion traps and dynamic equilibrium traps exist in the Tanlu fault zone, each of which has a distinct reservoir forming factors assemblage. The oil accumulation rate greatly exceeded the rate of oil loss resulting from in-reservoir biodegradation and vertical leakage through faults in enrichment traps of the active fault zone. Late-stage hydrocarbon generating and focusing from a large area of source rocks, fault activity rate middle (activity rate <25m/Ma), and thick mudstones in the Miocene Minghuazhen Formation are key reservoir forming geologic factors in enrichment traps. The complexity of the sealing surface morphology on the positions of migration pathways caused the trap to be shielded of oil originating from the adjacent source rocks, and high fault activity rate (activity rate >25m/Ma) caused the oil loss of fault zone, resulting in oil depletion in a young trap of the active fault zone. Dynamic equilibrium traps often formed low abundance and medium-sized reservoirs as lack of a regional cap rock. The oil accumulation rate and the rate of oil loss in the active fault zone were controlled by generation of source rocks, fault activity rate and regional seal during fault activation.