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The Experimental Modeling for Faults and Strata Sealing: Mechanism and Impact to Hydrocarbon Entrapment

Zha, Ming 1; Qu, Jiangxiu 1; Wu, Kongyou 1
1 Department of Petroleum Resources, China University of Petroleum, Qingdao, China.

The faults and strata seals have a significant control on hydrocarbon migration and accumulation in lacustrine basins of China. However, the mechanism and impact of these seals are various and complicated. Based on analyzing geological settings of Jiyang depression, Bohai Bay basin of China, and combinations of different faults and strata, several modeling experiments have been designed to simulate the sealing of fault - connective sand body and fault - lenticular sand under the conditions of steady (continual) and non-steady (periodic) injection of hydrocarbon.

The experiments showed that migration pathway was not homogeneous in 3-D span, but an “express way” for hydrocarbon movement along with more permeable sequences. Due to different sequences and lithology, the periodic accumulation and release of migrating energy resulted in oil pulsant migrating into reservoirs (sands). The oil injecting velocity and mode affected its saturation in reservoirs. Favorable oil accumulation took place in upper sequences when steady injecting, and oil was trapped in sands near the infilling inlet when non-steady injecting, which reveals that traps close to source rocks would have a priority to accumulate hydrocarbon. Moreover, the main driving force for oil migration was buoyancy in steady injection, but high pressure in non-steady injection. The obliquity and tortuosity of oil carriers were also important controlling factors for active hydrocarbon migration and accumulation. When a carrier had sharp obliquity and a little tortuosity, oil migrated crossing the fault plane towards lower porous sands and was sealed there, otherwise, oil moved laterally along sands distributed on both sides of the fault. Generally, lithologic traps connected by faults are more probable to entrap petroleum, or have higher oil filling capacity than lenticular sands, which means that the driving mechanism and pathways have an important impact on migration and sealing. Within Tertiary layers of Jiyang depression, more than 95% spaces are filled with oil in lithologic traps connected by fault, demonstrating the significance of fault connecting and strata sealing.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009