Transfer Zones and Their Significances from Hydrocarbons in the Offshore Bohai Bay Basin, Eastern China
The Bohai Bay basin is a Cenozoic rift basin with a rhombus-shape and an area of about 200,000 square kilometers. The basin is situated on the eastern coast of China, and intensely influenced by the Tan-Lu fault system. There are numerous faults of varying strikes and scales in the offshore Bohai Bay basin. The NE-, NW- and EW-trending wrench and normal faults are predominant.
Besides the isolated faults, there are also many intersecting segmented faults by hard and soft linkages in the offshore Bohai Bay basin. Consequently, various types of transfer zones had developed in the overstepping normal faults. According to the dips and assembling characteristics of normal faults, three types of soft linkages of normal faults have been classified in the study area, including the synthetic overstepping, convergent conjugate overstepping and divergent conjugate overstepping. Their corresponding transfer zones are relay ramps, oblique anticlines and horsts, respectively. The displacement-distance scaling demonstrates that the zones transferred the extensional strains and made the three-dimensional strain conversation among the segmented normal faults. Based on the degree of interaction and linkage between the overstepping segments, the evolutionary stages of the transfer zones could be divided into four phases: (1) isolated faults, (2) initial formation, (3) complication, and (4) broken.
Up to now, some important oil and gas discoveries in the transfer zones have been achieved in the offshore Bohai Bay basin, such as the JZ25, JX1, LD27 and LD10 fields, and so on. The integrated analysis shows that the significances of the transfer zones on hydrocarbon accumulations in the study area involve their influences on the traps formation, sedimentary systems distribution, reservoirs properties and hydrocarbon migration, etc. The traps in the transfer zones are the favourable objectives for oil and gas exploration in the offshore Bohai Bay basin.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009