Tectonic Characteristics of Tan-Lu Fault Zone (East China) in the South of Bohai Sea Area and Its Controls on Hydrocarbon Accumulation

Abstract

Tan-Lu Fault Zone (TLFZ) is a giant, continental strike-slip fault zone in the East China that cuts across the whole Bohai Sea Area, controlling the distribution of different types of traps, and it directly or indirectly controls about 70% of oil and gas distribution in Bohai Sea Area. Based on latest and detailed 3D seismic interpretation, coherence time slice, curvature time slice and 3D visualization techniques, and combining with previous research results, this paper studies tectonic characteristics of TLFZ and reveals its controls on hydrocarbon accumulation in the South of Bohai Sea Area. The result shows that TLFZ is mainly NNE trending fault zone in the South of Bohai Sea Area, and it can be divided into three different groups according to their positions, and each group contains three different branch faults. However, the strike-slip deformation intensity is stronger gradually from west group to middle group and east group. It also exists obvious differences among these branch faults in spatial pattern. Though all the branch faults are continual, subparallel, high angle or vertical faults in deep area, most of them are en echelon faults and others are absent in shallow area, which implies that TLFZ has experienced multiple evolution stages. Through geometry analysis, fault activity rate calculation and balanced section analysis of branch faults in TLFZ, three different evolution stages can be identified during Cenozoic, ranging from intense extensional deformation to intense dextral shear with intense extensional deformation and weak dextral shear with weak extensional deformation. As a result, different types of restraining and releasing bends are formed due to the strike slip of branch faults in TLFZ, and these restraining and releasing bends play a great role in hydrocarbon accumulation. Several large commercial oilfields (BZ25-1, BZ34-1 BZ34-2/4 and KL6-5 oilfield) have been discovered in restraining bends, but in releasing bends there are few oilfields, which indicates that restraining bends are more favorable to hydrocarbon accumulation than releasing bends in the South of Bohai Sea Area. In addition, the strike-slip deformation intensity of branch faults have influence on hydrocarbon accumulation, as intense strike-slip deformation is favorable to the development of secondary faults that can destroy the formation of traps, which is consistent with the fact that there are more oilfields in the west and middle group than the east group of TLFZ.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019