Study On The Characteristics Of Cretaceous Faults In Block M Of Pakistan

The research was about the structural character research and structural evolution analysis of M Block in Lower Indus Basin, Pakistan, based on the new 3D seismic data, following the direction of the theories such as structural geology, petroleum geology, sedimentology and so on. This dissertation mainly includes the tectonic setting, fault character, tectonic evolution and the relationship between structural character and oil-gas accumulation. Following is the results of the research.The faults are very developed in M block, which are normal faults and can be divided into 3 classes:the second class faults controlled the structural belts; the third class faults controlled the structures; the forth are the minor faults. On the vertical section, the fault association styles include "y" and inversed "y"-type, step type, horst and graben type; on the horizontal slice, the fault association styles include parallel-aligned type faults, en echelon faults and skew-type faults. The structural character of M block is horst and graben alternating developed, controlled by the tectonic activities. The M block can be divided into 4 structural belts:from west to east, there are western graben, western horst, middle graben and eastern horst. The structural belts are controlled by the secondary class faults, which are the top class faults in M Block.Based on the tectonic evolution sections, the tectonic history of M block is subdivided into four phases:from early Jurassic to early Cretaceous is the rifting period:from middle to the late Cretaceous is strike-slip extensional period when the massive normal faults were formed; from late Cretaceous to Paleocene is the depression period:in the late Paleogene is Himalaya rising period.The oil-gas accumulation area is influenced by the faults, in M block, three types structural trap are most favorable. The up-thrown fault nose and block controlled by faults in minor horst are the structures with rich accumulation of oil and gas. having a good exploration prospect.