Study On Characteristics And Prediction Of Cracks In The Fourth Member Of Xujiahe Formation In Central

Based on the current research achievements, the drilling data, logging data, field outcrop investigation, core observation, FMI interpretation and production test, with the theoretical guidance of structure geology, petroleum geology and reservoir geology, this thesis studied the fracture characteristics and prediction of the4th member of Xujiahe formation in the central Yuanba area. The following knowledge and achievements have been obtained in this thesis:The central Yuanba area has mainly undergone late Yanshan tectonic movement and Himalayan tectonic movement since late Triassic epoch. There mainly developed tectonic fracture in the4th member of Xujiahe formation, the main types of fractures are low angle shearing fractures and high angle shearing fractures, accounting for45%and30%respectively, horizontal and vertical fractures are25%of the total fractures; the length of fractures is medium size, both the width and density are small, fracture spacing is big, and the fractures are mainly small width ones. The fracture filling degree is mainly unfilled and half-filled fracture, accounting for65%, full filled fractures are35%of the total fractures; calcite and asphaltene are the main types of fracture fillings, second are carbonaceous and argillaceous.The main orientations of the fractures in the4l member of Xujiahe formation are NW direction and NEE direction, followed by nearly SN direction and NE direction. There are two stages of fractures in the study area. The first stage is the NW and NE direction plane shear fractures, The second stage is the nearly SN and NEE direction plane shear fractures and a few NW direction sectional shear fractures; the NW direction fractures are consistent with the NWW-SEE direction of current terrestrial stress, and the effectiveness of those two directions of fractures are the better. The fracture development degree is influenced by tectonic stress, tectonic position, lithology and thickness of the stratum.The result of paleo-tectonic stress field numerical simulation indicated that the I level fracture development zones distribute in the area of fault nose structure, intersection position of several fault belts, hinge zones and the end of the faults; the II level fracture development zones distribute in the area of clamped position of faults and high points of structure. Fracture development areas are distributed in the areas of YB9-YB3-YB5, YL301H-YL1-YL29, YL3-YL28,YL31,YL4-YL16.Comprehensive researches indicate that fracture development advantageous zones of the4th member of Xujiahe formation in the central Yuanba area are mainly the I level fracture development zones along the NW direction faults and the fault nose structure.