Study On The Geological Characteristics In Hailar Oilfield Based On Mini-fracturing Testing

Hailar is rich in oil and gas resources and is an important area for exploration and development of Daqing Oilfield.However,because of the complex geological conditions,the reservoir is buried deep,the structure is developed and the reservoir types are various,so it is easy to appear sand plugging in fracturing.In order to further optimize the main fracturing design,improve the fracturing sand ratio,reduce the sand plugging rate and obtain better construction results,it is necessary to clarify the geological characteristics and characteristic formation mechanism of fracturing in Hailar Oilfield before construction.The rock type and mineral composition characteristics of the reservoir were analyzed by using polarizing microscope,X-ray diffraction whole rock analysis and X-ray diffraction clay mineral content analysis.The rock cementation type and cementation method of the main reservoir were analyzed by rock sample thin sheet identification.The rock mechanics parameters of the reservoir were measured based on triaxial compression,brittleness evaluation,ground stress test,tensile strength test and fracture toughness test.The closed stress and gradient,friction resistance,permeability and filter loss coefficient of high stop pump well are analyzed by FracproPT software,and the crack initiation and extension characteristics are simulated.The results show that the lithology of each reservoir in Hailar Oilfield is variable,the maximum of clay mineral content in Nantun formation is 20.4%;in general,calcite,iron dolomite and clay cementation,point-line contact is dominant;Young's modulus of rock is mainly concentrated in the range of 0.761×104MPa?4.380×104MPa,the Poisson's ratio is 0.228?0.388,the maximum brittleness of reservoir in Nantun formation is up to 0.7920,average maximum minimum level principal stress difference 6 MPa,the tensile strength is 10.75MPa,the fracture strength is 0.54 MPa·m0.5;the gradient of instantaneous stop pump is 0.0180MPa/m?0.0269MPa/m,and the closed stress distribution is mainly in the range of 0.0154MPa/m?0.0232MPa/m,the flexural friction is distributed from 1.42MPa?14.36MPa,and the perforated hole eye friction is mainly concentrated between 1.5MPa?3.0MPa,the permeability is distributde between0.014×10-3?m2?0.520×10-3?m2.The analysis shows that the reservoir fracturing geological characteristics of Nantun formation are:high stop pump pressure,closed stress;large range of closed stress gradient,strong heterogeneity of in-situ stress;large range of bending friction change,with strong heterogeneity;Nantun formation is a very low permeability reservoir,developed a certain natural fracture,physical heterogeneity is stronger;natural fracture,multi-fracture formation filtration coefficient is larger.The small test combined with triaxial rock mechanics test,structural stress of fault block reservoir and analysis of rock mineral composition have proved that the Nantun formation is a high closed stress reservoir with high construction pressure and high stop pump pressure.The high content of gravel,tuff and muddy,the structural stress caused by the development fault,the large minimum horizontal principal stress and the toughness characterized by high young's modulus and poisson's ratio are the main causes of the high stop pump pressure.