Research On The Hydraulic Fracturing Mechanics Theory Of Tuffaceous Formation In Hailaer Oilfield

Tuffaceous formation in Hailaer basen, which is one of the most important exploration and development tracts during the Eleventh Five-Year Plan period, storages rich petroleum resources. Its low-porosity and low-permeability induce poor natural productivity. In addition, its structures and lithological characters are very complex which make the conventional stimulation technologies unsuitable in the situation. Furthermore, sand plug occures frequently during the hydraulic fracturing operations, which could lead to poor proppant concentration and even operation failure. According to these conditions, a series of studies are proceeded and valuable results are achieved in this paper.Firstly, the lithological, electrical and sedimentary characters of the formation are described systematically in the paper. The mineralogical characters of the tuffaceous formation are analyzed by means of slice identification, X ray diffraction, SEM and so on. The enhydrous character is studied by waterlogging test. The orientation and value of formation stress are acquired by anisotropic wave velocity test, viscous remanence method, borehole caving, ASR test, differential strain method and mini-frac test. Based on the analysis, it is shown that the lithological characters of the formation are very complicated and the clay mineral content is high. The alkaline formation is sensitive to the water which induces soften and dispersion of formatin rock and it is adverse for hydraulic fracturing operation, but the others are stable to the water.Secondly, the mechanics parameters of tuffaceous formation rock are acquired by density measurement test, Brazilian test, uniaxial compression test and triaxial compression test. Based on the distributing randomicity of the defects inside the tuffaceous rock, CDM and statistical intensify theory, the constitutive equation is established in the paper.Thirdly, considering the influence of in situ stress, fluid pressure and infiltration of fracturing fluid, the borehole stress field model is deduced and the breakdown pressure calculating model for open-hole completion and conventional completion are established. The maximal intensify criteria of I-II mode fracture propagation is established based on the stress distribution and fracture mechanics. The model is testified by finite element software.Fourthly, the fracture width model, fluid flow model, fracture height propgating model and continuum model are established in the paper. The fracture geometric parameters can be calculated by iterative method.This paper combines the fracture mechanics, damage mechanics with tuffaceous formation characters; accomplishes the experimental analysis and academic study; and researches systematically the hydraulic fractur ing mechanics theory. Based on aboved work, the powerful theoretical instructions and technical support can be supplied for effective development of tuffaceous formation in Hailaer oilfield. Moreover, it has important academic value and realistic meaning.