Mechanical Safety Evaluation And Software Development Of Horizontal Well Fracturing

This paper belongs to a part of a national twelfth five year plan major projects about "complex formation leakage diagnosis and completion method research" (Number: 2011ZX05005-006-008HZ) and a project of "downhole tool string mechanics analysis and application software research" which cooperate with CCDC downhole service company PetroChina company.Now with the construction pressure, downhole temperature, hole geometry complicated and construction state diversified, the security problems and failure problems of pipe string are increasing, which hinder the development of staged fracturing technology in horizontal well. It is difficult to judge the security problem of fracturing string in horizontal well by the ways of measuring instrument or direct experiment. So far, establishment of accurate mechanical model and mathematical model based on stressing features of fracturing string under different operating conditions, and development a safety evaluation software about fracturing string mechanics in horizontal well are the most effective way. In this paper, abroad and domestic research present condition in this field was systematically analysed by studying, collection and reading lots of domestic and abroad literatures. At the same time, the existence problems of safety evaluation about fracturing string mechanic were discussed. And the major research and complete research ideas were proposed. The main research contents and results are as follows:1) First, mechanical-mathematical models of multi-packers staged fracturing was built, including mathematical-mechanical models of stress and deformation of fracturing strings under various work parameters. Calculation model of axial force and drag friction of fracturing string were built based on the measured well track data.2) Mathematical model of equivalent stress of string safety evaluation under the three axial stress combined action was deduced by Lame equation of elasticity theory and Von Mises Stress equation, which established mathematical model and strengthen judging criteria for mechanical strength safety evaluation of multi-staged fracturing string.3) As for the process of pumping into the fracturing fluid at high volume, equation of fracturing fluid pressure drop in string inner diameter reducing place was deduced. And calculation model of friction pressure drop of non-Newtonian fluid fracturing fluid was established, including the calculation mathematical model of drag friction between fracturing fluid and pipe wall, and the deformation of string caused by fluid drag friction.4) Calculation mechanical-mathematical model of relationship between lowering weight in wellhead and packer pressure in downhole was built, which provided theoretical basis for mechanical analysis and safety evaluation of packer fracturing string.5) According to four working condition of multi-staged fracturing string in horizontal well: setting, opening piston slide, and opening balling slide, the research of open hole horizontal well completion staged fracturing mechanical model was carried out, and its mechanical calculation mathematical model was built. Analytical mathematical model of string mechanics from packer to wellhead was deduced.6) According to mechanical-mathematical model of fracturing string mechanic evaluation under all kinds of working condition and different parameter in this paper, application software for multi-staged fracturing string mechanic safety evaluation in horizontal well was developed. With this software, safety operation area of casing pressure and tubing pressure in fracturing can be got, which provided theoretical basis for optimization design of multi-staged fracturing string’s safety working parameter。7) This software has applied in Sichuan oilfield, Tarim oilfield, Tahe oilfield, and achieved good results.