Research On Low Temperature Foam Flushing Fluid Used In Frozen Soil Layer Drilling

In recent years, countries around the world are accelerating the pace of development of new energy resources, exploitation of rich resources are often accompanied by poor conditions. The existing data show that gas hydrate mainly exists in permafrost strata(frozen rock strata) and seabed sediments. The permafrost regions in China are mainly distributed in the Tibetan Plateau and Mohe County basin, the area of frozen soil area is wide, and low developed, which has high scientific research and economic value. Since the 60’s of last century, the research and development process of the frozen soil region in China has been accelerated. However, there are many problems in the construction of drilling in frozen soil area, Such as: The flushing fluid into the well temperature and the temperature difference between the inside of the hole which leads to the upper and lower parts of the borehole temperature distribution is not uniform; The difficulty of the preparation of the flushing fluid caused by the ambient temperature difference; After freezing, the rheological property of the flushing fluid is poor, and the carrying capacity is reduced, which seriously affects the drilling efficiency; In the special hole drilling(permafrost or local corrosion, variable hole section), the protective capability poor flushing fluid is easy to cause the hole section core hydration expansion. These problems directly lead to the lack of core, borehole collapse, buried drilling, pump and other accidents to increase the probability of serious interference with normal drilling, resulting in the construction progress is difficult to guarantee. Reducing the disturbance of the low temperature flushing fluid to the temperature field of the original frozen soil layer so as to ensure the good stability of the borehole wall is a difficult problem to be faced during the drilling and sampling in the permafrost regions. The experience of natural gas production in the frozen soil region of Russia shows that, the flushing fluid of small heat transfer coefficient, big amount loss of water, large viscosity has best effect. The foam flushing fluid system has the performance parameters,so under the premise of the correct selection of drilling tools and drilling technology, it is necessary to find out the influence of low temperature foam flushing fluid on the temperature field of frozen soil, which is necessary to ensure wellface stability in permafrost regions. The specific research contents and results are as follows:1)According to the law of conservation of energy, the differential equation of heat conduction in the frozen soil is derived, the relationship between heat conduction, thermal radiation and heat convection between the inner wall and the borehole wall is discussed. The flushing fluid circulation and static wellbore temperature distribution model was established. Using ANSYS numerical simulation analysis software, analysis of the bubble into the well temperature and foam velocity and bubble density related parameters of frozen soil wellbore temperature field were investigated, found that: bubble into the well temperature and foam density is the main factors affecting borehole temperature.2) The indoor temperature field testing platform was established, and the experiment was designed by orthogonal test method, and the parameters of the foam fluid were changed to detect the temperature change of the frozen soil wall layer. The experimental results show that the main factors affecting the temperature of the frozen soil layer are the foam density and the foam temperature, and the second is the bubble velocity. The correctness of the numerical simulation results is verified by experiments.3) Through a lot of experimental research, the low cost and good salt resistance of non ionic APG0810 as foaming agent of foam flushing fluid was selected,the mechanism of metal ion stability of PAM/XC composite foam stabilizer was studied,under the condition of high concentration of metal ions, a compound stabilizing agent with good viscosity, rheology and stability is obtained.4) The development of low temperature foam flushing fluid was successfully applied in the construction of Mohe County frozen soil zone and has been verified by practice, a good foam flushing fluid for drilling construction in frozen soil region was provided...