Research On Strength Check And The Safety Evaluation For Multi-packers Fracturing Strings In Horizontal Well

In the oil and gas exploration technology continues to further study process, highly productive reservoirs are less and less, a large number of low productivity of the reservoirs is drilling now. Whether efficiently develop low capacity oil and gas fields is that we should be focused on and overcame, but also the focus of attention. Due to the disadvantages (Low total reserves/Low productivity can/Low pressure) of the low productivity of the reservoirs, we should continue to fracture and inject water during the production of the oil. In order to solve the low-permeability reservoirs highlighted various issues, starting in the 1980s horizontal well fracturing technology came into being, and now began to develop rapidly. Drilling of horizontal Wells is increasing, and the corresponding completion string mechanics analysis research also has become an important object of people’s study, according to well completion string mechanics analysis to provide better guidance to the production operation has become the consensus.By reading a lot of literature, the previous of horizontal well for the fracturing string mechanics research almost all focus on the buckling deformation, friction resistance and whether the multi-packers fracturing string can be successfully tripped into the target layer and picked up. Aimed at the study of the strength check and the safety evaluation for multi-packers fracturing string in horizontal well is not enough. In this paper hopes to focus on the specific conditions of multi-packers fracturing strings in horizontal well, doing some research on strength check and the safety evaluation for multi-packers fracturing strings in horizontal well.First of all, against the study of the strength check and the safety evaluation for multi-packers fracturing string in horizontal well to establish a fracturing fluid-string-formation unsteady heat transfer mathematical model of the temperature field.Then by an iterative calculation repeatedly, through the entire period of operation, and finally, establish a temperature field in the range of a whole well of string, the media of annular space and the formation radial of the entire working time. By prediction of wellbore temperature field, time is considered the main factors of temperature. From the beginning of the job, the declining trend of the borehole temperature is significantly. As time goes on, the wellbore temperature change is decreased, the difference of the temperature between the borehole and formation gradually is zero.The relationship between temperature and the different interval of the well track (vertical segment/building up section/horizontal segment) in the multi-packers fracturing string in horizontal well is significantly not the same:horizontal hole section of the fracturing fluid temperature increased the most obvious, the vertical interval of fracturing fluid temperature rise in the minimum.Then through the study of fracturing construction of the multi-packers fracturing string in horizontal well in various effect, we should consider the influence of the piston force in the process of the changing string axial. By this study, providing a theoretical basis to prevent pipe string in advance releasing, channeling sealing and other dangerous of malignant failure, reducing security and reliability of packer pipe string.In order to study the interaction force of the pipe string and packers, the different types of pipe string structure divided into three kinds of mechanical model, including free movement pipe string, finite moving pipe string and restrict the movement of pipe string.In order to evaluate the strength and security of different pipe string structures, and to optimize the design of horizontal well fracturing string multi-packer system, the completion pipe string is divided into single tubular column and composite pipe string type, under the consideration of the interaction of packer and tubing. Suggest that the use of the software has a guiding significance because of the study in the effect of different types of structure, obtained by force and deformation of a single Pipe string, in a variety of Pipe string.Through the study of the multi-packers fracturing string in horizontal well proposed mechanical model of multi-packer completion strings. The multi-packer Pipe string is converted to a similar single composite packer and a single packer to analyze the situation, concluded the relation between the interaction and the changes in length of the tubes and the packers in the multi-packers fracturing string.Combined with specific completion operations, researched the relationship between the axial force and the changes in length of the tubes in the specific construction such as tripped into the target layer and picked up, setting proceed and fracturing time in the multi-packers fracturing string multi-packers fracturing string, and established the axial force,stress and the stretch mathematical model under the influence of buoyancy and gravity in the specific construction.Taking into account the pipe thermal stress during strength check and safety evaluation, established a mathematical model considering the thermal stress. Von-Mises theory combined with research on the dangerous points of the tubing, gives the basic equations of the completion string strength check. Under the different string structure, analysis software could analyze the stress and the safety in the different construction work, and provide a good guidance for subsequent completion pipe string design and operation and construction.Under the specific condition of the well, evaluated the strength and the safety of the completion string. The completion of the fracturing string is determined at various stages of fracturing operations are safe and reliable, can meet production needs.In the process of an optimization design on the fracturing string, the calculated and analysis results are presented that the dangerous points of the tubing is still in the position of the well top by the software. Comparison with the advantages and disadvantages between the single tubular column and composite pipe string, suggested that using tubing (17.26kg/m) instead of part of lower segment tubing(20.09kg/m) is better than the single tubular. It presented that the dangerous points of the tubing is still in the position of the well top by using the software, but security coefficient increased from 1.8617 to 1.8617, reduced the overall weight of the string, enhance the security of the tubing string, the string was optimized as well.