The Column Mechanical Analysis Of A Trip Column To Partial Pressure Two-tier

The coalbed methane reservoir in China buried in shallow,generally500-1500m.And it has the unique features of low gas saturation and low permeability,low pressure,strong heterogeneity,micro-fracture development.The forming conditions and the mechanism of hydrocarbon accumulation,reservoir characteristics,pressure systemsand,and gas production mechanism are all significantly different from conventional gas reservoir.Tn order to obtain industrial production, fracturing has become one of the main technical measures to improve the yield of the reservoir. For general fracturing, generally only one layer can get the effect.In the fracturing multilayer operation on the need for multiple fracturing, the complex cycle is long, difficult, and the high cost of construction. If we can achieve a trip to the column partial pressure two or more levels, you can increase the relevance of fracturing,overcome the multi-layer, thickness, vertical heterogeneity serious impact, give full play to the capacity of each layer,make reservoir capacity to be fully released, reduce operating costs and can improve operating efficiency. Therefore, a trip to column of large displacement pressure of a two-tier column design is very necessary.In this paper, the design of a trip to column partial pressure column of a two-tier is studied. In the fracturing process, the column weight, hole curvature, temperature, and external pressure, the viscous friction resistance moment, and the packer force anchoring forces and other load combinations role,will cause the string deformation in a certain stress level. In a variety of downhole conditions and operating conditions, column force, stress and working conditions constantly change. If stress or deformation is too large,it will cause the column destruction and other job accidents.Especially in the large displacement fracture process, the throttle pressure will easily make the column broken off at some parts, and because of the large displacement downhole tools are easily structural deformation to impact of the construction. CBM fracturing to improve reservoir flow capacity and increase the efficiency of drainage gas has seen significant results. CBM per day is relatively low (2000square/day), generally using low-cost strategy, the general fracturing is water fracturing.But water carrying sand performance is poor, which requires the fracturing displacement very large (greater than6square), or it is likely to cause the sand in the fracturing process submerged in the well bore to form a sand plug fracturing failure.Coupled with multi-reservoir micro-cracks and large missing, it also requires a large displacement. In the large displacement fracturing process, due to the large displacement in the column wall surfaces a great frictional resistance will have, while the large throttle pressure happening in the column to shrink the diameter, so that the force of column is complex,which easily leads to the column broken off at some parts. In particular of the multi-column, a lot of downhole tools under the well, greatly reduced diameter lead to an increase in throttle pressure, which requires downhole tools have good pressure resistance, and the sand fluid erosion capability of large displacement, or it is easy to form expanding for downhole tools, structural deformation and affect the fracturing operation. In addition, for large displacement, the column suffered on the top edge, if the anchor role of downhole tools anti jacking force is not enough, which may result in the column movement of fracturing failure. Therefore, the research in mechanical behavior of fracturing string friction, load, stress and deformation in the fracturing conditions, can provide a scientific basis for the rational allocation of the hierarchical sub-combination of fracturing string and a reasonable choice of operating parameters.The same time, working conditions alternation will be directly caused the tubing, the outside temperature and pressure change, and will inevitably lead to the force and deformation of the packer tubing string changing, further impact on the tubing strength and packer sealing effect.This stress analysis of trip column is very important, which can provide a basis for the strength check of security, improvement of the fracturing process and carring out smoothly and can guide the on-site construction,to ensure the fracturing of construction safety, improve the fracturing operation rate.And it has the great significance in the process of promoting the development of coalbed methane resources.In this article, the mechanical analysis of the fracturing string of coalbed methane wells is studied, of which the packer is the most critical and the core tool in the sectional fracturing string, its performance directly related to the success or failure of the fracturing operation.The application of node method,the balance equation in the packer is established by theoretical calculations to identify the packer seal stability, to ensure the column strength check of security,at the same time to identify the weak link of the column to be improved, and come to the best construction parameters,give a fracturing operation guidance to guide the selection and design of downhole tools,to provide the basis for the smooth fracturing process.In this paper the following aspects are carried out:(1)Collection, research, analysis the tubing string at home and abroad, a separated control system stress analysis theory to understand the research status of the downhole string;(2)The structure analysis of fracturing string with one trip column of large displacement pressure of a two-tier;(3)The mechanical analysis of the fracturing string with the trip string voltage divider two layers of large displacement, the establishment of mechanical model of fracturing string;(4)The theory of mechanical calculation and analysis of fracturing string, fracturing the lower conditions, the following packer for the study, the force analysis, the establishment of equilibrium equations;(5)Combine with the characteristics of the underground column process, the application of non-steady-state heat conduction theory, the establishment of the temperature field calculation model; using fluid mechanics to solve the problem of oil wells in column liquid friction, the establishment of the pressure field calculation model;(6)Calculation temperature and pressure anywhere in the fracturing conditions; application of downhole string software, the stress analysis at the packer of a combination of fracturing string, strength check; column stability calculation, the fluid flow friction computational analysis, the axial load calculation and analysis;(7)Combined with the guidance of the scene, assess the research results.In this paper, the mechanical research of downhole string which uses theoretical calculations to determine the balance of stability of the packer, deduces underground column load, stress, deformation calculation method, provides a basis for the rational design of the downhole string and producing reasonable parameterschoose.The computational analysis of pressure field are carried out, can calculate the pressure value of any segment column,which are more accurate parameters for the column stress analysis. Column does not move, due to various tools, the column is divided into several small pieces.After the packer, packer and hydraulic anchor can not move.This paper analyzes a small section of the force and focus on fracturing the lower, analyzes all the forces on the particle for the packer as a particle, and the criterion of the packer not moving is proposed. At the same time, in the column into the bottom of the well process, temperature, pressure change in the environment will lead to the column length change, so the position of the column into the well is not accurate.This paper analyzes the factors affecting the column change in the column into the bottom of the well process and gives the formula and draws up the program, so you can easily and accurately the card position, exactly packer formation. For general fracturing monolayer, due to the downhole string structure relatively simple, string force is also easy to analysis.But the partial pressure of a two-tier column is mechanical analysed in this paper,for the voltage divider two-tier underground column structure and the partial pressure of two underground pipe string above the layer structure is similar,so the findings of this article also has a great reference to the mechanical analysis of the partial pressure of more than two underground column.