Research And Safty Evaluation On Ultimate Discharge Capability Of Blooey Line Used In High Production Gas Well

Nowadays, gas drilling (nitrogen drilling) has become an important means of improving the penetration rate. When drilling into high-pressured rich gas reservior, wellbore destroys the initial ground stress field. The sudden release of accumulated energy can cause rock burst. Gas will flood into the blooey line through annulus with the production over1,000,000cubic meter per day. In that case, blooey line will sustain impact or vibration cause by gas flushing, which can lead to the serious accident that gas flow with cuttings pierces the blooey line within a short time. In addition, high temperature or spark caused by blooey line vibration and friction can lead to major accidents such as gas explosion and combustion. Such accidents have been witnessed at the well site and have resulted in huge economic losses and life casualties. Therefore, in gas drilling process, similar emergencies from high pressure and high production gas wells make blooey line failure a difficult problem for the developing technology. Based on this background and problem, the research goal and research content of this thesis is presented.Firstly, a large number of document literatures are investigated, collected and read about erosion study of high pressure pipe joints fluid-solid coupling and blooey line erosion failure. Then, based on the field data of174wells and194gas drilling processes from Sichuan-Chongqing and Xinjiang region, blooey line connection and failure data are collected, read and analyzed. Finally, combined with the computational fluid dynamics, fluid-solid coupling dynamics, mechanical strength and erosion theory, detailed research thought, method and content are presented. Main research contents and achievements are listed as follows.(1)Theoretical study of blooey line erosion failure mechanism and fluid-structure interaction issue is carried out. Based on the computational fluid dynamics(CFD) theory, CFD two-phase flow finite element model of high speed cutting-carrying gas eroding different joints is constructed. Meanwhile, detailed study is carried out to discuss the velocity field distribution of high speed cutting-carrying gas passing through different bending structures, trajectory of cuttings, erosion area and erosion velocity. The safety evaluation study of bending structures is also conducted via changing their main structure parameters.(2)According to the distribution of blooey line and combination modes of T-jiont and straight pipe-line in Sichuan-Chongqing region, CFD finite element model calculating the discharge capability of the whole blooey line is constructed. After the simulation of different discharge production and construction of mathematical model predicting discharge capability, a new method is put forward to calculate and predict the blooey line discharge capability of different joints, which provides theoretical basis for predicting ultimate discharge capability and blooey line safety evaluation.(3)Based on the research results of blooey line erosion mechanism and the relationship between internal pressure, instantaneous impact force, erosion and discharge capability, a method is proposed to predict the blooey line discharge capability and calculate the residual strength under different discharge conditions.(4)Based on the basic theory of fluid-structure interaction and dynamic modal analysis, dynamics theoretical study and computer simulation study of blooey line fluid--structure interaction are conducted, mathematical models calculating axial vibration and transverse vibration of blooey line fluid-structure interaction are constructed. A computer simulation model is also constructed to carry out the dynamics study of blooey line fluid-structure interaction of high production gas well in emergency. All the efforts and study have provided mathematical model and simulation model for the safety and stability evaluation of blooey line. The research results provide theoretical basis for reducing the impact on blooey line and vibration caused by high production multiphase gas flow in the wellbore, preventing fatigue damage and optimization designing the whole structure of blooey line.(5)To reduce or absorb the vibration from underground emergency, a method is proposed to install one or more vibration reduction devices or vibration absorbers which can prevent blooey line failure. A new vibration reduction or impact reduction device is designed to install on blooey line and prevent blooey line failure of high production gas wells.