Theoretical And Experimental Research On Gas-Sand Two-phase Flow In Natural Gas Exploration

In natural gas exploration, sand production is one of the most seriousproblems that endangered gas well. Research on the flow behavior of gas-sandtwo-phase helps to know more about their mutual acting and flow regulation inpipelines. Then more scientific plans to remove sand, diminish equipmentabrasion and cut cost could be work out to achieve the efficiency and safety in gasproduction and exploration. On a general survey of relevant aspects of sand production and currentresearch status, the following research efforts are developed in this paper: 1. Most experts regard the velocity of fluid as the direct factor of theascending or settling of the sand carried by fluid in vertical pipelines and did a lotof research on it. In this paper the forces on the sand in fluid, on which the formerresearch is not systematic, are regarded as the key point to decide upon the motionstate. So forces on sand carried by natural gas in pipe is analyzed thoroughly.According to different granule Reno number, drag force, the most important forcein sand ascending, is found larger under high pressure than under normal pressure.It is of the same magnitude with granule body-force. Buoyancy, which is usuallyneglected in two-phase flow research, cannot be neglected under high pressure?Supported by the key project of the Ministry of Education " A Study on Oil-Gas Multiphase Flow and TheDrag Reduction in Pipes"[No. (2000) 00108]. IV摘 要and heavy gas density in mineshaft. Pressure gradient force, which is caused bydifferential pressure of the top and toe of a well, is also found non-neglectful insand ascending, though of a lower magnitude than granule body-force. Primaryresearch of forces on liquid drops carried by gas flow in flowing back gasexploration and conditions of their strain, polymerization and shattering are alsodone in this paper. 2. Based on the gas dynamics theory, condition of pressure and flow quantityat well top and geometrical condition of choke, analysis and calculation ofvelocity and pressure field at choke in pipe are completed in this paper. Inengineering and literature, whether the flow is critical or not is decided bytheoretical pressure ratio at choke. But measured value of real pressure in somegas fields and analysis in this paper show the inaccuracy of this method. Someasuration of sound velocity is presented here. According to the relationshipbetween cross sections of pipe, velocity at choke is analyzed and calculated. Theconclusion can be drawn after comparing with the local sound velocity. Moreover,flow at choke under critical or supercritical condition is analyzed. With RNG k-εtuburlent framework, the real size choke of gas well is studied. 3. To study the sand carried by ascending flow is usually to study sandsettling as an alternative in experiment. In order to learn about the velocity ofascending sand and fluid velocity, experiment on ascending sand is done withmodel of the same size as vertical pipe in production gas well. Whenfluid-carrying sand passes the choke, its velocity is much higher. The sandy jetcomes into being and damages pipelines, spray nozzles and other accessories.Former researchers paid much effort on improving materials but withoutsignificant success. On the basis of study on velocity field at choke, a method ofremoving sand in high pressure zone to prevent gas-sand two-phase flow erosionis presented. A separation equipment is designed. 4. Most output of gas well is gas-sand two-phase flow, on which more andmore research is done. Stratified flow is a basic but complex type of two-phase V四川大学工学博士论文flow and the analytic solution is difficult to obtain, so research on this is notsufficient enough. Aiming at hydraulic features of stratified two-phase flow, flowin pipe is turned into pattern flow with rotation coordinate axis method. Analyticexpression of s...