Annular Gas Solid Dynamic Flow In Gas Drilling Hole Enlargement Section

Gas drilling is gaining an increasing attention and application because of its high drilling rate,low cost and low damage to the reservoir.Gas drilling in the weak layer?high tectonic stress layer and so on easily lead to wellbore collapse hole enlargement.The hole enlargement will affect the distribution of the flow field within the wellbore,alter the wellbore cleaning behavior,and cause stuck drilling accidents,especially deep well gas drilling.Therefore,this paper begins the study on annular gas solid dynamic flow in gas drilling hole enlargement section.Based on mechanism of gas flow in the wellbore,particle dynamic analysis and the gas-solid two phase flow mechanism,in combination with the practical condition of gas well drilling,established a mathematical model of gas solid flow in gas well drilling hole enlargement using such methods as computational fluid dynamic simulation,numerical simulation and interior mechanism model visualization pipe rack experiment.Specific research contents and main results are as follows:(1)In combination with the practical condition of BZX gas well drilling,numerical simulation of the well,get the BZX well of flowing wellbore indicator.In the case of single gas phase,the numerical simulation method is used to analyze the dynamic distribution of annular flow field in the case of BZX well hole enlargement in different shape(different hole enlargement ratio and different hole enlargement form).(2)Based on the study of the dynamic distribution law of the annular flow field,the kinetic equation of cuttings particles was established by loading solid phase cuttings migration and analyzing force.Establishment of air-solid simulation model with hole enlargement section,by CFD simulate annular gas solid dynamic flow under the hole enlargement in different operational mode.(3)Analysis of cuttings migration and the establishment of cuttings transport model,and proposes a method of gas drilling SPP inversion of borehole enlargement rate based on the case analysis by the actual condition of BZX well,the calculation results coincide with the actual condition basically.According to the actual conditions of BZX gas wells,using CFD simulation,get different depth conditions:bottom sand thickness-borehole size?injection volume 3D chart;and analysis of different water content under the condition of downhole sand migration effect,with higher water content,sand migration is more difficult.(4)Visual experimental aircraft of the gas drilling cuttings migration in hole enlargement section is developed independently.Visual laboratory experiments on cuttings migration are conducted.It is obtained that the interface injection volume of the cuttings dynamic floating debris particles in the hole enlargement section and the interface injection volume when the bottom hole sand thickness is 0.1m.(5)Study on the law of annulus cuttings carrying in BZX well hole enlargement section.Based on the numerical simulation,the maximum diameter of the gas carrying cuttings is obtained under different injection volume conditions,and provides the recommended parameters,thus providing guidance for the gas drilling operation.This paper provides theoretical guidance for inject parameter design of gas drilling and the improvement of drilling risk control process.