平推压井法排量优化新模型及泵压分析

A New Optimization Model of Bullheading Killing Displacement and Analysis of Well Kill Curve

目前平推法压井井筒压力按照单相流计算,计算结果不准确,造成现场压井施工的盲目性。文章考虑井底压力差、温度、渗透率等因素,建立了压井液排量优化新模型,新模型计算结果与现场实测泵注压力最大峰值误差为7.119%。通过对模型计算分析,得到了排量、渗透率、压井液密度对平推法压井井筒压力的影响,绘制了平推法压井因素影响图。结果表明:(1)随压井液密度及排量的增大,泵注压力呈现先增大后减小趋势;排量增大压井时间缩短,存在高套压反弹风险;(2)压井第一阶段(t≤15 min)井底有效压力主要受摩擦阻力的影响,压井第二阶段(t>15 min),井底有效压力主要是受静液柱压力影响;(3)随地层渗透率增大,井口泵注压力呈现减小趋势;压井施工排量对井底压差影响较大,压井排量800 L/min同1000 L/min比较,井底压差从2.06 MPa升至8.22 MPa;(4)对于超低渗地层,如果采取大排量平推法压井可能面临井筒压力过大引发管柱及地层破裂的风险,地层渗透率越大对平推法越有利;该模型对压井施工单制定和压井作业具有指导作用。

At present,the wellbore pressure is calculated according to single-phase flow while using bullheading method of wellcontrol,and the calculation result is not accurate,resulting in the blindness of the well killing operation on site.Considering bottomhole pressure difference,temperature,permeability and other factors,a new model was established to optimize the displacement of kill fluid in this paper.The maximum error between the calculation results of the new model and the field measured pumping pressure was 7.119%.Through the calculation and analysis of the model,the influence of displacement,permeability and kill fluid density on the wellbore pressure of the bullheading method was obtained,and the influence diagram of the factors of bullheading method was drawn.The results show that:(1)with the increase of kill fluid density and displacement,the pumping pressure increases first and then decreases;with the increase of discharge rate,the killing time is shortened,and there is the risk of high casing pressure rebound.(2)the bottom hole effective pressure in the first stage of well killing(t≤15 min)is mainly affected by friction resistance,and the bottom hole effective pressure in the second stage of well killing(t>15 min)is mainly affected by hydrostatic column pressure;(3)with the increase of formation permeability,wellhead pump injection pressure shows a decreasing trend;compared with 1000 L/min and 800 L/min,the bottom hole pressure difference increases from 2.06 MPa to 8.22 MPa.(4)for the ultralow permeability formation,if the well kill method with large displacement is adopted,it may face the risk of pipe string and formation rupture caused by excessive wellbore pressure.The greater the formation permeability,the more favorable the hullheading method,which plays an important effect on the formulation of operating plan and its operation.