Study On The Dynamic Characteristics Of Bottom Hole Pressure Of Killing Well In Empty Hole

In the process of oil and gas drilling,unreasonable drilling program or misoperation can cause overflow.Delayed or failed control may cause empty well condition that drilling string is at the bottom and drilling fluid is out of the well.In the well killing process,the inaccurate parameters selection or improper control measure can lead to blowout out.However,well killing parameters and the well killing technology are determined by experience,so the success rate of well killing is often not high.Therefore,it is necessary to study the dynamic characteristics of bottom hole pressure and the control method of bottom hole pressure in the process of well killing.Then,it can provide guidance for the air well killing process measures,and improve the success rate of wells.Based on the well control theory,filtration theory and multiphase flow theory,through the establishment of well killing physical model,this thesis derived the mathematical model of the different stages of bottom hole pressure,and the model of relative parameters of well killing,according to previous experiment.This thesis then analyzed the influence of wellhead casing pressure on bottom hole pressure and gas invasion before the killing mud enters the annulus,and studied the influence of well killing parameters(discharge rate,density,casing pressure)on the bottom hole pressure,gas invasion and liquid column height of gas-liquid two-phase mixture after entering the annulus;On the basis of theoretical analysis,put forward the wellhead casing pressure after the first stand pipe pressure of bottom hole pressure control method.Based on the analysis of bottom pressure and gas invasion,the thesis put forward two well killing methods for empty well:water before the normal density of well killing fluid method and heavy density before normal density of well killing fluid method.And then research the bottom hole pressure under the two methods respectively,compare the application conditions,advantages and disadvantages of the two well killing methods.Finally,according to the mathematical model of bottom hole pressure,the software is compiled.The simulation results show that before the killing mud enters the annulus,the greater the casing pressure is,the greater the bottom hole pressure is,and the less the gas production is,the more beneficial to the later well killing.After the killing mud enters the annulus,the higher liquid density,the bigger kill rate and the higher casing pressure will bring higher bottom hole pressure,less gas invasion,and easier to well killing.Under the same conditions,the greater casing pressure,the higher liquid density,the longer the gas liquid mixture reaches the wellhead,and the more fluid pumped into the well,the more beneficial to the well killing.Before the bottom pressure balances formation pressure,in order to balance the formation pressure as soon as possible,it should be adjusted by the throttle valve to maintain wellhead pressure at large values(analysis),the best for the maximum allowable wellhead pressure;After the bottom pressure balances the formation pressure,it should be adjusted by the throttle valve to control the pressure of vertical pipe and maintain wellbore pressure balance.For the method of normal density killing fluid after water,although the bottom hole pressure is difficult to balance formation pressure,but it can increase initial pressure before the normal density fluid into the annular,which not only won the allocation of killing fluid,but also saves the amount of fluid;When it is equipped with high-density well killing fluid,the method of well killing fluid after heavy fluid can save well killing fluid for balancing the formation pressure.But when the well killing fluid is not in the annulus,the stand pipe pressure decreases greatly due to the lower bottom hole pressure.Finally,combined with the characteristics of empty well killing,the measures of empty well killing are put forward.The calculation model not only can be used to predict the change regulation of bottom hole pressure under different pressure parameters,but also can guide the control of the bottom pressure in the process of well killing,which provides a theoretical basis for success well killing.