Study On Process And Parameter Calculation Of Compound Displacement Well Killing Method

With the development of oil&gas exploration and development to deep wells,ultra-deep wells,complex reservoir to expand.The well control problems in the drilling process are also becoming increasingly complex.During the drilling of the gas wells,the mud fluid is sprayed frequently.For the case where the open hole section is long and there is no drilling tool or drill string in the downhole,it is usually considered to use the displacement method.However,the theoretical research on the displacement method is imperfect,and the construction process basically relies on the experience and lacks theoretical guidance.This is very easy to cause serious accidents such as blowout.In this paper,the compound displacement method is proposed based on the theory of gas-liquid flooding,and the calculation model of well killing parameters is established.It can calculate the maximum pumping volume of the well control fluid,the maximum gas discharge of the exhaust phase,the decay time for the well control fluid,the gas flow during the exhaust process,during each time the casing pressure and the amount of pumping volume of the well control fluid.In the thesis,the research mainly focuses on the following aspects.(1)In this paper,the well killing technology of the displacement method and bullheading killing are analyzed.Aiming at the shortcomings of the displacement method,the compound displacement method is proposed.The compound displacement method is a combination of the advantages of both the dynamic lubrication method and the displacement method.From the decay time for the well control fluid,the time of the exhaust gas,the time of the dynamic lubrication,it is reasonable to determine the killing parameters to reduce the killing time.(2)Based on the variation law of the bottomhole pressure in the process of the displacement method,the calculation formula of the maximum mud pumpage and the maximum volume of the exhaust gas is established,and the basic theory of the displacement method is improved.Consider the effect of gas density during the killing.According to the results of the example,it is shown that the main factor in the maximum volume of the well control fluid is the increase of the liquid column pressure at the early stage of well control.As the gas gradually discharges the main factor into the gas’s compressible volume.The maximum discharge volume for the exhaust phase is determined by the pressure of the liquid column,which is mainly increased by the killing fluid.The later stage of well control is determined by the inflatable volume of the gas.(3)The model of the descending velocity of the killing fluid and the critical exhaust flow model are established by the theory of liquid-carrying.And the relationship between the killing time and the exhaust flow is established.It is found that the time taken for the killing is the shortest when the exhaust speed is controlled close to the critical exhaust flow.At the same time,considering the theory of dynamic displacement method,the calculation model of dynamic displacement method is established under the influence of gas density.With the time of killing time as a bridge,the displacement method and the dynamic displacement method are combined to form the compound displacement method.Through the example,the compound displacement method can shorten the time of the killing time compared with the dynamic displacement method and the static displacement method.According to the characteristics of compound displacement method,the measures to reduce the risk of well killing are put forward.In this paper,the calculation method of each parameter is clear,which can guide for the field well operation.(4)Writing software program with MATLAB7.0 to create the compound displacement method calculation software,which is used to calculate the maximum pumping volume,the maximum exhaust volume,the optimal exhaust flow rate,the decay time for the well control fluid and the exhaust time in each stage of the killing well.It is possible to calculate the maximum pumping speed of the killing fluid during the dynamic displacement method.And can calculate the pressure and the amount of pumping fluid in the killing of the various periods of time.