Dynamic Regulation And Control Of Well Killing In Underbalanced Drilling

Under balanced drilling technology has the advantages of reducing reservoir damage,improving penetration rate,effectively controlling leakage and preventing differential pressure sticking.But when the underbalanced drilling meets the high pressure production layer,if it is not satisfied with the drilling operation without pressure well,the optimization design of the construction parameters in underbalanced drilling can effectively control the flow pattern and pressure of the wellbore to reduce the damage to the production layer,and fully extend the advantages of the underbalanced drilling protection reservoir.In this paper,based on the theory of wellbore gas-liquid two-phase flow and the theory of transient gas production,a set of underbalanced drilling is established,which is coupled with the calculation method of dynamic characteristic parameters,such as bottom hole pressure,gas liquid mixture density,gas production change and wellbore gas content,and the key construction parameters of underbalanced drilling.Optimization design.The main work and achievements are as follows:(1)A transient seepage calculation method for underbalanced drilling during well killing after drilling is established,and the formation gas production during well killing is calculated instantaneously.The first step:by setting the bottom hole pressure as the inner boundary condition of the partial differential equation and changing the inner boundary condition,the partial differential equation of the unsteady seepage flow in the stratum is solved numerically.The second step:to take the ring near wellbore rock infinitesimal and according to the theory of non Darcy flow and the Darcy flow,gas production for the variable pressure transient conditions.(2)A transient flow calculation method for gas well two phase well after well drilling is established.On the basis of the theory of flow pattern judgement,friction calculation and pressure gradient calculation of gas-liquid two phase steady flow,the boundary height of light and heavy slurry is coupled with the change of mud injection in the pressure well to calculate the overall situation.In the gas-liquid two-phase theory of gas production process coupled to the gas-liquid two-phase annulus formation of gas-liquid two-phase transient flow model for annular pipe flow calculation method,get the bottom pressure,different construction parameters of the formation of gas production,heavy slurry return height,wellbore density distribution,wellbore gas distribution rate of key parameters.(3)Experimental verification.According to the technological process of underbalanced drilling,the experimental flow and device are designed.The changes of key parameters such as bottom hole pressure and back height in heavy slurry are simulated in the process of underbalanced drilling,and compared with the model calculation results under the same parameters,it is proved that the proposed method can meet the requirements of engineering calculation.(4)The optimization design of the construction parameters of underbalanced drilling is carried out.Through the sensitivity analysis of the well body structure and the physical property parameters of the ST well,the optimum design of the construction parameters of the well is carried out,and the optimum combination parameters and optimum design of the mud density,pump displacement,back pressure of the wellhead are obtained.The calculation method of underbalanced drilling in this paper can optimize the construction parameters of underbalanced drilling and guide the field construction.