Research On Calculation Of Surge And Swab Pressures And Control Of Gas Kick In Constant Bottom Hole Managed Pressure Drilling

With the continuous development of the social economy,the current oil and gas production in the easily exploitable areas can no longer meet the increasing demand for oil and gas resources.In the process of increasing oil and gas exploration and development,drilling operations in deep and complex areas are increasing.When exploring and developing these deep and complex strata,they often face the problem of narrow “safety pressure window”,resulting in significant non-production time.Increased,it is prone to kicks,lost and lost and caused serious blowout accidents.As a more advanced drilling technology,the bottom-hole constant pressure control pressure drilling can effectively solve the problem of “narrow safety pressure window”.The prevention of gas cutting and the control of gas cutting are the core issues of pressure control drilling.The fluctuating pressure generated by the down-drilling process has become an important factor in the gas injection of the wellbore.An accurate simulation model of the updraft fluctuation pressure is established to provide the maximum safe take-off speed for the “narrow safety pressure window” formation.Firstly,the concentric annulus fluid micro-element is taken as the research object,and the momentum equation is established.According to the Herba fluid constitutive relation and the flow equal relationship,the annulus velocity distribution and the steady-state fluctuation pressure gradient expression are obtained.Aiming at the ratio of inner and outer diameters and eccentricity of various annulus,a finite-volume method based eccentric annulus fluctuation stress prediction model is proposed.The bipolar coordinate system is used to map the eccentric annulus irregular calculation domain.To the ruled rectangular calculation domain,the defect that the narrow groove approximation model must be applied to the inner and outer diameter ratios greater than 0.4 is effectively overcome.Based on the transient flow equation,considering the influence of the additional dynamic friction term,a new transient wave pressure prediction model equation is established,and the Roe algorithm is used to solve the equations.The prediction model was validated using previous field measurements.The influences of the geometry parameters of the wellbore,the rheological parameters of the drilling fluid and the movement parameters of the drilling tool on the maximum transient fluctuation pressure are analyzed.The conclusions are drawn: the drilling fluid density,the comprehensive elastic modulus of the wellbore,and the acceleration of the drilling movement.The influence of fluctuating pressure is small,and the moving speed of the drilling tool has a great influence on the transient fluctuating pressure.The degree of eccentricity affects the transient fluctuating pressure is less than the steady-state fluctuating pressure.Based on the drift flow model,the finite volume method and the Roe algorithm are used to construct the numerical flux.According to the Roe averaging rule,the linearized approximate Jacobian matrix of the coefficient matrix is obtained.The iterative format of the Roe numerical algorithm of the drift flow model is obtained.Because there is no iterative approximation operation in Roe algorithm,all discrete term operations are ordinary linear equations.Even large time steps and spatial steps can satisfy the conservation well.The gas tunnel intrusion process is divided into gas cutting detection stage and gas cutting control stage.The influence of initial wellhead back pressure,gas layer permeability,gas layer porosity,gas layer pressure and mechanical drilling speed on wellbore parameters in gas cutting detection stage is analyzed.Regularity,the conclusion that the influence of gas layer porosity is small and other parameters have great influence is obtained.Four different well control schemes for gas cutting by wellbore constant pressure method are analyzed.The wellhead back pressure is increased,gas cutting can be stopped quickly,the bottom hole constant pressure can be maintained,and the drilling fluid flow and outlet gas flow can be returned.The throttle valve is the source of pressure at the wellhead back pressure,and the wellhead back pressure is the pressure difference formed at the front and rear ends of the valve when the drilling fluid passes through the throttle valve.The position of the minimum flow area of the drilling fluid through the wedge-shaped throttle valve was found,and the minimum area was calculated,and the relationship between the spool stroke and the throttle pressure drop across the valve was derived.The effective adjustment interval of the pressure-controlled drilling wedge-shaped throttle valve is about 0.49.In this interval,the valve clearance and the throttling pressure drop function show an exponential relationship,and the pressure drop adjustment range is 0.29~14.71 MPa.