Simulation And Influence Law Of Magnetorheological Temporary Plugging For Wellhead Valve Replacement

In oil and gas production,the damage of main control valve of wellhead will cause potential safety hazard and affect oil and gas production.Temporary plugging of oil and gas wellhead to replace the damaged valve is a common method to deal with such problems.However,the existing technologies of temporary plugging for valve replacement have the problems of complex construction technology and low construction efficiency.Therefore,based on the magnetorheological effect of magnetorheological material,this paper proposes and designs a kind of magnetorheological temporary plugging agent for wellhead valve replacement.Combined with the single factor experiment,the matrix of magnetorheological temporary plugging agent was optimized,and the optimal concentration range of each component was determined.Taking the compressive strength after magnetization as the index,the orthogonal experiment was designed,and a magnetorheological temporary plugging agent with good stability and high breakthrough pressure was optimized.The structure and properties of magnetorheological temporary plugging agent were characterized by infrared spectrum,X-ray diffraction,scanning electron microscope,magnetorheometer and vibrating sample magnetometer.The laboratory evaluation device and matching method of magnetorheological temporary plugging agent were designed.The plugging effect and influence law of magnetorheological temporary plugging agent were studied by experiment and numerical simulation.The results show that the optimal formulation of magnetorheological temporary plugging agent is:45%carbonyl iron powder+0.4%CH+13%acrylamide+0.08%YFJ-1+0.06%YFJ-2+0.008%NN-methylenebisacrylamide.The reaction is carried out in water bath at 30℃,and the gelation time is 20-30 min at room temperature.Magnetorheological temporary plugging agent has good soft magnetic properties and magnetic response,and its saturation magnetization decreases with the decrease of carbonyl iron powder mass concentration.Under zero field,the MRF is a shear diluted non Newtonian fluid with low initial viscosity and good injectability.When plugging the wellbore,MR temporary plugging agent is in the environment of low strain amplitude and low strain frequency,and its mechanical properties are mainly affected by extrusion force;to a certain extent,The increase of magnetic field strength and carbonyl iron powder concentration can improve its elastic modulus and compressive properties to a certain extent.The change of rheological properties of magnetorheological temporary plugging agent is closely related to the magnetization chain of magnetic particles,and the plugging strength of magnetorheological temporary plugging agent can be intelligently controlled by adjusting the magnetic field strength.Under the application of 0.5 T external magnetic field,the breakthrough pressure of magnetorheological temporary plugging agent is13.78 MPa·m^-1 in the pipe string with inner diameter of 30 mm.And the main reason of plugging failure is that the bond between the slug and the pipe wall is destroyed.The breakthrough pressure of magnetorheological temporary plugging agent increases with the increase of magnetic field,but the increasing rate slows down gradually;the breakthrough pressure increases linearly with the increase of slug length,and decreases with the increase of pipe diameter,so the slug length can be adjusted according to the plugging pressure.