Numerical Simulation Research on Transient Thermal-Fluid-Chemical Coupling of Abandoned Wellbore

In the process of plugging wellbore with balanced plugging mud, hydration reaction kinetics, heat transfer and fluid mechanics interact with each other during the cement plugging stage, forming a complex physical and chemical process, which has not been fully taken into account in the current mechanical model of abandoned wellbore. Based on this, firstly, considering the hydration of cement plug during solidification stage, a transient heat-fluid-chemical coupling model of the abandoned wellbore is established. Then, the implicit finite difference method is used to discretized solve the simultaneous equations, and the characteristics of temperature distribution, hydration law of cement plug and pressure distribution of the abandoned wellbore are analyzed. The results show that the temperature of deep cement plug is almost constant after reaching the peak value under the coupling effect of thermal-fluid-chemical interaction, the temperature of shallow cement plug decreased significantly (by about 8 ℃) and the middle cement plug was followed by a reduction of about 5 ℃. The porosity and pore pressure of deep cement plug decreased rapidly, followed by the middle cement plug, and the shallow cement plug was the slowest. The hydration degree, gel strength and chemical shrinkage rate of the deep cement plug increased rapidly, followed by the middle cement plug, and the shallow cement plug was relatively slow.