| The deep oil and gas resource is an important domain of the oil and gas exploration and development in China. In especial, the deep marine oil and gas reservoir is provided with the complex geological conditions, the development of fracture and cave, the high pressure and production, and the narrow safe window. Thus, the exchange of mass between the wellbore and formation occurs likely, and leads to leakage, overflow, existence of leakage and overflow at the same time during drilling. Then the complex multiphase flow occurs in wellbore. In order to accurately control the wellbore pressure, the law of complex multiphase flow and the dynamic response characteristics of the flow parameters of phases should be required study for various working conditions. The process of multiphase flow formed because of formation fluid influx is transient flow. The numerical simulation is an important method for studying the transient flow of complex multiphase in wellbore. The accurate numerical simulation of complex multiphase flow in wellbore under the condition of the gas flow rate continuous variation demands the numerical algorithm with high precision, stability and resolution. Moreover, the numerical algorithm should capture the discontinuities accurately in the flow field. Recently, the domestic researches mainly focus on well killing process on the base of constant gas influx rate. The traditional numerical algorithms used in the researches are not validated by classical numerical test cases. The calculation precision of each phase mass flow rate at different locations is also not validated, but it is an important effect on the numerical simulation.In this paper, the research focuses on the method of accurate numerical calculation of the transient flow of complex multiphase in wellbore. The main research is as follows:(1) Considering the temperature of wellbore, based on the Shi slip relation and other submodels, a general and simple drift flux model is presented for dynamic gas-liquid two-phase flow of well coupled with reservoir. The model is used for analysis of the law of complex multiphase flow and the dynamic response characteristics of the flow parameters of phases by numerical simulation.(2) The AUSM (Advection Upstream Splitting Method) family schemes, which are independent of the (approximate) Riemann solver or Jacobian matrix, have the advantages of simple form and small amount of calculation. Numerical calculation method of second order accurate in time and space is obtained by using the classical Runge-Kutta method and monotonous MUSCL (Monotone Upstream-Centred Schemes for Conservation Laws) technique with van Leer limiter.(3) The comparisons between the results of classical numerical test cases by AUSMV and the reference show fair agreement. The study indicates that AUSMV scheme has low dissipation effect and dispersion effect, no obvious numerical oscillation. The discontinuous is not pulled wide or smoothed. Moreover, the second order AUSMV scheme has better ability of capturing discontinuous than the first order AUSMV scheme, and has the advantages of small amount of calculation, high precision, high resolution and high stability.(4) A laboratory experiment is implemented to simulate the process of continuous gas influx. The pressures at different depths of the test section of the annular tube are measured, and the change of the flow behavior is observed during the experiment. The error of the simulation results between the laboratory experiment and full-scale experiment is approximately ±10% and ±5%, respectively. The calculation accuracy can meet the engineering needs.(5) The working conditions of constant gas influx rate, continuous variation of gas influx rate, one blast of gas influx, intermittent gas influx, drilling through thin and thick reservoir are studied by numerical simulation using the second order AUSMV scheme. Then, the analysis of the law of complex multiphase flow and dynamic response characteristics of flow parameters of phases in wellbore is implemented. |
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