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In the process of thermal recovery of heavy oil, the energy exchanges with its surrounding environment during steam migration in a tube, so as to heat will be lost and the steam enthalpy will decrease gradually. It will seriously affect the steam-simulation effect of heavy oil wells if string structure, horizontal section length, steam injection volume, and steam dryness are not reasonably designed. Therefore, the accurate calculation and forecast of thermodynamic parameters of steam along the wellbore, such as pressure, temperature, and dryness, is the key to evaluate the gas injection effect. It also has great significance for the optimization of steam-simulated parameters. In this paper, a dynamic model for calculating thermal parameters in horizontal wells with steam huff and puff is established based on one-dimensional unsteady heat-transfer theory, in which the characteristics of the variable mass flow in the horizontal segment is considered. The results shows that the maximum relative error between the calculation results and the measured data is less than 5%, which proves the accuracy of the model. The effect of wellhead steam parameters on the distribution of steam thermodynamic parameters in horizontal wellbore is almost consistent. The steam-injection rate is in direct proportion to the horizontal wellbore extension distance. In addition, the influence of steam-injection time on steam temperature, pressure, and dryness can be ignored. [ABSTRACT FROM AUTHOR]

In this article, a more-general flow-pattern classification of oil/water two-phase flow in the horizontal wellbore is proposed first according to the theoretical analysis and previous research achievements, on the basis of which a simplification is then performed through reasonable incorporation, and the ultimate flow patterns considered for modeling are reduced to two categories containing only six standard patterns. By use of the classical twofluid and homogeneous modeling methodologies stemming from oil/water two-phase flow in conventional pipes, combined with the simplified classification, a mechanistic model is developed to predict the flow characteristics including the flow patterns and pressure losses for oil/water two-phase variable-mass flow in the horizontal wellbore. Model implementation is performed on the basis of the universal principle that a system will stabilize to the equilibrium state of minimum energy. Overall performance of the mechanistic model is then validated against the new data sets measured upon a large-scale experimental apparatus at the China University of Petroleum (CUP), which is designed and constructed to simulate the gas/oil/water multiphase flow in horizontal wellbores with wall mass transfer. Results show that the model developed in this paper can not only properly predict the flow patterns of oil/water two-phase flow in the horizontal wellbore, but also has high prediction accuracy for the pressure drops. Compared with the new experimental data for oil/water two-phase variable-mass flow that covers a series of input water-volumetric fractions ranging from 10 to 90%, the highest absolute average percentage error of the new unified model is 12% and the whole error is 9.2%, which demonstrates an acceptable performance. Investigations conducted in this study further enrich and develop the theory of hydrodynamic calculation for oil/water flow in the horizontal wellbore with wall influx. [ABSTRACT FROM AUTHOR]