In oil and gas field operations, the dynamic interactions between reservoir and wellbore cannot be ignored, especially during transient flow in the near-wellbore region. As gas hydrocarbons are produced from underground reservoirs to the surface, liquids can come from condensate dropout, water break-through from the reservoir, or vapor condensation in the wellbore. In all three cases, the higher density liquid needs to be transported to the surface by the gas. If the gas phase does not provide sufficient energy to lift the liquid out of the well, the liquid will accumulate in the wellbore. The accumulation of liquid will impose an additional backpressure on the formation that can significantly affect the productivity of the well. The additional backpressure appears to result in a "U-shaped" pressure distribution along the radius in the near-wellbore region that explains the physics of the backflow scenario. However, current modeling approaches cannot capture this U-shaped pressure distribution, and the conventional pressure profile cannot explain the physics of the reinjection. In particular, current steady-state models to predict the arrival of liquid loading, diagnose its impact on production, and screen remedial options are inadequate, including Turner's criterion and Nodal Analysis. However, the dynamic interactions between the reservoir and the wellbore present a fully transient scenario, therefore none of the above solutions captures the complexity of flow transients associated with liquid loading in gas wells. The most satisfactory solution would be to couple a transient reservoir model to a transient well model, which will provide reliable predictive models to link the well dynamics with the intermittent response of a reservoir that is typical of liquid loading in gas wells. The modeling work presented here can be applied to investigate liquid loading mechanisms, and evaluate any other situation where the transient flow behavior of the near-wellbore region of the reservoir cannot be ignored, including system start-up and shut-down.

An experimental study was conducted in order to investigate the two-phase-flow phenomena in a mini-size, horizontal impacting tee junction. The test section was machined in an acrylic block with a rectangular cross-section of 1.87-mm height × 20-mm width on the inlet and outlet sides. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. The present flow-regime map was compared with several experimental maps. It is thought from those comparisons that the channel height has a more significant role in determining the flow-regime boundaries than the hydraulic diameter. The two-phase fully-developed pressure gradient was measured in the inlet and the outlet sides of the junction for six different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations. The correlations that agreed best with the present data were identified. Five single-phase test sets were performed. In each set of experiments, the pressure distribution was measured for the whole range of the mass split ratio, Wi/W1. The pressure drop at the junction at each value of Wi/W1 was calculated. Values of the pressure-loss coefficient, , were calculated at various Wi/W1 and inlet Reynolds number. The pressure-loss coefficient was strongly dependent on the inlet Reynolds number in the laminar region, while the results for the turbulent region were almost coincident. Numerical simulations of single-phase flow in an impacting tee junction of identical dimensions to that of the present test-section were performed to confirm the results of the experiments. Phase-redistribution experiments were conducted covering all four inlet flow regimes and models were proposed for predicting the experimental data. Good agreement in terms of magnitude and trend was obtained between the present experimental data and the proposed model. New correlations were developed for the single- and two-phase pressure drop in the junction.

An experimental study was conducted in order to investigate the two-phase-flow phenomena in a mini-size, horizontal impacting tee junction. The test section was machined in an acrylic block with a rectangular cross-section of 1.87-mm height × 20-mm width on the inlet and outlet sides. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. The present flow-regime map was compared with several experimental maps. It is thought from those comparisons that the channel height has a more significant role in determining the flow-regime boundaries than the hydraulic diameter. The two-phase fully-developed pressure gradient was measured in the inlet and the outlet sides of the junction for six different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations. The correlations that agreed best with the present data were identified. Five single-phase test sets were performed. In each set of experiments, the pressure distribution was measured for the whole range of the mass split ratio, Wi/W1. The pressure drop at the junction at each value of Wi/W1 was calculated. Values of the pressure-loss coefficient, , were calculated at various Wi/W1 and inlet Reynolds number. The pressure-loss coefficient was strongly dependent on the inlet Reynolds number in the laminar region, while the results for the turbulent region were almost coincident. Numerical simulations of single-phase flow in an impacting tee junction of identical dimensions to that of the present test-section were performed to confirm the results of the experiments. Phase-redistribution experiments were conducted covering all four inlet flow regimes and models were proposed for predicting the experimental data. Good agreement in terms of magnitude and trend was obtained between the present experimental data and the proposed model. New correlations were developed for the single- and two-phase pressure drop in the junction.

Phase-redistribution and full-phase separation data were generated for two-phase (air-water) flow splitting at an equal-sided impacting tee junction with a horizontal inlet and inclined outlets. The flow loop incorporated a tee junction machined in an acrylic block with the three sided having an equal diameter of 13.5 ± 0.1 mm I.D. Both sets of experiments were conducted at a nominal pressure (Ps) of 200 kPa (abs) and near-ambient temperature (Ts). The operating conditions for the phase-redistribution experiments were as follows: inlet superficial liquid velocities (JL1) ranging from 0.01 to 0.18 m/s, inlet qualities (x1) ranging from 0.1 to 0.9, mass split ratios (W3/W1) from 0 to 1.0, and outlet inclination angles ranging from horizontal to vertical. These inlet conditions corresponded to inlet flow regimes of stratified, wavy, and annular. Phase-redistribution data revealed that the redistribution of phases depended on the inlet conditions, the mass split ratio at the junction, and the inclination angle of the outlets. The magnitude of the inclination effect was dependent on the inlet flow regime. The phase redistribution in stratified flow was very sensitive to the outlet angle and full separation could be achieved at angles as low as 0.7°. Wavy flow was less sensitive to the outlet angle and annular flow was even less sensitive to the outlet angle. The capability of a single impacting tee junction to perform as a full phase separator has been examined. Experimental data were obtained for the limiting inlet conditions under which full separation was attainable at various outlet inclinations (θ) of 2.5°, 7.5°, 15°, 30°, 60°, 75°, and 90°. Full separation data have shown that a single impacting tee junction can perform as a full-phase separator for some inlet conditions. Flow phenomena near the limiting conditions were observed and a simple correlation based on the similarity between these flow phenomena and the phenomenon of liquid entrainment in small upward branches was developed. This correlation was capable of accurate prediction of the data in terms of magnitude and trend.

Phase-redistribution and full-phase separation data were generated for two-phase (air-water) flow splitting at an equal-sided impacting tee junction with a horizontal inlet and inclined outlets. The flow loop incorporated a tee junction machined in an acrylic block with the three sided having an equal diameter of 13.5 ± 0.1 mm I.D. Both sets of experiments were conducted at a nominal pressure (Ps) of 200 kPa (abs) and near-ambient temperature (Ts). The operating conditions for the phase-redistribution experiments were as follows: inlet superficial liquid velocities (JL1) ranging from 0.01 to 0.18 m/s, inlet qualities (x1) ranging from 0.1 to 0.9, mass split ratios (W3/W1) from 0 to 1.0, and outlet inclination angles ranging from horizontal to vertical. These inlet conditions corresponded to inlet flow regimes of stratified, wavy, and annular. Phase-redistribution data revealed that the redistribution of phases depended on the inlet conditions, the mass split ratio at the junction, and the inclination angle of the outlets. The magnitude of the inclination effect was dependent on the inlet flow regime. The phase redistribution in stratified flow was very sensitive to the outlet angle and full separation could be achieved at angles as low as 0.7°. Wavy flow was less sensitive to the outlet angle and annular flow was even less sensitive to the outlet angle. The capability of a single impacting tee junction to perform as a full phase separator has been examined. Experimental data were obtained for the limiting inlet conditions under which full separation was attainable at various outlet inclinations (θ) of 2.5°, 7.5°, 15°, 30°, 60°, 75°, and 90°. Full separation data have shown that a single impacting tee junction can perform as a full-phase separator for some inlet conditions. Flow phenomena near the limiting conditions were observed and a simple correlation based on the similarity between these flow phenomena and the phenomenon of liquid entrainment in small upward branches was developed. This correlation was capable of accurate prediction of the data in terms of magnitude and trend.