Gas-liquid two-phase flow exists extensively in the transportation of hydrocarbon fluids. A more precise prediction of liquid holdup in near-horizontal, wet-gas pipelines is needed in order to better predict pressure drop and size downstream processing facilities. The most important parameters are pipe geometry (pipe diameter and orientation), physical properties of the gas and liquid (density, viscosity and surface tension) and flow conditions (velocity, temperature and pressure). Stratified flow and annular flow are the two flow patterns observed most often in near-horizontal pipelines under low liquid loading conditions. Low liquid loading is commonly referred to as cases in which liquid loading is less than 1,100 m 3 /MMm 3 (200 bbl/MMscf). A previous study by Meng [1] was carried out on a new low liquid loading flow loop. A transparent test section (50.8-mm inner diameter and 19-m long) could be inclined within ± 2° from the horizontal. Mineral oil was used as the liquid and air was used as the gas phase. A surprising phenomenon was observed with air-oil flow; at high gas velocities (annular flow), liquid film flow rate, liquid holdup and pressure gradient decreased as liquid velocity increased. Low liquid loading gas-liquid two-phase flow in near-horizontal pipes was studied for air-water flow in the present study, in order to investigate the effects of the liquid properties on flow characteristics. This study was carried out on the same 2-in. ID flow loop used by Meng. The measured parameters included gas flow rate, liquid flow rate, pressure, differential pressure, temperature, liquid holdup, pipe wetted perimeter, liquid film flow rate, droplet entrainment fraction and droplet deposition rate. A new phenomenon was observed with air-water flow at low superficial velocities and with a liquid loading larger than 600 m 3 /MMm 3 . The liquid holdup increased as gas superficial velocity increased.

The effects of buoyancy on the flow regimes of submerged gas injection were studied in this investigation. A capillary tube submerged in water was used for gas injection in microgravity and terrestrial conditions, and the resulting flow regimes and bubble sizes were documented. The effects of liquid co-flow and reduced surface tension were also analyzed. Under reduced gravity, three flow regimes were observed over the range of conditions tested. At low gas flow rates, the bubbles did not detach from the injector, forming an interconnected bubble cluster that adhered to the injector. Single bubbles started detaching and moving away from the injector when the Weber number reached a value around 3. At gas flow rates corresponding to a Weber number value of 10, the bubble coalescence regime was observed near the injector. It was found that the absence of buoyancy prevented the formation of the jetting regime. For all gas throughputs, the co-flowing liquid aided the detachment of the bubbles, resulting in the generation of more uniform bubbles than in quiescent liquids. The presence of co-flow resulted in a smaller bubble size accompanied by an increased frequency of bubble formation. Reduced surface tension produced a similar effect, resulting in smaller bubbles.

The engineering applications of spreading and adhesion phenomena involving fluids on solids are numerous. The adhesive and spreading interactions at the solid-fluid interfaces are well characterized by dynamic contact angles. This study reports on the results of an experimental investigation into the effect of solid surface roughness on dynamic contact angles in solid-liquid-liquid (S-L-L) systems. The experiment involved the use of Wilhelmy Plate apparatus to measure adhesion tension (which is the product of interfacial tension and cosine of the contact angle between the liquid-liquid interface and the solid surface), the DuNuoy tensiometer to measure the liquid-liquid interfacial tension, and a profilometer to characterize the roughness of the solid surfaces used. The components of the solid-liquid-liquid systems studied consisted of: (i) smooth glass, roughened quartz and an actual rock surface for the solid phase, (ii) normal-hexane and deionized water as the two immiscible liquid phases. The dynamic contact angles (advancing and receding angles) of the three-phase (rock-oil-water) system provide essential information about the wettability of petroleum resrvoirs. The wettability of a reservoir is an important parameter that affects oil recovery in primary, secondary, and enhanced recovery operations [1]. Contact angle measurements on smooth surfaces are generally used to characterize reservoir wettability. However pore surfaces within reservoir rocks are essentially rough and hence it is important to determine the effect of such roughness on measured contact angles. There is very little information in the open literature on the effect of surface roughness on dynamic contact angles in S-L-L systems. In the present work, four levels of roughness of solid surfaces of similar mineralogy (quartz and glass) were tested in hexane-deionized water fluid pair. The advancing and receding contact angles measured at ambient conditions were analyzed for wettability effects. It was found that as surface roughness increased, the dynamic contact angles also increased. The wettability of the rock-oil-water system shifted from weakly water-wet for the smooth glass to intermediate-wet for the roughened surface. The general trends observed in our study were found to be in good agreement with other published results. However, the generally held notion of increasing contact angle hysteresis with increasing roughness appears to be incorrect in solid-liquid-liquid systems.