Production of fluids from low-pressure reservoirs requires a continuous or an intermittent artificial lifting technology. If the shut-in fluid level is less than 20% of the depth of the well finding a suitable and economic artificial lifting technology is a challenging task. Depending on local conditions and economics, gas or steam lifting alone or associated with other artificial lifting technologies is selected.
Within a limited range of gas-liquid flowrates, use of smalldiameter gas lifting technology is better suited than the gas lifting using conventional tubing to produce liquids from lowpressure reservoirs.
Laboratory investigations dedicated to small-diameter gas lifting operations have been so far limited to fluid transfer operations requiring maximum 10–20 m. This study responds to the industry need for a better evaluation of depth - diameter flowrates limitations in view of assessing the potential field application of gas lifting for very low reservoir pressures and relatively small liquid flowrates.
Production of oil and gas from pressure-depleted reservoirs, recovery of methane from coalbed reserves, and efficient drainage of heavy oil and saturated high-temperature condensate produced under steam-assisted gravity methods, where reservoir pressure is marginally low, require a revisiting of conventional artificial lifting technologies. For example, there are thousands of dormant gas wells where bottom water aquifers of 50 m or less impede gas production. Similar conditions are often found in the coalbed methane reservoirs. Use of submersible electric pumps for lowpressure, low liquid production reservoirs is rarely an economic or a viable technical option.
The availability of gas and the relatively small amount of liquid to be transferred suggest gas lifting as a potential strategy for producing the reservoir water and releasing the gas. However, conventional gas lifting (using tubes with a diameter D>1 in.) is not possible due to the extreme low reservoir pressure conditions. Small diameter pipes (D<1 in.) were occasionally used for gas lifting operations in such fields with mixed results.
In this paper, a critical review of the existing literature on the numerical evaluation methods of gas lifting was presented first. Laboratory tests were conducted by using a specially designed rig and the results were used to evaluate the accuracy of the existing model predictions. Experimental results were also used for assessing the effect of gas-liquid flowrate and interfacial tension on the liquid production rate and flowing bottomhole pressure.
Experimental data were further used for developing a model to determine critical limit of the small diameter gas lifting technique under field conditions. The new model, better adapted for the needs of the industry, can be used to transfer laboratory information to the field scale.
Gaslifting or airlift has been used to remove water from flooded mines since 17821–2. Today, natural gaslifting is commonly used for oil wells where gas and liquid are produced together. Conventional gaslifting uses tubing (or ducts) with a diameter greater than 1 in. Vertical upward transport of gas and liquid for such conditions is well investigated and both empirical3 and mechanistic models are available.4–6
