Successful Application of Foam for Lifting Liquids from Low-Pressure Gas Wells

Abstract

Abstract Gas well loadup is a very serious problem for the petroleum industry. Gaswell loadup is the result of the loss of available reservoir energy due to the accumulation of liquids in the wellbore over time. In order to deal with this problem several techniques have been developed. They include plunger lift, small-ID tubing, gas lift, flow controllers, submersible pumps, sucker rods, swabbing, jetting and foaming. Among these foam lifting has been used quite successfully in the field for removing liquids from the wellbore and the annulus. However, there is a strong need for using a systematic approach in order to find out under which conditions foam lift is successful and under which conditions it is not successful. Foam lifting experiments are conducted in a specially designed 40'-long flow loop, in which foam is injected from the bottom of the tubing, which is filled with liquids. The efficiency of liquid removal for a wide range of gas and liquid flow rates is measured by comparing the liquid holdups at the end of each period of foam injection. The liquid removal efficiencies are also compared against cases in which no foam is injected (base-cases). Foam injection shows superior liquid removal efficiency compared to the base-cases. Special considerations are also given to cases in which a 50-psi backpressure is applied. Comparisons are also made between 1"and 2" tubing sizes. Results show that the type and concentration of the surfactants used to generate the foam has a strong influence on the liquid removal efficiency. Introduction Almost all the gas wells produce some amount of liquids. The sources of these liquids are - hydrocarbons or water condensed from the gas phase (due mainly to wellbore heat loss) and free liquids produced into the wellbore with the gas. As the gas pressure and velocity decrease with time, more and more liquids begin to accumulate near the wellbore. This accumulation can cause severe reduction to complete loss of available transport energy due to a combination of hydrostatic pressure, relative permeability, clay swelling and other effects. In order to lift liquids the gas flow rate must exceed a minimum value, known as the critical flow rate. The study of critical flow rates for continuous liquid removal from gas wells has been a popular subject of research for many years.