A very common problem of mature gas fields is liquid loading. If gas wells suffer from liquid loading production is decreased. If most or all the wells suffer from this problem, then effectively the recovery factor and reserves are reduced. Therefore engineering and operational attention is required to improve operational performance through production enhancement and optimisation.
The reason for liquid loading is liquid accumulation in the well bore due to increased liquid gas ratio (LGR) at insufficient gas production rate and gas velocity. Liquid loading is not always obvious but can be verified through the critical velocity and nodal analysis. Theoretical and field investigations deliver a wide range from 5–20 ft/sec for the minimum critical velocity for continuous removal of liquids.
There are several production enhancement techniques available to accelerate production and to prolong the effective producing life of gas wells with liquid loading problems. One method is to reduce the effective density and surface tension of the produced fluids by using surfactants as foaming agents. Foaming is an effective method because reservoir energy is utilized. But the application of surfactants to lift liquids has to fit certain gas well production conditions.
A key factor is the selection of the most effective surfactant without damaging the reservoir. The important criteria and tests for screening to determine which surfactant works best include, but are not limited to surface tension.
Depending on technical and economical limitations various methods of introducing surfactants into the well are used and several possibilities have to be taken into account. Batch or soap sticks for example are not only the simplest methods but also solutions with low initial costs. Nevertheless from a certain point automated and continuous injection should be the preferred solution as for example the installation of a capillary coiled tubing.
For managing production decline in mature gas field environments the correct application of surfactants on gas wells with liquid loading is an effective solution. Surfactants are a production optimization opportunity and can be economically used to gain incremental production from depleted gas reservoirs with liquid loading problems.