Decrease of gas production is an indicator that liquid column is probably building up in the well and an additional energy is required to lift the liquid out should be applied to control this situation. Commonly used methods include rod pumps, gas lift, plunger lift, foaming agents, alternate flow/shut-in periods, the use of smaller diameter production tubing and swabbing.
A method has been developed to guide operations managers, engineers and technicians responsible for operations when foaming agents are chosen to provide unloading of accumulated liquid in gas and gas condensate wells.
Depending on the well conditions, surface pressure test data and field surveys data, using different foam agents (sticks and/or liquid), the suitable intermittent system can be selected. Very often the combined production system (intermittent operation combined with launching foam sticks) or only intermittent operation using motor valve or plunger lift has been chosen.
Considering that application of foaming agent essentially promotes gas lift effect to sweep the fluids out of the tubing by adjusting some input parameters, one can simulate an apparent foamed flowing gradient. To select the appropriate correction of calculated holdup factor by using any NODAL software package, the gradients comparison was used for a rough estimation of the modified flowing gradient in the typical application.
The method proposed actions necessary to start foaming agent application. Each step and parameters affecting the process efficiency have been discussed in details. Several case studies have been discussed to confirm the validity of the proposed method.
Gas and gas condensate wells accumulate liquids in the wellbore during gas production. The liquids accumulated in the well bore will cause additional hydrostatic pressure on reservoir, which results in continued reduction of available transportation energy thereby affecting the production capacity. The higher the column, the higher is the backpressure. When the liquid height creates pressure to equal the formation pressure, gas production drops to zero. A method to lift the liquid out should be applied to control this situation. Commonly used methods include rod pumps, gas lift, plunger lift, foaming agents, alternate flow/shut-in periods, the use of smaller diameter production tubing and swabbing.
Foaming agents are very simple and inexpensive means of unloading low productivity gas and gas-condensate wells. There are no downhole modifications required and the surface equipment depends on the type of treatment.
Selection of the most appropriate method for solving liquid loading problem is closely related to well behavior and data availability and prior any recommendations detailed composite system analysis (CSA) of each well was performed. The flow chart of a procedure for CSA is shown in Fig. 1. If it is necessary to simulate the well behavior assuming that liquid foam agent is injecting, the conventional system analysis has to be modified to carry the analysis. The key problem is how to simulate the changes of the flowing gradient if liquid foam agent is injection continuously through capillary tube at the bottom of the well. The capillary tube allows continuous injection of foaming agents to lighten the liquid column in the production tubing and below the packer when the conventional completion system with packer is applied.
Foaming agents provide a means to reduce the density of the liquid so that it can be removed from the well with the gas flow. The purpose of the foaming agent is to generate foam from the gas flow. Natural gas bubbling through the liquid column containing foaming agent produces foam, which helps removing liquid from the well, Fig. 2.
Low-density foam column can be lifted from the well by pressure insufficient to lift equal column of water. The foaming action decreases the hydrostatic backpressure, which increases gas production. Increased gas production further enhances the foaming action, and the well unloads.