Abstract
Gas production can be enhanced by the unloading of liquid accumulated in the wellbore. These liquids can be either formation water or gas condensate. Conventionally, liquid loading is addressed by dropping soap sticks into gas well or nitrogen lifting operation without foaming. During this process, achieving a stable foam with condensate is a challenging task. In this paper, an advanced foaming system was developed to unload both formation water and condensate in addition to nitrogen lifting.
The novel foaming system consists of aqueous and hydrocarbon soluble foaming agents. The aqueous foaming agent is an amphoteric surfactant, whereas the hydrocarbon based foaming agent is a fluoro-polymeric surfactant. The test fluid was prepared by mixing foaming agent with synthetically prepared formation water and a condensate sample separately. The foamability of surfactants was assessed by using a static foam analyzer, measuring foam half-life. Liquid unloading phenomena was investigated using an in-house developed column flow test. Foam rheometer was used to measure stability under high-pressure high-temperature (HPHT) conditions.
The stability of foam greatly depends on ideal hydrophilic-lipophillic balance (HLB). This balance can be achieved by optimizing the foaming agents which significantly rely on liquid drainage, gas diffusion, and foam rupturing at high temperature. The aqueous foaming agent was analyzed from 0.5 to 1% (vol) using synthetically prepared formation water, whereas the hydrocarbon based foaming agent was optimized to 0.5% (vol) using actual condensate samples. The column flow test, which measures liquid unloading characteristics, was conducted to ensure liquid unloading from the glass column. Nitrogen gas was purged in the column from the bottom with 200 to 400 ml/min and the rate of foam displacement was measured. The stability of the foam prepared using an aqueous foaming agent with formation water was analyzed by foam viscosity at various qualities using N2 gas at different shear rate form 100-500 1/s at 1500 psi and 300°F. The effect pressure on foam viscosity was also studied to assess foam stability under HPHT conditions.
Liquid unloading using soap sticks is limited to liquids accumulated with aqueous fluids. In this paper, the advanced foaming system addresses both aqueous and hydrocarbon liquids accumulated in the wellbore that can be applicable for high temperature wells. These foaming systems can be injected with N2 with coiled tubing operation.
