Analysis and countermeasures on decline of gas recovery with foam drainage in Sebei Gas Field

In order to explore the reasons for the decline in the effect of gas recovery with foam drainage measures in Sebei Gasfield, the tracking analysis on gas recovery effect was carried out. By using quantitative evaluation method on gas recovery effect with foam drainage, the comprehensive evaluation index on gas recovery with foam drainage was calculated, and then the index limits for well selection were determined as gas production greater than 0.3×10⁴ m³/d, water production ranging from 2 to 20 m³/d, and oil tube-casing pressure difference falling between 0.8 and 3 MPa. Most of the production parameters of on-site foam drainage wells are not within the above-mentioned index range, so the unreasonable well selection is an important reason for the decline of foam drainage effect. Furthermore, through the analysis on the adaptability between the on-site foam drainage agent and the high-salinity reservoirs, it was found that unsuitable foam drainage agent is another reason for the decline of foam drainage effect. According to the technical index limits for well selection, and by using high-salinity-resistance nano-particle foam drainage agent, 15 gas wells were selected to carry out field tests of foam drainage. As a result, the gas production and water production of these gas wells increased by an average of 9% and 31% respectively, and the pressure difference between the oil tube and casing decreased by an average of 4%. It is shown that reasonable well selection and selection of suitable foam drainage agent can effectively improve the foam drainage effect of Sebei Gasfield, providing technical support for the subsequent development of this block.