Prevention and Control of Gas Hydrates for Foam Combination Flooding

摘要

Foam combination flooding is one of the most capable tertiaryrnoil recovery techniques. For the pilot test of foam combinationrnflooding performed in Sa-Nan, Daqing, gas hydrates affect thernnormal gas injection badly. The designed gas injection is 182rndays, however, due to the influence of gas hydrates, only 59rndays of gas injection is conducted. The injected gas is justrnabout 36 days’ work in the design. Based on the pilot test inrnSa-Nan, this paper elucidates the structure, phase state andrnforming condition of gas hydrates and proposes a number ofrneffective measures to prevent and remove the formation of gasrnhydrates in the process of foam combination flooding. Twornmodels for predicting the forming condition of gas hydratesrnfor foam combination flooding are presented in this paper.rnPhase-equilibrium-constant method is proved to be morernaccurate and reliable than empirical graphic method and isrnrecommended for use in research work and field practice torndetermine the forming condition of gas hydrates in foamrncombination flooding. With this method, the formingrncondition of gas hydrates in Sa-Nan pilot is calculated. Thernresult shows that gas hydrates will generate at temperaturernlower than 73.4°F. Three ways are proved effective to preventrnthe formation of gas hydrates for foam combination flooding,rnwhich are reducing the water content of natural gas, improvingrnthe injection technology to avoid the contact of water with gasrnand adding certain suitable inhibiting agent. Heating, loweringrnpressure and adding deicing agent are suggested as the threerngood measures to get rid of the plugging in injection pipelinesrncaused by gas hydrates for foam combination flooding.