Laboratory Study On Liquid Lock Damage Of Low - Permeability Condensate Gas Reservoirs

During the exploitation of the condensate gas reservoir, a lot of water-based working fluid flow into the reservoir on a series of operation such as fracturing, acidization, workover and so on. If the working fluid cannot flowback timely, the liquid phase will accumulate in porous media. The accumulated liquid will cause the water lock, which results in the reduction of the gas well production. Moreover, during the production of the condensate gas reservoir, the condensate will occur when the pressure drops below the dew point pressure. Condensate gas will condense into liquid condensate oil, which adsorbed on the surface of rock, and it will lead to the decrease of gas permeability. Especially for the low permeability gas reservoir, it is easy to compact the rock structure and decrease the pore throat radius. In fact it will be more difficult to remove the liquid lock. Thus, it is of great significance to remove the water lock and condensate effect for the condensate reservoir.In this paper, removal of liquid lock for Yaha low permeability condensate gas reservoir of Tarim oilfield are studied on laboratory test, based on the summary of the liquid lock damage mechanism and the liquid lock damage removalte chnology in the domestic and abroad, surface tension and interfacial tension of the surfactants act as evaluation index the lowest values will be used for removal liquid lock damage. The final formula is:0.06%TF3721of fluorine surfactant+0.2%HB of sulfonate Gemini surfactant and0.08%TF280of fluorine surfactant+0.2%HB of sulfonate Gemini surfactant. Self-imbibition ability and core flow experiments are conducted. The results show that this surfactant system can clean-up the water lock effectively, but it cannot clean the condensate oil. In contrast, the method of methanol with gas can clean up the condensate oil, but it will cause the salting-out effect for high salinity reservoir and lock the stratum, this phenomenon emerge gradually in latter development of oilfield production. Therefore it is greatly challenge to clean-up the condensate oil damage for high salinity reservoir such as Yaha.A new technology method is proposed on the basis of analyzing the liquid lock damage mechanism deeply. The capillary test is done as premier experimentation, result shows that this new technology change surface properties of the rock effectively. Using silicon dioxide as solation to treat with the low permeability core under high temperatures, the roughness of rock surface and inside surface of porous medium has increased, as is by SEM. Then, the cores are treated by TF3721, the fluorine surfactant can be absorbed sufficient on rock surface and inside surface of porous medium, hydrophobic and oleophobic properties of the rock increase.A series of experiment, including energy spectrum analysis、wetting angle experiment and spontaneous imbibition experiment for the natural sandstone core are studied. By energy spectrum analysis, the content of fluoride is55.82%and the content of silicon is44.18%in surface of the rock after the treatment of silicon dioxide and TF3721, it shows that the fluorine alkyl of TF3721has combined with the rock surface and porous medium. By the spontaneous imbibition experiment, it shows that strong water wettability has turned to gas-wetting in water/gas system and the strong oil wettability has turned to weak oil wettability or intermediate-wet. With the treatment, the result of wetting angle experiment shows that the oil/gas contact angle has changed from44.5°to120.5°and the water/gas wetting angle has changed from35.2°to122.5°. The rock surface appears wettability reversal, it has hydrophobic and oleophobic properties. The core displacement experiment shows that recovery rate of gas permeability can reach87.5%for the water lock damage and89.1%for the condensate oil damage.This new technology and method can reduce the absorption of liquid in porous medium, drop the capillary resistance, therefore, it can remove the liquid lock damage of the low permeability gas condensate reservoir.