The Study Of Mechnisms Of Aqeous Phase Trapping And Its Applications In Tight Sands Gas Reserviors

Tight sand gas is the most hopeful and realistic energy in 21 century, with the more and more demands of natural gas and increasing reduction of conventional gas reservoirs, more and more countries are focusing attention on tight gas by way of important back-up resource. Tight gas resource in China is rich and has huge development potential.This paper studies the tight sands gas reservoirs in Tabamiao, Northern Ordos Basin. The characters of tight gas reservoirs were mainly investigated, and abnormal low initial water saturation of this area was confirmed. Tight sands gas reservoirs, compared with conventional oil/gas reservoirs, are characteristic of low porosity, low permeability, abnormal pressure, high capillary power, and high irreducible water saturation, more natural fractures and sub-irreducible water saturation. These increase the difficulty of exportation and exploitation, the damageable characters of tight sands gas make them more difficult.Potential damage factors and mechanisms of gas reservoirs were studied by experiments, the results show that there are serious water phase trapping, serious alkali sensibility, serious acidulous sensibility, middle to serious stress sensibility in the area. It is the first time that the synthetical effects of water saturation and effective stress on effective permeability were studied, the results show that stress sensibility increases with increase of water saturation.The spontaneous imbibition method to institution water saturation is given out, it provides the guarantee for the experiments of definited water saturation stress sensitivity and spontaneous. How physical property, pore geometry, initial water saturation, interfacial tension, spontaneous imbibition mode affect spontaneous imbibition was investigated,the imbibion water and resistivity were tested, which indicate why the PiX3+2 is not detected before the application of the temporary plugging technique.Drilling and completion well fluids is introduced into tight sands gas formation under capillary-imbibition and lead to water phase trapping, which is the most significant source of impaired productivity and affects economic development of tight gas. The potential mechanisms, factors affecting severity, evaluation procedures, prevention and treatment of aqueous phase trapping were discussed, experiments point out that there is potential severity of aqueous trap in this area.At last, the necessity of using shield temporary plug-up technology is identified. The results of experiments at home and performance of oil filed prove that the prior drilling fluids is characteristic of strong severity of formation damage, and that temporary plug-up drilling fluids can reduce the invasion of solid particles and filtrates, increase production rate of gas, and accelerate appearance of high product well to some extent.