Study on Water Block in Tight Sandstone Gas Reservoirs and Solutions Thereof

The target zone of the block B in Tarim Basin is the Cretaceous Bashijiqike Formation. The depth of the wells drilled is greater than 6,000 m, and the reservoir rocks are tight, with porosity ranging from 1.0%to 9.4%, and permeability from 0.011×10^-3 to 8.56×10^-3μm². The porosity has poor relationship with permeability. The highly heterogeneous reservoir rocks have poorly developed pores, low permeability, developed fractures, high capillary forces, high clay contents, and are very easy to be affected by water blocking during well completion and fracturing. Analyses of water blocking based on the geological features of the reservoir rocks in this area indicate that the capillary water accounts for almost half of the volume of the pores, leading to highly difficult gas flow in the porous media. Using the Model SRT-II low permeability sensitivity tester, formation damage by water blocking is macroscopically analyzed through core flow experiment. Using NMR transverse relaxation time spectrum, formation damage by water blocking is microscopically analyzed. The analyses show that water blocking caused the permeability of the reservoir rocks to be reduced by 99%, and more than 90%of the water blocked in this area, mainly in the 0.01-250 nm pores. Based on the research, water blocking remover SATR0-1 and HUL were chosen and their performance studied through capillary imbibition, NMR examination, and permeability experiments. It was concluded that SATR0-1 and HUL can effectively reduce capillary forces and invasion depths by imbibition, and are helpful to liquid flowback through micro pore throats.