Abstract: The existence of high capacity channels in unconsolidated sand stone reservoir leads to the block agent fluid leaking easily.Using low PAM and crosslinker under the condition of 80℃ generates a block agent which can be used in high capacity channel water shutoff.The block agent consists of 1.0%~3.5%PAM and 0.8%~1.4% cross linker.Through the lab experiment，the influence of PAM concentration，crosslinker concentration，temperature and formation water salinity on gel strength and gel forming time are studied.By single core flow experiment，the shut off capacity of block agent is studied.This kind of block agent which needs 8~72h to form gel，has no alternation by seal packaged in 80℃ oven after 7 months.In high capacity channels or super high permeable formations（14644×10-3靘2），the resistance coefficient is 20.8 and the gel has the strength of 27.93MPa/m and the efficiency of water shutoff access to 93.2%.It has the advantages of controllable gel forming time，high strength，well stability，and can meet the need of unconsolidated sand stone reservoir water shutoff.

Key words: unconsolidated sand stone, high capacity channel, crosslinker, water shutoff, gel