The damage evaluating techniques of the tight sandstone gas reservoirs

With the characteristics of small throat,fractured and ultra-low initial water saturation,the tight sandstone gas reservoirs are likely to be damaged during the exploration and exploitation,the water blocking and stress sensitivity are the most fatal damage types. spontaneous imbibition-centrifuge,dpt index method and self-made experimental device were used to qualitatively and quantitatively evaluate water blocking damage degree under overbalance and underbalance condition. the stress sensitivity of tight sandstone gas reservoirs is evaluated by capillary flow porometer. the results indicate that tight sandstone gas reservoirs have strong water blocking damage potentiality; even in underbalanced condition the water countercurrent imbibition can decrease the tight sandstone gas reservoirs permeability in some degree,the lower negative pressure differential cannot protect reservoir effectively during water-based underbalanced drilling. with the increase of effective stress,the pore size distribution of matrix mobile to small size,the fractures permeability decrease obviously; during the beginning of stress loading the fracture closed largely,the later stage the closing degree become slightly. during water-based underbalanced drilling,superimposed effect of water blocking and stress sensitivity increase the reservoir damage degree. the simulations of real in-situ reservoir condition,combining the laboratory evaluating results and engineering design closely are the emphasis of the next research work. © 2014 pakistan journal of statistics.