Application of NDW clay-free low damage drilling fluid on Well CB8-3

Changbei gasfield belongs to tight gas reservoir.In the drilling process,the invasion of drilling fluids is one of the main reservoir damage factors.To reduce the invasion of drilling and completion fluids,studies were mainly focus on temporary plugging and wettability change of reservoir rock surface,and a type of NDW clay-free low damage drilling fluid was developed.The fluid had effective protection for gas reservoir because its average damage ratio to the pay-zone is only 11.25%,tested under reservoir conditions.The fliud had good temporary plugging,excellent inhibitive ability and high lubricity.In the whole drilling of horizontal interval in well CB8-3,the cumulative horizontal interval length using the fluid is 4 388 m,and the borehole is always kept clean,with no blockage and no pipe-sticking during tripping,and no sand setting in downhole.Moreover,more than 240 m shale was stable and the production of 230×104m3/d in this well was obtained,which created the new record of highest individual production rate in onshore low permeability gasfield in China.