Abstract: In order to study water flooding effect and water flooding law of the reservoirs in Bohai SZ36-1 oilfield, coring operation was made. Coring layer with a and high degree of connectivity, loose cementation, and high water content brought difficulty to coring, so rational coring tools and drill bits were selected, mud system and wellbore configuration were optimized, reasonable construction parameters were selected, and completion of the coring operation was successful, which provided powerful first-hand information for the adjustment program for SZ36-1 oilfield and references for sealed coring operations in other oilfields in Bohai.