Integrated identification method for low-resistivity hydrocarbon layers in Nanpu Sag

Plenty of low-resistivity oil/gas layers exist in Nanpu sag in Bohai Bay Basin.The intense variation of lithology,physical property and water property and the deep invasion of brine mud are two key factors for sharp decrease of resistivity and reducing differences of electric characteristics of oil and water layers.Based on the logging data of mid-shallow reservoir in Nanpu sag and using the effective logging information including natural gamma and SP logging and MDT technology,this paper proposes the integrated identification method for low-resistivity reservoirs which focuses on lithology identification and uses the multi-parameter crossplot and non-logging information such as MDT and gas logging.The correspondence rate for oil and water layer interpretation by Rwa(Rt)-ΔGR,Rwa(Rt)/Rwa(SP)-ΔGR,[Rwa(Rt)/Rwa(SP)]/(1-ΔGR)-C3 crossplot is over 96%.The oil/gas layer identification is made in wells ××3,××4 and ××5 in Nanpu sag,providing the same conclusions as the formation and production test and proving the accuracy of integrated identification and assessment for low-resistivity oil/gas layers.