Classification of Geological Factors in Doubtful Layer of Logging Interpretation and Overseas Case Study

Various geological influencing factors of doubtful layers are analyzed and classified according to the logging data in identifying doubtful layers of oil, gas and water. The genesis of doubtful layers is generally classified into geological genesis and engineering genesis. The geological genesis has 4 subclasses of strata, structures, reservoirs and fluids, and more than 20 tertiary subclasses. Engineering genesis can be classified into 6 factors, such as saltwater mud intrusion, well logging series selection and well testing. The characteristics of logging data of stratigraphic unconformity and its influence on logging identification of oil, gas and water in Arys oilfield in South Turgay basin are studied. The controlling factors of the faulted anticline structure Truwa in the eastern margin of the Pre-Caspian sea basin on the distribution of oil, gas and water are analyzed in detail. The geological genesis of low resistivity oil and gas layers in N oilfield in Muglad basin of Sudan and low resistivity reservoir among huge pay in Iraq are analyzed. It is difficult to identify oil, gas and water from logging data due to formation water variation in Bongor basin, Chad. After all, the relationship among porosity, resistivity and reservoir mode of doubtful layers is discussed. It is proposed that the study of doubtful layers should not only pay attention to the formation of reservoirs, but also to the patterns of oil or gas reservoirs, and should pay more attention to the seismic-well tie, so that the breakthrough of the understanding of doubtful layers in wells can play a more important role in studying reservoir distribution and providing well location suggestions.