Application of the Geochemical Exploration Technique in Searching for Subtle Oil and Gas Reservoirs

To get a right knowledge of the effectiveness of the geochemical exploration technique in searching for subtle reservoirs and to summarize the successful exploration cases of such reservoir types are essential for the exploration of subtle oil and gas reservoirs at present.A subtle fault block oil reservoir in the Linnan area,Bohai Bay basin was chosen as an example,and the characteristics of the geochemical fields of both the acid-extraction methane and the heavier hydrocarbons were studied and characterized in detail by using the intensive geochemical exploration technique.The results show that both the acid-extraction methane and the heavier hydrocarbons have stable geochemical field in the study area;and the geochemical fields of the two kinds of acid-extraction hydrocarbon indicators coincide very well,both effectively indicating the underground subtle fault block oil reservoir with stable ring-like anomaly patterns.The results also show that there are causal relationship between the hydrocarbon seepage(both the microseepage and the macroseepage along Xiakou fault) from this subtle oil reservoir and the anomaly of the two acid-extraction hydrocarbon indicators.The other exploration cases from Odors basin and Junggar basin demonstrate that the fundamental base for the geochemical technique to be used effectively in exploring the subtle fault block oil reservoir is comprehensively combining various factors together,including choice of the geochemical methods,selection and combination of the effective geochemical indicators,extraction of the integrated anomaly information,and recognition of the related petroleum geological conditions.The study results of Linnan area and the geochemical exploration cases of Ordos basin and Junggar basin indicate that the geochemical exploration technique can play important roles in the exploration for subtle oil reservoirs.