Geochemical Characterization Of The Impact Of Secondary Alteration On Marine Origin Oil From Northern Uplift Of The Tarim Basin

There are abundant oil and gas resources in Northern Uplift of the Tarim Basin, wherediscovered various types of oil, including normal oil, light oil, condensate oil, heavy oiland so on. The variety of oil is the result of various secondary alterations that includebiodegradation, migration fractionation, mixing, gas injection and water washing. Differentprocesses have different affect on oil component, which is important to understand thecomplexity of oil component.In this paper, geochemical analysis on25oil samples systematically is conducted,including crude oil group composition separation, gas chromatographic-mass spectrometryanalysis of saturated hydrocarbon and and aromatic hydrocarbon, combined with physicalproperty the article discussed the impacts of biodegradation, migration fractionation andmixing on oil component.The impacts of biodegradation on the physical property and component of oil havebeen studied, which geochemistry characteristics show: base lines are in bumps, n-alkanesare depleted, a large amount of25-norhopanes exist, the number of triaromatic steroids andpregnanes is relatively high. These characteristics show crude oil experiencedbiodegradation. The paper mainly studies the effect of biodegradation on various molecularcompound of crude oil, evaluates the effect of biodegradation on different reservoir withvarious geochemistry indicators.Migration fractionation is an important geochemistry alteration influencing oilphysical property and chemistry composition. Researching on migration fractionationcontributes to further study the mechanism of condensate oil. Fault-initiated pressurerelease within reservoirs and the injection of external excessive dry gas may result inoccurrence of oil and gas phases. Because of different partitioning coefficients ofcompounds in two phase flow, lower-molecular%-weight components are easier to dissolvein gas phase, yielding condensates, while higher-molecular-weight components areretained in the oil phase, yielding waxy oil cumulations. This paper discussed the influenceof various geological factors on migration fractionation and the influence of migrationfractionation on common geochemistry parameters.Within reservoir mixing is very common in this region. The early charged oil was influenced by biodegradation, which base lines are in bumps and enriches the25-norhopanes and tricycle terpane. However, the late charged is undegraded oil with fullseries of normal alkanes. Quantitative analysis of different origin oil can know thecontribution proportion of different origin oil clearly, and calculate the mixing proportionof two charged oils.According to oil present composition, the effect of biodegradation, migrationfractionation and mixing can be identified, the original state of the oil can be recovered, themigration, accumulation mechanism and process can be revealed, which can provide themore scientific basis for further exploration and exploitation.