Simulated Research On Early Diagenesis Of Algae Organic Matter And Its Hydrocarbon Generation Potential

The transformation from bio-organic matter into sendimentary organic matter, and its further evolution of kerogen of organic matter, is a important chain of hydrocarbon formation from oil and gas, which has significance for evaluating oil-gas area resource in widely distributed superimposed basin in China.In the early period of diagenesis, microorganism played the key role in the process of bio-organic matter transforming into geology of organic matter. Therefore, in this study, a model was built to analyze the relative microorganism’s influence on resolve, gather and storage of organic matter in the early diagenetic process which was based on the transformation of lake-based cyanobacteria and seaweed by aerobe and anaerobe. It also systematically analyzed the algae and its humification sample’s form and compositional variation. The study provided experimental evidence of geologic transformation of hydrocarbon source rock’s early burial process.In the cyanobacteria simulation experiment, the adsorption and storage function of clay minerals montmorillonite on cyanobacteria, whole procedure of cyanobacteria organic matter’s slow transforming into humus with the participation of montorillonite and final humify sample’s hydrocarbon generation experiment under thermal simulation were also studied, which also has important significance for the exploration of microorganism’s influence on algae’s hydrocarbon potential and oil-gas resource formation and evaluation, and the disciplines of Paleozoic algae matter’s hydrocarbon generation.This study explored seaweed organic matter’s form and elemental changes in solid and liquid phase during the process of transforming into pre-kerogen. The results showed that seaweed cells were gradually changed from structural intergrity into amorphous form organized by unstructured fine-particle aggregation. Besides, seaweed cells showed unstructured conditon at the beginning of anaerobism. The percentage compositions of C, H, N in seaweed shared the same variation tendency in the whole simulation process. In the aerobiotic period, because intrant aerobic micro-organism consumed organic materials in growth and metabolism, the composition of each element was decreased. However, when anaerobic period started, due to the change of seaweed structure, the percentage compositions of C, H and N were all on the rise. It illustrated that microbic funtion not only transforms seaweed’s morphological charachteristics, but also changes its elementary composition. According to change rules of content variation of ammonia nitrogen, nitric nitrogen and sulfate, the reaction time of seaweed in each stage during early diagenetic process was confirmed as follows:hydrolysis for 7 days, ammoniation for 6 days, nitration for 22 days, sulfur-oxidation for 17 days, aerobiotic stage for 45days in total, reduction of nitrate for 43 days, reduction of sulfate for 27 days and anaerobism for 70 days in total.In the laboratory simulation of the influence of varied purity of montomorillonite on microcystis aeruginosa organic matter’s gather and storage, the experimental results indicated that in hydrolysis stage cyanobacteria’s form appeared irregularity and its relation with montomorillonite was the simple mixture. However, in nitration period, the algae started to combine with montomorillonite into organic-montomorillonite compound. In addition, because of the storage function of montomorillonite on cyanobacteria organic matter, fluorescent material from the algae existed all the time, which was not completely degradation by microorganism. Montomorillonite’s special structure leads to its chemisorption by physical and chemical function so that the degradation of cyanobacteria organic matter was delayed, which is good for the storage of organic matter. Besides, the higher purity of montomorillonite existed, the more organic matter were adsorbed. From the beginning of nitration, cyanobacteria organic matter initiated resolve from macromolecule into micromolecule. The micropores in montomorillonite can adsorb methane, while the more the micropores exists, the more methane were absorbed.In the glass tube thermal simulation of fresh,7-day hydrolyzed, and the 46-day aerobiotism and 70-day anaerobism after microbiological treatment algae, the results showed that the temperature of blue-gree algae soluble organic matter’s producing peak was 250℃, and the production can reach 1.4Kg/Kg·TOC. In this thermal simulation, compared with fresh algae, mocrobial fermented samples, which had a number of soluble organic matter, had fold increased soluble organic matter production under 250℃. However, when the temperature reached 300℃, due to the thermal cracking of biological macromoleculars, the productive rate of fresh algae and mocroorganism treated algae verged to the similar stage. In the study of composition change of carbon isotopes in pyrolysis products, the results indicated that all components showed the tendency of enrichment of heavy carbon isotope with the rise of simulating temperature. Compared with fresh algae, saturated hydrocarbon in the hydrolyzed one gathered light carbon isotopes, which indicated that with the help of hydrolase when organic macromolecules resolves into micromolecules, light carbon prior gather in micromolecules. Under 250℃ in thermal simulation, aromatic hydrocarbon carbon isotopes in organic components had more significant change. While the aromatic hydrocarbon components in anaerobic treated cyanobacteria organic matter gathered light carbon isotopes. It indicated that anaerobic environment played a promoting role the increase of aromatization carbon skeleton in organic matter and the creation of heavy oil under low-temperature environment in the early stage of diagenesis.