砂岩储层中原油微生物降解的模拟实验研究

Simulated Experiment Research on Oil Biodegradation in Sand Reservoir

模拟辽河冷东—雷家地区的砂砾岩储层条件，采用该地区的正常原油，在３０℃恒温和充氧下以及有营养元素的水溶液中，进行了原油喜氧微生物降解实验。实验表明，经微生物降解后，原油的化学组成发生了较大变化，饱和烃含量下降，沥青质、非烃含量上升；水溶液的ｐＨ值下降，并在其中检测出了有机酸，可见在微生物的代谢过程中，原油中的烃类分子被部分转化为水溶性含氧酸性产物。降解实验的油样与取自同一地区的两个重质原油饱和烃气相色谱图比较，两者在组成上极其相近，其结果说明辽河油田的重油成因，是原油遭受了喜氧微生物的降解。实验对微生物降解过程的动力学进行了初步研究。微生物对饱和烃馏分中不同化合物的降解序列为：短链正构烷烃、长链正构烷烃、异构烷烃、环状烷烃。但当各组分间的浓度发生较大变化时。

Heavy oils are widely distributed in many oil and gas fields. Most of them are shallow reservoirs. One of the heavy oil origins is aerobic biodegradation, a major process which affected crude oil in reservoirs. In this paper the experiment of crude oil aerobic biodegradation has been carried out under 30℃ constant temperature and in aqueous solution containing nutritional elements by simulating sand and gravel reservoir condition in Lengdong Leija zone,Liaohe Oil Field. The regular oils used for experimental samples were taken from the zone. The results show that the chemical compositions of oil samples have been changed considerably after biodegradation, in which the contents of saturated hydrocarbons group decreaseds but both the contents of asphalt group and non hydrocarbons group increase. In GC graphs of saturated hydrocarbons in oil samples, n alkanes decrease gradually with experimental days to almost disappeared. The feature absorbed peaks of alkanes in IR graphs weakens but that of oxygen containing polarradicals strengthens. Comparation between the oil samples underg one 60 days biodegradation with two heavy oils taken from the same zone, their of groups and GC graphs of saturated hydrocarbons are very similar, which indicates that one of the origins of heavy oils in Liaohe oil field was the result of oil biodegradation. This deduction is in accordance with the geologic background of shallow reservoir in Liaohe in which fresh water was injected and formation water moved actively. As for aqueous solutions, the pH values decreases and several organic acids have been detected in them with isotachophoresis (ITP). These show that hydrocarbons in oil were partially changed into some soluble acidity substances containing oxygen atoms during the metabolism of bacteria. It is notable that the soluble acidity substances could react with minerals in sand reservoir in formation water media under lower pH values,so the property of reservoir altered, which is helpful foryexplaining the phenomenon of sand stone becoming loose in reservoir. Furthermore, the kinetics of biodegradation is probed preliminarly through the experiment. The order of biodegradation on different compounds in saturated hydrocarbons is known to be: Short Chain n alkanes>Long Chain n alkanes>i alkanes>cyclealkanes. But when the concentrations of the compounds change greatly, the order will be reversed.