原油降解气的形成条件及其特征

CHARACTERISTICS OF OIL-BIODEGRADATION GAS AND THEIR DISCRIMINANT INDEX SYSTEM

原油降解气是指原油在厌氧微生物作用过程中形成的一种次生型生物气。作为非常规气藏之一,原油降解气近年来受到了极大的关注,而相关研究在我国才刚刚起步。因此,研究其生气机制及其地化特征,建立原油降解气的地球化学判识指标,并指出勘探前景,对缓解当前能源危机和原油降解气的勘探都具有重要意义。研究结果发现:原油降解气主要通过二氧化碳还原生成甲烷;中—低矿化度的NaHCO3型或CaCl2型地层水有利于微生物的繁殖及其对原油的降解进而生成甲烷。原油降解气形成的油层温度低于80℃,埋深一般小于2500m;对应原油的成熟度为低—中等成熟。原油降解气具有碳同位素轻、天然气组分干、氮气含量较高,同时含少量二氧化碳和氢气,并具有储层时代新、能大规模聚集成藏的特点。结论认为,我国具有较大的原油降解气勘探潜力。

Oil-biodegradation gas is a kind of secondary biogas generated through degradation of crude oil by anaerobic microbes.As one kind of unconventional gas pools,oil-biodegradation gas pools have drawn much attention of the industry in recent years.However,relevant researches have just been in initial stage in China.Therefore,studying the mechanism of gas generation and their geochemical features,establishing a geochemical discrimination index system,and evaluating their exploration potentials are of great significance for relieving the current energy crisis and exploration of other gases from crude oil degradation.Biodegradation of crude oil generates methane mainly through reduction of carbon dioxide.Formation water of NaHCO3 or CaCl2 types with low to medium salinity is favorable for breeding of microbes and generation of methane through biodegradation of crude oil.The biodegradation of crude oil usually occurs in reservoirs with a temperature below 80 ℃ and burial depth less than 2500 m,which corresponds to oil with low to medium maturity.Oil-biodegradation gas is characterized by light carbon isotope,dry gas component,relatively high content of nitrogen,small amount of carbon dioxide and hydrogen,young reservoirs,and large scale accumulation.It is concluded that exploration potentials of oil-biodegradation gas is relatively large in China.