塔里木盆地塔河油田奥陶系原油及族组分碳同位素倒转成因分析

深入剖析塔河油田奥陶系原油与族组成的碳同位素倒转机理对于成藏演化认识和油气勘探均具有重要意义。对93件奥陶系原油及族组分在平面上与深度上的碳同位素变化特征分析表明：倒转程度在平面上由东向西逐渐加深，具有较好的规律性，艾丁地区、塔河主体区、托普台地区△δ¹³C_{沥青质-非烃}值分别为-0.73‰、-0.63‰、-0.58‰，在塔河9区及周边地区与南部盐下地区为正值。艾丁地区和塔河主体区的部分井原油δ¹³C_饱和烃与δ¹³C_全油发生了倒转；δ¹³C_沥青质与其他组分碳同位素及δ¹³C_全油在塔河油田不同区域发生了不同程度的倒转；而在深度上倒转分布与原油的埋藏深度缺乏相关性，由埋藏深度引起的热力作用不是造成塔河油田奥陶系原油族组分中沥青质碳同位素与其他组分碳同位素倒转的主要原因。结合原油族组分含量、饱和烃色谱总离子图，综合分析认为原油及族组分碳同位素倒转与前期成藏之后地层抬升引起的生物降解和油气的多期次充注有关，前期充注的原油中烃类组分多被微生物降解，而沥青质不易被降解得以保留，由于成熟度低，碳同位素值较低；而后期充注的高—过成熟度油中沥青质含量很低，以其他组分尤其是饱和烃为主，由于成熟度高，碳同位素值较高，甚至大于早期充注油的沥青质碳同位素值，使混合油中出现沥青质碳同位素与其他组分碳同位素倒转的现象。因此，塔河油田奥陶系原油成藏过程及其成藏之后的次生变化是碳同位素倒转的主要原因。

Origin of carbon isotopic inversion of Ordovician crude oil and group components in Tahe Oilfield,Tarim Basin

An in-depth analysis of carbon isotopic reversal mechanism of Ordovician crude oil and group composition in Tahe Oilfield, Tarim Basin is of great significance for understanding accumulation evolution and oil and gas exploration. The variation characteristics of carbon isotopes in plane and depth of 93 crude oils and group components are analyzed. δ¹³C asphaltene - non-hydrocarbon values in Aiding area, Tahe main area and Toputai area are -0.73‰,-0.63‰ and -0.58‰, respectively. The values are positive in area 9 and its surrounding areas as well as in southern pre-salt area. The inversion of δ¹³C saturated hydrocarbon and δ¹³C total oil occurs in some wells in Aiding area and Tahe main area. Carbon isotopes of asphaltene and other components and total oil are reversed with different degrees in different areas of Tahe Oilfield. However, the inversion distribution in depth is not correlated with the burial depth of crude oil, and the thermal effect caused by burial depth is not the main reason for the inversion of asphaltene carbon isotopes and other components in the Ordovician crude oil group in Tahe Oilfield. Combined with the contents of crude oil group components and total ion diagram of saturated hydrocarbon chromatography, it is concluded that the inversion of carbon isotope of crude oil and group components is related to biodegradation caused by formation uplift after early accumulation and multi-stage oil and gas charging. The hydrocarbon components in the early charged crude oil are mostly degraded by microorganisms, while the asphaltene is not easily degraded and retained, due to low maturity and light carbon isotopes. However, the asphaltene content in the late charged oil with high to over maturity is very low, and other components, especially saturated hydrocarbons, are the main components. Due to the high maturity, the carbon isotope of asphaltene is heavier, even heavier than that of the asphaltene carbon isotope in the early charged oil, the phenomenon of inversion of the asphaltene carbon isotope with other components occurs in the mixed oil. Therefore, the accumulation process and secondary changes of Ordovician crude oil in Tahe oilfield are the main causes of carbon isotope inversion.