高硫干酪根生油过程与化学结构演化

With the continuous exploitation of petroleum in the worldwide oil fields, the proportion of sulfur-containing and high-sulfur crude oil is gradually increasing. The formation of high-sulfur crude oil is closely related to the thermal evolution of high-sulfur kerogen. Identifying the structural forms and organic sulfur distribution characteristics in kerogen during hydrocharbon generation contributes to comprehensive understanding of the chemical properties of high-sulfur kerogens and the mechanism of formation of sulfur-containing oil, and also promotes the production and desulfurization of high-sulfur oil. It has been reported that high-sulfur kerogen generates oil at considerably lower thermal maturities than ordinary kerogen. However, there are different opinions about the mechanism of the early hydrocarbon-generation of high-sulfur kerogen. Previous studies were focused on Tpye II-S kerogen deposited in marine environment and comprehensive analysis of sulfur in kerogens from terrestrial saline lacustrine was obviously inadequate. In this study, we intend to experimentally simulate oil generation of immature lacustrine Type I-S kerogen of Qianjiang formation from Jianghan Basin in a closed Au tube pyrolysis system and then analyze the composition and structure of insoluable kerogen residue after hydrocarbon generation using Rock-Eval, elemental analysis, 13C NMR, XPS and XANES technique and to develop the models of Type I-S kerogen with different maturity, aiming to improve understanding the mechanism of early formation of high-sulfur crudes at the molecular level.

随着世界范围内油田的不断开采，原油资源中含硫、高硫原油的比例逐渐增大。高硫原油的形成与高硫干酪根热演化有密切联系，对生烃过程中硫在干酪根中赋存形式及转化研究有助于准确全面的了解高硫干酪根的化学性质和高硫原油的生成机理，进而促进高硫油的勘探开发和合理利用。高硫干酪根可以在较低的温度下裂解生油，但目前对其生烃机理尚有争议。前人主要针对海相II-S型干酪根进行了研究，对陆相盐湖沉积盆地形成的高硫干酪根研究较少。本项目拟利用黄金管高温高压生烃体系，模拟盐湖相成因江汉盆地潜江组未熟烃源岩I-S干酪根生烃，对生油后的高硫干酪根残渣进行Rock-Eval热解、元素分析、13C NMR、XPS能谱及XANES谱分析，对I-S型干酪根及其生油后残渣结构变化、干酪根中硫的赋存状态转化进行研究，建立不同成熟度条件下高硫干酪根的分子结构模型，为深入研究高硫干酪根的生烃机理提供分子层面的科学依据。

世界原油供应日趋劣质化，高硫原油产量占比逐渐增大。中国的高硫原油主要产自盐湖相沉积盆地，其母质来源及形成过程与海相成因的高硫干酪根有明显差别。国外学者普遍认为高硫干酪根通常与海相成因的II型干酪根密切相关，对干酪根中硫的赋存状态研究大多以海相成因的II-S干酪根为研究对象,对于中国湖相成因的I-S干酪根中硫的赋存形态研究很少，对于生烃过程中干酪根中硫的赋存形态演化研究更为罕见。江汉盆地是中国最为典型的盐湖盆地之一，对该盆地潜江组高硫烃源岩I型干酪根生烃后残渣结构变化、硫元素的结构赋存形式变化进行研究，对于对更加全面的理解高硫原油的生成机理有重要帮助。.本项目主要通过对江汉盆地潜江组高硫烃源岩干酪根进行黄金管高温高压封闭体系生烃模拟实验，对实验残渣进行元素分析、高精度固体碳核磁共振（13C DP/MAS NMR）、硫的X射线吸收近边光谱（S-XANES）分析等，系统研究了潜江组盐湖相干酪根生烃过程中干酪根结构变化及含硫官能团的赋存转化；干酪根中硫的元素含量随成熟增大呈现先增大后减小趋势，与氧元素的变化趋势相似。固体碳核磁共振研究指示在热模拟区间干酪根结构呈现三段式变化。在Easy%Ro 0.80-1.00 区间，脂碳结构断裂速率加快，由硫的XANES光谱分析显示在热模拟成熟度区间,有机硫结构中硫化物、噻吩类结构随成熟度增大呈现先减小后增大的变化趋势，在Easy%Ro 0.75时两者的相对丰度降到最低。亚砜结构在Easy%Ro 0.65 时完全断裂，有机硫结构相较脂碳结构的更早断裂说明活性有机硫结构的断裂启动了干酪根结构中C-C的快速裂解。此外不仅有机硫化物的断裂对生烃过程具有促进作用，噻吩类及亚砜结构也不同程度影响了干酪根裂解生烃。噻吩类结构相对丰度在Easy%Ro 0.75后逐渐增大，指示了随成熟度增大，干酪根中硫的赋存状态趋向于芳香化。硫醇结构相对丰度随成熟度增大呈现逐渐增大趋势，对促进生烃贡献不大。