Kinetics of the hydrocarbon generation process of marine source rocks in South China

The kinetics of hydrocarbon generation of different types of marine source rocks and planktonic algae in South China were analyzed using the Rock-Eval 6 instrument and the Optkin kinetic software. The average activity energy of marine source rocks has the characteristics of EAIΔEII2>ΔEII1>ΔEI, the hydrocarbon generation speed is VmI>VmII1>VmII2>VmIII, while the planktonic algae has a very low activation energy for hydrocarbon generation and can generate a great abundance of heavy oil during the immature –low mature period. According to the results of kinetic experiments on thermal simulation experiments and simulation residue samples, the kinetic hydrocarbon generation process of marine source rocks can be described by four stages: (1) heavy oil generation, where the vitrinite reflectance (Ro) is 0.3%–0.6%, and the average activation energy is about 220 kJ/mol; (2) normal oil generation, where the vitrinite reflectance is 0.6%–1.2%, and the average activation energy is approximately 250–270 kJ/mol; (3) condensate and gas generation, where the vitrinite reflectance is higher than 1.2% and the average activation energy is higher than 270 kJ/mol; and (4) gas “dead line” of kerogen, where the vitrinite reflectance is higher than 4.21% and the average activation energy is higher than 320 kJ/mol.

摘要利用Rock-Eval 6热解仪和Optkin动力学软件对中国南方不同类型海相烃源岩和浮游藻进行了生烃动力学分析。研究表明，海相烃源岩的生烃平均活化能表现为EAⅠ＜EAⅡ1＜EAⅡ2＜EAⅢ，在干酪根转化率10%～90%的有效生烃期间，生烃活化能跨度ΔE呈ΔEⅢ＞ΔEⅡ2＞ΔEⅡ1＞ΔEⅠ，最大生烃速率呈VmⅠ＞VmⅡ1＞VmⅡ2＞VmⅢ；浮游藻生烃活化能很低，可在未熟—低熟期大量生成重质油。结合热模拟实验和模拟残样动力学分析认为，海相烃源岩的生烃动力学过程可以分为4个阶段：重质油形成阶段，Ro值在0.3%～0.6%，生烃平均活化能在220 kJ/mol左右，小于250 kJ/mol；正常原油形成阶段，Ro值在0.6%～1.2%，生烃平均活化能在250～270 kJ/mol左右；凝析油和天然气生成阶段，Ro值大于1.2%，生烃平均活化能大于270 kJ/mol；干酪根生气死亡线，Ro值大于4.21%，生烃平均活化能大于320 kJ/mol。