有限空间温压共控热模拟油气产物地球化学特征

生烃反应是烃源岩在有限的地层孔隙空间内受温度、上覆地层静岩压力、地层孔隙流体压力等多种因素相互作用的过程,而热模拟实验是正演研究有机质生烃反应的常见手段。但较多的热模拟实验受仪器装置的限制,仅考虑了温度的作用,与实际地质演化存在较大差异。选取泌阳凹陷泌215井古近系核桃园组泥岩样品,分别进行了有限空间温压共控和温控热模拟实验,通过族组分、同位素、GC、GC-MS等方法分析了2种模拟实验条件下的油气产物。结果表明:①有限空间温压共控热模拟残留油饱和烃可以保存至较高的演化阶段;②相同模拟温度下,有限空间温压共控热模拟残留油的饱和烃参数Pr/Ph值、Pr/C17值大于温控热模拟实验,饱和烃生物标志物参数值C2920S/(20S+20R)、C29ββ/(αα+ββ)等小于温控热模拟实验;③有限空间温压共控热模拟的烃类气体δ^13C值大于温控模拟实验。上述现象主要是由于有限空间温压共控热模拟实验中高压孔隙流体的存在延缓了热成熟和原油裂解反应过程。因此,在开展热模拟实验研究时应考虑研究区是否发育超压、地层水等因素,其直接关系着热模拟实验结果的地质适用性。

Geochemical characteristics of hydrocarbon products under thermal simulation of temperature and pressure co-control in finite space

Hydrocarbon generation reaction is comprehensively affected by temperature,static pressure,and pore pressure of strata in the limited pore space of the source rocks,and the thermal simulation experiment is a useful method to model hydrocarbon generation of organic matter. However,many thermal simulation experiments are limited by instrumentation,and only consider the effect of temperature,which is obviously different from the actual geological conditions. Here,the Hetaoyuan Formation mudstone of Well B215 in Biyang Depression is selected as samples to conduct simulation experiment of temperature and pressure co-controlling in finite space and that of only temperature-controlled,respectively. The oil and gas products under the two experiments have been analyzed by group composition,isotope,GC,GC-MS. The results indicate that:(1)The saturated hydrocarbons from residual oil can be preserved at a higher evolution stage under the condition of temperature and pressure co-control in finite space;(2)Under the same simulation temperature,the parameters Pr/Ph,Pr/C17 of the residual oil saturated hydrocarbons are higher in temperature and pressure co-control thermal simulation experiment,while the parameters C2920 S/(20 S+20 R)and C29ββ/(αα+ββ)etc. of residual oil steroids and terpenoids are smaller than those of temperature-controlled experiment;(3)The value of carbon isotope δ^13C of hydrocarbon gas under the thermal simulation of temperature and pressure co-control in finite space is higher than that of temperature-controlled thermal simulation. The above phenomena are mainly caused by the existence of high-pressure pore fluid,which delays the process of thermal maturation and crude oil cracking under the simulation experiment of temperature and pressure co-control in finite space. Therefore,the potential overpressure and formation water in the study area should be considered when conducting thermal simulation experiment,since it directly affects the geological applicability of the simulation results.