莺歌海盆地LD区块地层超压对泥岩成岩作用的影响及其地质意义

在综合前人研究基础上,应用X衍射、薄片鉴定、热解分析、生物标志化合物研究等技术,并与邻区的常压环境下的相关特征进行了对比,深入分析了莺歌海盆地LD区块地层超压的分布状况及其对黏土矿物转化和有机质热演化的影响。结果表明,①研究区内,超压顶界面深度从盆地中心向边缘逐渐变深;②研究区内,超压顶界面之上,随埋深和地温的增大,蒙脱石、伊蒙混层中蒙脱石和高岭石的含量逐渐降低,而伊利石和绿泥石含量逐渐增加,但超压顶界面附近及往下时,黏土矿物各组分的含量几乎不再减少,受到了地层超压作用的抑制;③Pr/nC₁₇和Ph/nC₁₈随深度增大而降低,但在强超压顶界面以下,变化趋势发生逆转,出现微弱增大的趋势,超压顶界面以下的实测R_o值即有机质的成熟度也出现了明显的低异常。地层超压通过抑制黏土矿物转化,间接减弱了储层的胶结作用,有利于深层优质储层的形成。研究区地层超压抑制了有机质的热演化,地层超压对生烃的抑制作用扩大了研究区有效源岩的层位和体积,并使主力源岩的生、排烃期后移,从而有利于油气的晚期快速聚集成藏。 

Effects of Formation Overpressure on Mudstone Diagenesis and Its Geological Significance in LD Block of Yinggehai Basin

According to previous studies,we applied a serious of techniques,such as X-ray diffraction,thin section analysis,pyrolysis analysis and biological marker analysis,and then compared the related characteristics between the study area and adjacent normal pressure areas.Based on the previous work,we made a further analysis on the distribution of overpressure in LD block and its effects on clay mineral transformation and thermal evolution of organic matter.The results show that:①In study area,the depth of the top interface becomes deeper from basin center to margin.②Over the interface of overpressure,with the increase of depth and geotemperature,the content of montmorillonite,illite mixed montmorillonite and kaolinite gradually decreased,while the content of illite and chlorite increased.However,below the interface of overpressure,content of every component in clay mineral almost has no change which inhibited by formation overpressure.③With the increase of depth,the ratio Pr/nC₁₇ and Ph/nC₁₈ decreased.While below the interface of strong overpressure,the trend reversed and even appeared slight increase.R_o values,the maturity of organic matter,which are measured below the overpressure interface,also appeared significantly abnormal lower.Overpressure indirectly weakens the reservoir's cementation by inhibiting the transformation of clay minerals,which promotes the formation of deep and high-quality reservoir.Overpressure in the study area inhibits the thermal evolution of organic matter.The inhibiting effect of overpressure on hydrocarbon generation enlarges position and volume of the later valid source rock.It delays the hydrocarbon-generating and expulsion times of main source rock,which contributes to the late hydrocarbon accumulation.