高演化海相烃源岩元素地球化学评价:以四川南江杨坝地区下寒武统为例

Element Geochemistry Evaluation of Marine Source Rock with High Maturity:A Case Study of Lower Cambrian in Yangba Section of Nanjiang County,Sichuan

评价高演化海相烃源岩已成为国内油气勘探的难点.尝试以四川南江杨坝地区下寒武统烃源岩为例,利用元素地球化学参数建立高演化海相烃源岩评价的新方法.在计算得到与海洋自生有机质相关的自生元素含量基础上,通过聚类分析将成因作用相同的自生元素聚为一类,并建立指示有机质沉积环境及基本属性的参数与自生元素含量之间的线性关系,从而优选出与有机质富集密切相关的自生元素,并利用因子分析得到4个反映有机质从形成、沉积到埋藏过程中环境变化的主因子,最终得到能够反映烃源岩的形成条件优劣的公式.依此对南江杨坝下寒武统烃源岩的品质进行划分.实践证明,该方法可为高演化海相烃源岩的评价提供一些新思路.

How to evaluate the marine source rocks with high maturity is of crucial importance. Element geochemical indexes are used to build a new evaluating method for source rock in this study. In this paper, the samples are from the Lower Cambrian in Yangba section of Nanjiang County, SichuarL We used the measured Xxs （a relative excess of X compared to titanium in post-Archean Australian shale）, the authigenetic elements from the the same environment are treated as a class. Then, illustrate the linear relation between each of TOC, δ13 Ccarb and δ13 Corg and the authigenetic elements from the same class, optimize the authigenetic elements that have closely relationship with enriched organic matter. Finally, the factor formula is built to indicate the changing of the quantity and quality of organic matter during the process of formation, deposition and burial according to the factor analysis. This formula is used to divide the rank of source rock quality of the Lower Cambrian in Yangba section. Thus, this geochemistry evaluation method would provide some new ideas for identifying and evaluating the marine high maturity source rocks.