边缘凹陷烃源岩有机质丰度曲面预测法——以渤海湾盆地莱州湾东北洼为例

沉积盆地边缘凹陷具有地层变化快和非均质性相对较强的特点，导致利用传统测井和地震属性方法预测烃源岩总有机碳含量（TOC）的可靠性低。为此，结合电阻率、声波时差和密度等测井曲线与实测TOC值，采用三元二次最小二乘法进行曲面拟合预测烃源岩TOC值，在渤海湾盆地莱州湾东北洼烃源岩有机质丰度预测中取得了较好的效果。该方法具有两个优点：首先，采用原始测试数据直接进行拟合，消除了基线拾取和热变指数取值时产生的人为误差；其次，将密度这种反映岩石组分的综合指标纳入预测控制因素的范畴，更好地控制了有机质对各测井数据的响应。预测结果表明：在沉积早期，TOC值的一个高值带分布于洼陷沉积中心，到后期受构造迁移和抬升作用影响，TOC值高值带向四周扩散、高值降低、直至闭合状高值带消失；TOC值的空间分布表现为由老到新有机质丰度逐渐降低的特点，因此沙三段为主要烃源岩。

A fitting prediction method of TOC in source rocks in a marginal sag: A case study of northeastern sag in Laizhou Bay,Bohai Bay Basin

The prediction of TOC in source rocks in marginal sags with conventional logging and seismic attributes is often unreliable due to its strata fast change and strong heterogeneity.To solve this problem, we propose a novel prediction approach.This is a ternary quadratic least square TOC prediction based on resistivity, acoustic moveout, density logging data, and measured TOC data.We apply this approach to the northeastern sag in Laizhou Bay, Bohai Bay Basin, and achieve good results.This approach has two advantages.First original test-data direct fitting eliminates the human error during baseline picking and LOM value selection.Secondly the density involved in the prediction can constraint the response of organic matters on well logging data.According to our prediction, a high TOC value belt distributes in the center of the sag in the early deposition.Due to tectonic migration and uplift in the later period the this belt diffuses to the periphery and the high value decreases and disappears.The TOC spatial distribution is characterized by the gradual decrease from old to new strata.Based on the prediction, Es₃ is the main source rock.