基于误差分析的ΔLogR技术在长岭龙凤山烃源岩评价中的应用

The application of ΔLogR technology based on the error analysis for source rock evaluation in Longfengshan Sag,Changling Faulted Depression

长岭断陷龙凤山次凹下白垩统烃源岩埋藏深,取心井分析资料少,利用常规的烃源岩有机地球化学分析难以表征烃源岩段有机碳的分布特征。以现有取心井样品分析化验资料为基础,利用ΔLogR技术可以对烃源岩有机碳含量进行精细刻画。传统ΔLogR模型在基线值、叠合系数确定等方面存在主观性大、具有区域适用性等问题,因此利用改进的ΔLogR模型及最优K值分析ΔLogR与实测有机碳含量之间的关系,减小计算误差。但是在两者的趋势之外仍存在许多异常点,这些异常点所产生的误差大大降低了计算有机碳含量的准确性。通过综合研究发现,烃源岩层段异常点存在的原因主要包括扩径、薄夹层及数据分析3个方面。异常点的剔除,能有效改善ΔLogR模型计算有机碳含量的精度,使计算结果与实测值相关系数R2达80%以上,能够客观反映烃源岩层有机碳含量。应用结果显示,龙凤山次凹下白垩统沙河子组为主力烃源岩层系,有机碳含量主要集中在1.0%～3.0%之间,营城组下部为次要烃源岩层系,有机碳含量较低,主要集中在0.6%～1.0%之间。

It is difficult to characterize organic carbon distribution of source rock by conventional organic geochemical methods for faulted strata in Longfengshan Sag,Changling Faulted Depression,since the burial depth of source rocks is deep and cored wells analysis data is few.Based on cored wells analysis data,organic carbon content of source rock can be described usingΔLogRtechnology.There are many problems,such as subjectivity and regional applicability of baseline value,the composite coefficient.As a result,the relationship betweenΔLogRand the organic carbon content can be analyzed using improvedΔLogR model and optimal K and it can reduce the calculation error.However,there are many outliers in logging evaluation model of source rocks and the reason for outliers include diameter extension,thin interbed and data analysis.By removing outliers,empirical formula for quantitative calculation of organic carbon can be obtained.The coincidence rate between calculated and measured values is up to 80%and the result can objectively reflect the organic carbon content of source rock.Results show Shahezi Formation is the main source rock,with organic carbon content ranged from 1.0%-3.0%,and lower part of Yingcheng Formation is the secondary source rock,with organic carbon content ranged from 0.6%-1.0%.