湖相沉积背景下改进的TOC计算方法

An Improved Method for TOC Calculation in Lacustrine Sediments

湖相页岩油的沉积环境为陆相深湖或半深湖沉积,岩性复杂,传统的Δlog R法只适用于海相沉积背景下的页岩油储层,急需寻找适用于湖相背景下页岩油总有机碳含量(TOC)的评价技术。因受岩性影响(尤其是在灰质和泥质较重影响的情况下),电阻率和声波时差测井曲线的幅度差会发生变化,原本在非生油的页岩段电阻率和声波时差值一致时的基线发生偏移,导致传统Δlog R法计算的TOC值偏离实际值,需要对受岩性影响的层段进行声波时差和电阻率曲线进行校正。筛选明显受灰质和泥质影响的含有机质层段的声波时差和电阻率值,确定受岩性影响的电阻率和声波时差质心所在位置,校正使其回归到不受岩性影响的声波时差和电阻率的线性关系(基线)上,即将确定受岩性影响的声波时差和电阻率的质心点通过校正到不受影响的质心点上,从而排除岩性对测井曲线的影响,实现页岩层段TOC值的准确计算。以研究区济阳坳陷博兴洼陷和利津洼陷为例,通过岩性校正,湖相沉积背景下改进的Δlog R法所预测出的TOC值与实测值的相关系数达90%以上。与传统的Δlog R法相比,精度提高30%~40%,证明改进的Δlog R法适用性强,具有一定的推广性。

The sedimentary environment of lacustrine shale oil is continental deep lake or semi-deep lake sediment,and the lithology is complex.The traditionalΔlog R method is suitable for shale oil reservoirs under Marine sedimentary background,but the method is limited,and it is urgent to find a suitable evaluation technology for TOC of shale oil under lacustrine background.In order to solve the problem that the amplitude difference of resistivity and acoustic time lag log will change due to lithology,especially in the case of heavy gray and mud,the original baseline deviation when the resistivity and acoustic time lag value are the same in non-oil-generating shale section causes the TOC value calculated by traditionalΔlog R method to deviate from the actual value.The acoustic lag and resistivity curves of the interval affected by lithology need to be corrected.The acoustic time difference and resistivity values of organic-containing intervals significantly affected by gray matter and mud are screened,the centroid locations of the resistivity and acoustic time difference affected by lithology are determined,and the linear relationship(baseline)between the acoustic time difference and resistivity unaffected by lithology is corrected.The centroid of acoustic time difference and resistivity affected by lithology will be corrected to the unaffected centroid,thus eliminating the influence of lithology on log value and realizing the accurate calculation of TOC value in shale section.Taking Boxing sag and Lijin sag of Jiyang depression in the study area as an example,the correlation coefficient between TOC and measured values predicted by the improvedΔlog R method under lacustrine sedimentary background is about 90%through lithology correction.Compared with the traditionalΔlog R method,the accuracy is improved by 30%~40%,and the improvedΔlog R method has strong applicability and certain extensibility.