储层沥青拉曼光谱特征及其对油气成藏期次的约束——以冀中坳陷杨税务潜山为例

Raman Spectroscopic Characteristics of Reservoir Bitumen and Its Constrain on Stages of Hydrocarbon Accumulation——Take Yangshuiwu Buried Hill of Jizhong Depression as an Example

快速准确确定油气成藏的时间及期次对于深入了解油气成藏机制与分布规律有着重要的意义。储层沥青作为油气成藏的标志物,通过对其分析有助于了解油气运移通道和准确判定油气成藏的时间。以杨税务潜山为例对储层沥青进行了系统的拉曼光谱分析。杨税务潜山储层沥青主要分布在最晚形成的裂缝中,少数充填在孔隙中。沥青在紫外光下基本不发荧光,属于炭质沥青。沥青的拉曼光谱特征相对比较稳定,具有明显的D峰和G峰,对于同一储层样品的不同测试点,D峰和G峰位置变化不大,但是背景噪声影响比较明显,拉曼谱图在1500 cm^-1之后具有明显的抬升。首先扣除原始拉曼光谱的背景值,然后采用洛伦兹分峰拟合方法对沥青拉曼光谱进行了分峰拟合,直到拟合的谱图曲线与原始谱图形态基本一致为止。在拟合好的谱图曲线上直接读取D峰和G峰的峰高(H)、半高宽(FWHM),峰位差(vG-vD)、以及D峰和G峰之间的最低值(S)等参数,计算双峰之间的鞍型指数(saddle index),根据公式Ro%(cal)=-3.291+7.432log(vG-vD)-0.306log(saddle index)-2.935logFWHMG-3.118logFWHMD计算沥青的成熟度。结果显示储层沥青具有非均一性,指示油源具有混源特征,成熟度主要分布在两个区间,Ro分别为1.00~1.37和1.44~1.94。结合埋藏史确定杨税务潜山的油气成藏时间主要有两期,第一期为东营期(35~25 Ma)阶段,凝析油和湿气充注;第二期为明化镇—现今(5 Ma~0)阶段,以天然气为主充注。研究结果与研究区烃源岩生排烃史吻合,油气类型与杨税务潜山现今油气藏特征一致。研究表明,拉曼光谱技术可以对储层不同位置的沥青进行微区分析,并可以获得高精度的光谱数据,基于光谱数据可以准确确定沥青的成熟度。因此,基于储层沥青拉曼光谱定量表征和成熟度定量计算,结合盆地埋藏史和热史模拟,可以准确确定油气成藏的期次和时间。该方法具有快速准确、成本低的特点,展示了很好的应用前景。

The quick and accurate determination of the hydrocarbon accumulation time and period is of great significance to understanding the mechanism and distribution rules of this process.As a marker of the hydrocarbon accumulation,bitumen is an important factor in the analysis of hydrocarbon migration path and the exact time of its accumulation.This article was based on systematic research on the Raman spectroscopy of bitumen in the Yangshuiwu buried hill reservoir.The bitumen in this reservoir is mainly distributed in the later formed cracks,and few are filled in the pores.Bitumen almost has no fluoresce under ultraviolet light,so it can be catalogued to carbonaceous bitumen.The experimental results show that the bitumen in this area has relatively stable Raman spectrum characteristics,with obvious D-peak and G-peak that do not change from different test points in the same stratum.However,the background noises may be changed at a different point.The Raman spectrum goes up after 1500 cm^-1.When processing the Raman spectrum data,the background value was subtracted from the original data firstly,and then the Lorentz peak-differentiation method was used to fitting the peaks,until the fitted spectrogram curve is basically consistent with the original shape.The peak height(H)of D-peak and G-peak,the full width at half maximum(FWHM),the distance between D and G,the lowest value between D-peak and G-peak and other parameters were obtained directly from the fitted curve.Saddle index can be calculated by these parameters,and the bitumen maturity was also calculated by the formula.The results of the calculation indicate that the reservoir bitumen is heterogeneous,which means the oil is multi-sourced.The bitumen maturity parameters are mainly distributed in two areas,with Ro=1.00~1.37 and Ro=1.44~1.94,respectively.Combined the bitumen maturity parameters with the burial history to determine the Yangshuiwu buried hill hydrocarbon accumulation time,two periods of accumulation were confirmed,condensate and moisture gas accumulation stage of Dongying period(35~25 Ma)and natural gas charging stage of Minghuazhen-present(5 Ma~0).Results are consistent with the hydrocarbon generation history of the source rocks in the study area.This study shows that Raman spectroscopy can perform micro-analysis of bitumen in different positions in the reservoir,obtain high-precision spectral data,and then calculate the maturity of bitumen accurately.Therefore,quantitative characterization of reservoir bitumen Raman spectrum and quantitative calculation of maturity,combined with simulation of basin burial and thermal history,the exact time and period of hydrocarbon accumulation can be determined.This method is fast,accurate and inexpensive,therefore has a promising application prospect.