Influence of Thermal Maturity on the Time-Resolved Emission Spectrum (TRES) Fluorescence Lifetime Characteristics of Crude Oils: A Preliminary Study Based on a Thermal Simulation Experiment of Crude Oils

Abstract

The time-resolved emission spectrum (TRES) fluorescence lifetime characteristics of crude oil have great application potential to classify the oil type and reveal its origin in a multisource petroleum system. However, the influence of thermal maturity on the TRES fluorescence lifetime characteristics of crude oil is still unclear. This study collected typical crude oil samples from deep reservoirs in the Tabei area of the Tarim Basin and obtained a group of pyrolyzed oils with different maturities by a thermal simulation experiment. The TRES average fluorescence lifetime value (τA) and profile pattern (λ–τ) of both pyrolyzed and crude oil samples were investigated. The results indicate that, with increasing maturity, the τA values of pyrolyzed oil slightly increase when EasyRo < 0.90% but decrease when EasyRo > 0.90%. Meanwhile, the λ–τ pattern shows no obvious changes when EasyRo < 1.53% but changes significantly when EasyRo > 1.53%. Based on the TRES fluorescence lifetime characteristics, the deep crude oils in various blocks of the Tabei area are divided into TB-I and TB-II types, which correspond well with their physical properties, diagnostic biomarkers, and carbon isotopic values. The TB-I crude oils are widely distributed in the Shunbei, Hadexun, Repu, and Halahatang blocks. This type of crude oil has a short τA value and exhibits an obvious platform pattern in its λ–τ profile. The TB-II crude oils are distributed only in the Yuke block. This type of crude oil has a long τA value and shows a unimodal pattern in its λ–τ profile. The TRES fluorescence lifetime parameters can effectively classify crude oils with different sources and can further identify the thermal maturity of crude oils with the same sources by combining them with the physical and geochemical parameters of crude oils, which exhibits great application potential to crude oils and individual petroleum inclusions in deep multisource petroleum systems.