Total Scanning Fluorescence Characteristics and Implications of Shale Oil in the Lucaogou Formation, Jimsar Sag, Junggar Basin, NW China

Abstract

The Lucaogou Formation in the Jimsar Sag is a typical lacustrine shale oil development area where the first large-scale shale oil field in China was discovered, and a large number of studies have been conducted on the genesis and distribution of the shale oil in this formation. However, few detailed studies have been conducted on the comparison between the characteristics of the hydrocarbons in the shale and the adjacent tight reservoirs in the same shale sequence package. In this study, the total scanning fluorescence (TSF) quantitative fluorescence technique, which has been rarely applied to and studied in the Lucaogou Formation in the Jimsar Sag, was used to conduct systematic quantitative fluorescence analysis of the shale, tight reservoirs, and crude oils in the Lucaogou Formation. The geochemical analysis was also carried out for all samples. The results revealed that the shale, tight reservoirs, and oils have similar single-peak TSF spectrograms, and different values of the TSF parameters in the Lucaogou Formation. The TSF parameters R1 and R2 values of the blocky shale, fractured shale, tight reservoirs, and produced oils are decreased successively. The TSF parameters can be used as indicators of hydrocarbon composition, physical properties, thermal maturity, migration, and oil-producing layers. The values of TSF parameters R1 and R2 are generally smaller in the upper section of the Lucaogou Formation (P2l2) than in the lower section (P2l1), indicating that the hydrocarbons in the upper section have better physical properties and higher thermal maturity. The distribution of TSF parameters R1 and R2 in the upper section of the Lucaogou Formation is relatively scattered, indicating that the hydrocarbons have undergone obvious lateral migration. Based on the TSF parameter comparison of core and oil samples, it was preliminarily determined that the shale oil in the upper and lower sections of the Lucaogou Formation was mainly produced from the tight reservoirs in the shale sequence. The results of this study provide new data and ideas for fine studies of the shale oil in the Lucaogou Formation in the Jimsar Sag.

Paleo-Sedimentary Environment and Formation Mechanism of the Organic-Rich Shale of the Permian Lucaogou Formation, Jimsar Sag, Junggar Basin, China

“…Typically, the formation exhibits a thinning trend from east to west. Based on a regional maximum flooding surface, the Lucaogou Formation can be subdivided into a lower member (P2l1) and an upper member (P2l2) (Figure 1d) [1][2][3].…”

“…The Permian Lucaogou Formation is the main source rock in the Jimsar Sag and the main stratum for shale oil exploration. The Lucaogou Formation has a complex lithology and strong heterogeneity [1]. The multiple sets of interbedded high-quality source rocks are mainly composed of siliceous and carbonate shales, while the tight reservoirs are mainly composed of siliceous and carbonate siltstones (Figure 1d).…”

“…The Jimsar Sag, located in the southeastern part of the Xinjiang Junggar Basin, is an important oil exploration area in China (Figure 1) [1][2][3][4]. The Permian Lucaogou Formation in the Jimsar Sag, one of the important shale oil targets in China, had produced a total of 1.51 million tons of shale oil by the end of 2021, with an annual oil production of 42.6 × 104 t (2.98 million barrels) [5].…”

Role of Organic Matter, Mineral, and Rock Fabric in the Full-Scale Pore and Fracture Network Development in the Mixed Lacustrine Source Rock System

“…The Permian Lucaogou Formation from Jimusar Sag (Figure b) is a hot shale oil resource target. − The Jimusar Sag (Figure b) has been the first national shale oil demonstration area in China in 2020 . The sweet-spot intervals from the upper and lower Lucaogou Formation contribute to the majority of shale oil production.…”

“…49−51 The Jimusar Sag (Figure 1b) has been the first national shale oil demonstration area in China in 2020. 52 The sweet-spot intervals from the upper and lower Lucaogou Formation contribute to the majority of shale oil production. Until 2020, a total of 52 vertical wells and 37 horizontal wells have been drilled; among them, the total shale oil production from the 28 production wells is as high as 370 t/d.…”