Fluid Inclusions in the Carboniferous igneous reservoirs: Implications for the timing of petroleum accumulation in the Well PEN1 western sag of Junggar Basin

Carboniferous igneous reservoirs in the West Depression of Basin 1 Well, Junggar Basin, are crucial for oil and gas exploration. This field holds significant geological importance in the region. In this paper, we employ polarized light microscope observation, temperature measurement of fluid inclusions, and basin simulation to establish the hydrocarbon filling period and reservoir formation time of the Carboniferous volcanic reservoirs by analyzing the morphology of the fluid inclusions and their homogeneous temperature characteristics. The findings indicate that: The igneous reservoir in the Carboniferous period, located in the West Depression of the Basin 1 Well, primarily contains hydrocarbon brine inclusions, hydrocarbon gas inclusions, and pure gas inclusions. Oil inclusions typically manifest as bands in quartz grain cracks and calcite filled cracks, with blue-green and blue-white fluorescence indicating medium-maturity and high-maturity crude oil, respectively. Please note that technical term abbreviations will be explained upon first usage. The hydrocarbon inclusions in the Carboniferous volcanic reservoir in the West Depression of Basin 1 well contain oil, gas, and gas-liquid two-phase brine inclusions with a diverse temperature distribution. These inclusions exhibit characteristics of multi-peak distribution, suggesting that the hydrocarbon fluids in the study area were infused during multiple stages. Based on the homogeneous temperature test of the fluid inclusions and the simulation results of the burial and thermal history of the sedimentary strata from a single well, it is preliminarily confirmed that there are two phases of hydrocarbon formation in the study area. The early phase occurred mainly from the Late Triassic to Jurassic period, while the late phase occurred mostly from the Late Cretaceous to Late Tertiary period. Technical term abbreviations are explained upon initial usage. Biased language has been eliminated, and clear, objective language employed. This study offers a fundamental theoretical foundation to elucidate the mechanism of oil and gas formation in the Carboniferous igneous reservoirs of the West sag in Basin 1 Well.