Pore-throat structure characteristics of tight reservoirs of the Middle Permian Lucaogou formation in the Jimsar Sag, Junggar Basin, northwest China

The Middle Permian Lucaogou Formation in the Junggar Basin, China is a typical tight oil reservoir. Thin sections, helium porosity and permeability, X-ray diffraction, X-ray computed tomography, and focused ion beam scanning electron microscopy were used to analyze 11 core samples with different oiliness from the Lucaogou Formation. Muddy siltstone, tuffaceous siltstone, dolomitic siltstone, and sandy dolarenite are the primary rock types in the Lucaogou tight oil reservoirs with different oil saturations. The dolomite content of the Lucaogou tight reservoir is positively correlated with porosity and permeability, suggesting that dolomite has an important influence on reservoir quality. Sandy dolarenite and dolomitic siltstone are characterized by a high dolomite content with the largest pore and throat radii and have a higher pore-throat network connection ratio with higher permeability and better oiliness. Thus, the quality of the Lucaogou tight reservoir is primarily controlled by the dolomite content.