LITHOFACIES CHARACTERISTICS AND HYDROCARBON DISTRIBUTION PATTERN IN LACUSTRINE FINE-GRAINED SEDIMENTARY ROCKS OF THE PERMIAN LUCAOGOU FORMATION FROM THE SANTANGHU BASIN

Abstract

The Lucaogou Formation in the Santanghu basin is an important position for hydrocarbon storage and production in the west of China. Therefore, the lithofacies characteristics and hydrocarbon distribution pattern of the Permian Lucaogou Formation in Santanghu Basin are studied in this paper. Firstly, a series of qualitative descriptions and quantitative analyses was conducted on the Lucaogou Formation of Santanghu Basin, such as core description, petrographic thin section observation, scanning electron microscope (SEM) observation, X-ray diffraction, Soxhlet extraction, porosity and permeability analysis, oil saturation analysis, etc. From the series of descriptions and analyses, the Lucaogou Formation fine-grained sedimentary rocks can be classified into three lithofacies, which are organic-rich massive tuffaceous shale lithofacies (RMTSL), organic-rich laminated and cloddy diamictite lithofacies (RLCDL) and organic-lean massive dolomite lithofacies (LMDL). RMTSL contains the highest content of free hydrocarbon and solid organic matter and higher porosity. LMDL contains the lowest solid organic matter content and develops the least pores. RLCDL develop the largest number of cracks and fractures. In addition, commercial oil production mainly appears in RMTSL. Uplift belts that are away from erosion areas and develop thickness RMTSL will be areas with the most potential. However, slops deeper than fault surface, subsidence depositional centres and erosion areas only yield low production of hydrocarbon. Hence, the Mazhong uplift belt is the favourable area for hydrocarbon accumulation in Lucaogou Formation fine-grained sedimentary rocks.