Abstract:

Profitable oil and gas flows of over 1,000 m ³/d have been obtained from the sandstone reservoir of the Cretaceous Qingshuihe formation in the Sikeshu sag of the southern margin, Junggar basin, which proves that the formation belongs to a set of high-quality reservoir. Based on the analysis of outcrop sections and drilling data and using polarizing microscope, pore and permeability analyzer and confocal laser scanning microscope, the paper analyzes the rock mineral, physical property and pore structure of the sandstone samples from the Qingshuihe formation and carries out researches on diagenetic evolution by combining with its burial history. The results show that the sandstone of Qingshuihe formation mainly containing feldspar lithic sandstone and lithic sandstone is characterized by a little matrix, medium content of cements and developed residual intergranular pores, which is at the Phase A of the middle diagenetic stage with the compaction dominated by pore reduction. The comprehensive analysis shows that the formation of the high-quality reservoir in Qingshuihe formation is controlled by 3 key factors such as early long-term shallow burial and late rapid deep burial, developed fractures and abnormal high formation pressure. The early long-term shallow burial and the late rapid deep burial are favorable for preservation of primary pores in the reservoir; both intragranular microfracture and bedding fracture are developed, which is helpful for the formation of efficient flowing paths in the sandstone reservoir; and the abnormal high formation pressure contributes to the preservation of intergranular pores and the opening of fractures.

Key words: Junggar basin, Cretaceous, Qingshuihe formation, reservoir characteristic, main controlling factor, diagenetic evoluation, abnor- mal high pressure, burial history