Characteristics and Controlling Factors of High Quality Deep Conglomerate Reservoir: A Case from Lower Cretaceous Qingshuihe Formation of Gaoquan Structure Zone in Sikeshu Sag, Junggar Basin

High-production oil flow was obtained from Lower Cretaceous Qingshuihe Formation in Well Gaotan-1, which is located in the southern margin of Junggar Basin. The result proves that high-quality conglomerate reservoirs are developed in Qingshuihe Formation. In this paper it analyzes the rock minerals, physical properties, pore structure and diagenesis of the conglomerate of Qingshuihe Formation in Gaoquan structure zone, Sikeshu sag, by using cores and thin section data, porosity-permeability analysis and X-ray diffraction whole rock mineral analysis. The main controlling factors of high-quality conglomerate reseroirs were analyzed based on the result. The studies show that the tuffaceous gravels are the major content of the reservoir. The content of sandy grains is typically less than 50%. Based on the contact relationship of the gravels and the content of sandy grains, the conglomerate can be divided into grain supported conglomerate and matrix supported conglomerate. The reservoir space is strong in heterogeneity, which is dominated by primary pores. The development of reservoir space is affected by a variety of diagenesis, among which physical compaction is the major contributor to the porosity loss. The conglomerate reservoir has undergone the burial process of early long-term shallow burial and late rapid deep burial, and is currently in the mesogenesis stage A. The forming of high-quality conglomerate reservoir derives from the following controlling factors. Conglomerate from underwater distributary channels in fan-delta front is the foundation to form high-quality reservoir. Low geothermal gradient and the the burial process of early long-term shallow burial and late rapid deep burial are key contributors to the formation of the reservoir. The alkaline diagenetic environment in the early stage of diagenesis and later acid diagenetic environment, as well as the overpressure are also important to the formation of the reservoir.