Controlling factors of carbonate cement and its influence on oil-water distribution of the Neogene Shawan Formation in the northern Chepaizi area, Junggar Basin, NW China

摘要

The distribution of physical property of the Neogene Shawan Formation(N1s) in the north of Chepaizi area (Abbreviated as "Chebei area") is characterized by "double peak", which is mainly related to carbonate cements in the reservoirs. It is observed that the large amounts of early carbonate cements are present in thin sections, which are inhomogeneously filled in some primary intergranular pores and caused strong heterogeneity of the reservoir. On the basis of convent calculate of carbonate cement in core, AxioVision image analysis with multiple times and multiple fields of view was used to supplement the calculation of carbonate cement content, and the relative error compared with the core measurement result was -0.14, which effectively compensated for the lack of core measurement data points. The content of carbonate cement has been characterized by "higher in the north area and lower in the south area" on the plane. The carbonate cement is formed in closed diagenetic environment with good sealing ability and water body stagnated alternately. The closed diagenetic environment of the Shawan formation in Chebei area primed the environmental foundation for the growth of carbonate cements, and the abundant Ca2+ in the formation water primed the material foundation for the growth of carbonate cements. The difference in Ca2+ content in formation water determines the distribution difference of carbonate cements, and the diagenetic environment is the controlling factor for the development of carbonate cements. The complex oil-water distribution in the study area is principally related to the carbonate cementation. The super heavy oil with high viscosity cannot enter the low porosity and permeability reservoir with tough cementation, which is prone to the phenomenon of oil-water inversion.