The Reservoir Sensitivity of Triassic Baikouquan Formation in Mahu Depression

Abstract

The Triassic Baikouquan Formation in the slope area of the Mahu Depression is the largest glutenite reservoir in the Junggar Basin, with low porosity and permeability; however, its physical properties are poor, the distribution of oil and gas is quite different, and the output fluctuates greatly. It is of great guiding significance to study the sensitivity characteristics of the reservoir for oil and gas development and productivity design. In this paper, the reservoir of the Triassic Baikouquan Formation in the Mahu Depression of Junggar Basin is taken as the research object, and the geological characteristics, pore structure characteristics and clay mineral characteristics of the reservoir are investigated through the use of X-ray diffraction and scanning electron microscope; moreover, the sensitivity of velocity, water, salt and stress of the reservoir are studied through the use of a sensitive flow test. The research results show that the lithology of the reservoir is mainly glutenite, composed of tuff and metamorphic mudstone, and the minerals are mainly Yimeng mixed-layer clay minerals, with fine particle size, average porosity of 10.5% and an average permeability of 9 × 10−4 μ m2, forming pore structures such as dissolved pores, cemented pores and intergranular gaps, which belong to the poor pore structure reservoir with low porosity and low permeability. The velocity-sensitive damage rate of reservoirs in the study area is between 4 and 46, and the reservoirs are moderately weak and poor in velocity sensitivity. The damage rate of the reservoirs’ water sensitivity in the study area is between 36 and 58, which can be defined as medium–weak and medium–strong water sensitivity. The reservoir in the study area contains clay minerals in a Yimeng mixed layer, which easily hydrate and swell, and the clay minerals in different parts of the Yimeng mixed layer are different, resulting in great differences in salt sensitivity at different depths. The maximum permeability damage rate of the reservoir is 80%, the irreversible permeability damage rate is 20%, and the stress sensitivity is weak. The research results provide theoretical data support for adopting targeted reservoir protection measures in the process of oil and gas exploration, development and construction.