Quantitative characterization of microfractures in the Cretaceous tight reservoirs from the Liuhe Basin

Abstract

Microfractures can obviously improve physical properties and connectivity of tight reservoir, which is an important factor to control the exploration and development of tight oil and gas. However, there is little quantitative research on microfracture, thus, its reservoir mechanism is not clear. Taking the Cretaceous tight reservoir in the Liuhe Basin as an example, the microstructure characteristics of fractures were discussed on micron and nanometer scale respectively, and their contribution to physical properties was revealed in this paper. The results show that a small number of intercrystalline pores, intergranular pores and dissolution pores are developed in the Cretaceous tight reservoirs, and microfractures are the main reservoir space. The width of nano-sized fracture is mainly in the range from 2 nm to 300 nm, in which the proportion of fractures with larger width increases obviously with the increase of buried depth, and its contribution to pore volume is also greater. The width of micron-sized fracture is mainly in the range from 2.95 μm to 114 μm, and micron-sized fracture is much more developed with the increase of burial depth. Although the distribution frequency of micron-sized fracture is much smaller than that of nano-sized microfracture, it makes a greater contribution to permeability.

Keywords

• Microfracture
• Reservoir space
• Quantitative characterization
• Tight reservoir
• Liuhe Basin