Abstract:

Pore structure is an important factor that influences percolation capacity and oil production of low permeability reservoir. It is a hot spot in low permeability reservoir study. A quantitative method for pore structure evaluation which can characterize pore structure of heterogeneous reservoir on macro-scale is needed. Taking low permeability reservoir of Cretaceous in Tanan Depression as an example, based on thin slices observation, porosity and permeability test and capillary pressure test, this paper applied fractal algorism to reservoir pore structure evaluation, and established a quantitative pore structure evaluation method based on pore fractal dimension from mercury intrusion test. The result shows that there are four types of pore structures developed in the study area, including coarse shape type, subcoarse shape type, subfine shape type and fine shape type. Pore fractal dimension can be calculated according to the linear relationship between logarithm of capillary pressure and logarithm of wetting phase saturation. The smaller the pore fractal dimension is, the better the pore structure will be. The pore fractal dimension criteria for pore structures classification was built up with thin slice and oil testing. It is also found that large pores and small pores have different fractal characters in high heterogeneous reservoirs in the study area, which performs as the segmental character in the relationship between capillary pressure and wetting phase saturation.

Key words: converted wave, common conversion point, asymptotic method, target-oriented method