Abstract:

Previous studies showed that R/S analysis of well logs can effectively characterize the degree of reservoir fractures. But R/S calculation only using acoustic curves cannot avoid the influence of lithology changes. In this paper, R/S calculation using the reconstructed curves (AC-GR) could remove the influence of lithology changes on acoustic curves and could reserve the response of fractures. In this way, R/S analysis of reconstructed curves (AC-GR) can much effectively characterized the development and location of fractures. Statistics showed that the relationship between fracture density and fractal dimension (D) of reconstructed curves (AC-GR) was good. In this study on dividing the flow units, in addition to the commonly used parameters, ie. porosity, permeability and effective thickness, the fractal dimension (D) of reconstructed curves (AC-GR) was also used in the method of cluster analysis. Taking the first oil layer in the eighth member of the Yanchang Formation in Jiyuan area of Ordos basin as an example, four types of flow units were defined according to the comprehensive flow ability. The first type was located in the confluence of main channel where the reservoir property and the effective thickness were high and the fractures were developed. The second was located in the main channel where the effective thickness was high and fractures were developed moderately. The third was located in the river flank where the effective thickness was low and fractures were developed. The fourth was sporadically distributed along the northeasttosouthwest direction in the areas where the reservoir property was not good and fractures were not developed.

Key words: R/S analysis, fractal dimension, fracture development, flow unit