Characteristics of natural and hydraulic fractures in tight oil reservoir in Ordos Basin and its implication to field development

Key words:  tight oil reservoir  natural fractures  hydraulic fractures  effective parameter  Ordos Basin

Abstract:

The characteristics of the fractures in a tight oil reservoir are the basis for the selection of oil exploitation modes and well pattern optimization. In this study, a Gauss function fitting method was adopted to investigate the coupling relationship among the natural fractures, fractures generated by hydraulic fracturing and in-situ formation stress. Using the effective parameters of the hydraulic fracturing via volumetric fracturing in the tight oil reservoirs, the effective length of the hydraulic fractures can be identified through the analysis of the pressure difference between fracture controlled and uncontrolled zones by fitting the production data of the horizontal wells according to the established flow model based on the natural energy development mode. On this basis, a numerical simulation model of typical wells can be established. By comparing the production predicted by the numerical simulation and the actual field data, the reliability of the above analysis method can be verified along with the coring observation from the inspection wells between the horizontal wells. The results show that the dominant direction of the hydraulic fractures is basically the same as that of the in-situ stress, and these reservoirs can be produced via a natural energy development mode. For the tight oil reservoirs with the dominant direction of the in-situ stress different from that of its natural fractures, water injection technique can be considered. For the cases studied in this paper, the average effective fracture width is less than or equal to 10 m.