Abstract:

The Chang 6³ low reservoir in Yanchang Formation in upper Triassic system in Huaqing area, Ordos basin is the extra low permeable oil layer, and the natural fracture distribution and validity restrict petroleum exploration and development. Based on the statistics method and associating with the rock failure criteria and the strain energy method, the fracture development degree and distribution were quantitatively predicted in the Chang 6³ reservoir in Huaqing area by the finite element simulation of the aeolotropism reservoir. According to the quantitative observations of the fractures in orientated drilling cores and thin-slices, The fracture distribution network conceptual model of Chang 6³ reservoir was preliminarily erected based on the characteristic parameters of fracture direction, interval, and density, which expressed the essential states of the fractures in the reservoir, including the natural fracture density, distribution pattern and the difference of the fracture composition. And according to the fill degree, fill probability and mechanical property of the constructional surfaces of the fractures in the reservoir and the included angle between the fracture strike and the direction of the maximum horizontal principal pressure, the validity of the fracture systems in the reservoir were preliminarily analyzed. It was held that the invalid fractures were dominant in the reservoir, which had reached 85.6%, while the valid ones only 14.4%. And after hydraulic treatment, the NEE-NWW natural fracture systems were easy to be reconstructed or change to valid ones, which could improve the vadose capacity of reservoir. These results could offer important geological reference for the further oil exploration and the reasonable development decision in the Chang 6³ reservoir in Huaqing area.

Key words: fracture, reservoirs, fracture distribution network conceptual model, current stress field, fracture validity, Huaqing area, Ordos basin