Abstract: Multi-scale science is a subject to study coupling phenomena and action mechanisms in distinct spatial or temporal scales. It is also the core of complexity science. The main contents, methods and advances for multi-scale studies are presented briefly. From the point of view of multi-scale science, oil and gas reservoirs are complex multiscale systems. Production of oil and gas are very complicated processes with spatial-temporal scales and series coupling processes in percolating channels such as pore throats and fractures. Multi-scale phenomena in oil and gas field development mainly include reservoir multi-scale description, multi-scale data integration and multi-scale simulation. Exemplified by tight sand gas reservoirs, multi-scale phenomena in the unconventional gas reservoir development are discussed. Multi-scale structure of tight sandstone gas reservoirs consists of matrix pores and throats, natural fractures and hydraulic fractures. Restriction of gas supply from tight matrix and formation damage are two key factors limiting gas well performance. According to multi-scale mass transport theory, application of reservoir protection during drilling, completion and stimulation and maximum reservoir contact technology should be emphasized for exploitation of unconventional oil and gas resources.

Key words: multi-scale science, reservoir, oil and gas field, fracture, spatial scale, temporal scale