Abstract:

There are two types of fractures in the muddy gravel and the tuffaceous dolomite in Qingxi oilfield, Jiuquan Basin. By applying many kinds of techniques, the characters of fracture pattern, log response and reservoir quality in different lithofacies are systematically studied, and the diagenesis of controlling fracture is thoroughly analyzed. The results show that gravel-edge fractures, corrosion fractures and structure fractures are formed in muddy gravel rocks; lay fractures, extrusion fractures and structure fractures formed in tuffaceous dolomite. The fracture systems not only improve mainly the  permeability, but also increase the porosity. The selective(diverse)corrosion diagenesis of parent rock is the main factor, which controls the forming of fractures and secondary pores. There are several mineral components in muddy gravel and the key reason to muddy gravel fractures is the replacement of the framework grain and cement, the dissolutions of the cement and dissolvable grain. Dual and trinal structures are the key to fracture systems in the tuffaceous dolomite, which includes strong dolomitization and laumontitization in carbonitites.

Key words: Qingxi oilfield, Jiuquan Basin, muddy gravel, tuffaceous dolomite, fracture feature, diagenesis, selective(diverse)corrosion