In view of the poor physical property and the complicated geological conditions of the difficult recovery reservoir in Qaidam Basin, the physical properties and the micro pore structure characteristics of the reservoir in 3 main blocks are systematically studied by means of the constant-rate mercury injection technique, the nuclear magnetic resonance and the nonlinear seepage experiment. In the comprehensive evaluation of low-permeability reservoirs, we add a new parameter, the brittleness index. Thus, a comprehensive evaluation method for the low-permeability & difficult recovery reservoir is proposed. It is indicated that the difficult recovery reservoir is typically a low porosity and ultra-low permeability reservoir. The differences of the physical properties and the pore-throat characteristic parameters of the reservoir in different blocks are due to the differences of the micro-pore structures of the reservoir. Meanwhile, the exploitation potential of the difficult recovery reservoir of Qaidam Basin is analyzed and evaluated. The classification results are consistent with the actual development and production of the oilfield.

Qaidam Basin  /  low-permeability & difficult recovery reservoir  /  pore structure  /  rock brittleness index  /  reservoir evaluation