Abstract：

　　Most fracture-cavity carbonate reservoirs in the Sichuan Basin are water-bearing gas reservoirs and the gas-water two phase seepage mechanism is complex. However, the existing visual micromodels of gas-water two phase micro seepage are based on an ideal porous structure or casting sheet image, which cannot describe the distribution of pores, fractures and cavities in actual reservoirs. In addition, the research into mechanism is focused on the pore type and fracture type reservoirs, and there is a lack of the understanding of the cavity type and fracture-cavity type reservoirs. By combining the CT scanning technology and laser etching techniques, the CT scan images of fracture type, cavity type and fracture-cavity type carbonate cores in the Sinian system of the Sichuan Basin are used as the template to design and develop the three types of visual micromodels. Then the mechanism of gas-water two phase micro seepage and the formation mechanisms of trapped gas and irreducible water were studied. The quantitative characterization of gas-water distribution was also obtained by the gray scale analysis. The results show that the seepage mechanisms of three models are different in process of gas flooding and water flooding. The trapped gas caused by circumfluence, cut off phenomenon and blind corners is prevalent in three types of models. In addition, the special trapped gas is also remains in “H” channels, “dumbbell-shaped” channels and micro-fracture channels. The irreducible water films on the channel walls, the round water group in the middle of the cavities, the water columns into the narrow throats are the main forms of residual water. The fracture type model has the most serious water channeling phenomenon, the shortest water-free production period and the lowest recovery efficiency, while the cavity type model has a uniform water drive front, the longest water-free production period and the highest recovery efficiency. This study provides an accurate description of gas-water two phase micro-seepage mechanisms of different formations in fracture-cavity carbonate reservoirs. This provides a theoretical basis for the efficient development of similar gas reservoirs.

Key words： fracture-cavity carbonate reservoirs gas-water two-phase flow visual micromodels trapped gas irreducible water gray intensity analysis

Received： 22 December 2016

Corresponding Authors：杨胜来, yangsl@cup.edu.cn

Cite this article：WANG Lu,YANG Shenglai,LIU Yicheng等. Visual experimental investigation of gas-water two phase micro seepage mechanisms in fracture-cavity carbonate reservoirs[J]. Petroleum Science Bulletin, 2017, 2(3): 364-376.

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