Shenmu - Mountain Region Upper Paleozoic Sandstone Reservoir Water Lock Mechanism

Low-permeability and tight sandstone gas reservoir is the most promising and most important energy reality for our country in the 21st century. Shenmu -shuangshan region of Upper Paleozoic sandstone reservoirs has the characters in common with other low permeability gas reservoirs in Ordos Basin, which is called " three low factors and two high factors" ,referring to low permeability, low porosity and low pressure ,high capillary pressure and high effective stress ,and the ultra - low water saturation phenomenon as well.Water blocking ,an capillary pressure-causing effect ,is one of the crucial reasons for the situation ,which is generalized as that each well will not have a good production after the gas was found. So, we should continue to deepen our understanding of the mechanism and the affective factors of the water blocking, so as to provide a theoretical basis for the rational and efficient development of the Low-permeability gas reservoir.In this paper, a large amount of experimental research work was carried out, focusing on the theory of water blocking. The main results achieved are:1) The representative experimental cores with different characteristics of lithology, pore structure and interstitial material were selected through basic experimental study;2) The basic assessment of water blocking was set up through a series of experimental study, such as experiment designed to analyze the differences between permeability tested with gas and liquid, pressure-sensitive experiment, water-sensitive experiment;3) The process of gas migration was simulated, and the mechanism of the ultra-low water saturation was understood through the simulated core-flow experiments;4) Through the two-phase flow experiments, the rule of the water saturation reduction and gas permeability restoration, different water damage degree under different evaluative basic, the influences of temperature and stress on water damage, as well as the influences of different working fluids on water damage were all investigated;5) The impact of the liquid loading was discussed through the anti-imbibition simulation experiments;6) The effects of production pressure increase, ethyl alcohol injection and CO₂ injection to relieve water damage were evaluated through several experiments;7) According to experimental results of water blocking, a comprehensive analysis of the affecting factors of water block was proceeded.