| In serious heterogeneity reservoir, the high permeability zone often allows injected water to channel directly between injection wells and production wells. So other low permeable formation is not swept. It results in poor conformance efficiency and inferior recovery coefficient. At the same time, the production zones become more and more deep, the working conditions of water shut-off agents turn to be more and more harsh. For this reason, it is important to develop some new water shut-off agents suitable to harsh conditions. Since it is good injectivity, easy preparation, low cost and environment-friendly, soluble silicates become a kind of good choice. But soluble silicate water shut-off agents have much problems such as weak gel strength , short gelation time, etc. The objective of this paper is to research the basic properties (modulus, density, viscosity and pH value), special properties (temperature-sensitivity, salt-sensitivity, Calcium and ferrum-sensitivity and pH sensitivity), rheological property. Also, several kinds of application types such as silicic acid sol, precipitation, silicic acid gel, silicic acid microsphere, silicates/urea system are studied. By core tests, the plugging rate, residual resistance factors and oil recovery efficiency of all these application types is measured. The experimental results show that all have good plugging effects for harsh environments. To precipitation water shut-off agent prepared by water glass and calcium chloride, the visulazation experiments show that it surpresses the bottom-water fairly good and enhances oil production. According to theorical and experimental results, pilot tests put into practice on selected block. The pilot tests show that silicate precipitation can be used in high temperature ( at 108℃), low permeability (57×10-3μm2) formation and achived good effects on oil production increments and water cut reduction.
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