The different water shutoff treatments based on in-situ gelation are attractive technologies; however, the field results often fall short of expectation. Reason of unsuccessful treatments might be that the flow resistance against water often develops not in the right time and reservoir space. Therefore, the primary aim of the research project was to develop such chemical systems, which will form the blocking phase triggered by mixing with water. As a novelty, water sensitive petroleum solutions and external microemulsions were developed, which are stable until they are diluted with water forming thus stable water external macroemulsions. Phase inversion of such metastable systems to stable ones in reservoir may radically restrict the water flow through their high viscosity and entrapment of the dispersed particles by the pores. The transformation and structure of phases were analyzed by photon correlation spectrometry, rheometry. The core studies confirmed that all metastable systems reduce the flow of water by 80–90% in water-saturated sandstone. Using chemical-free postflush the flow resistance remains substantial against water; meanwhile the permeability deterioration against gas is negligible.

The petroleum microemulsions are in phase of pilot test in two gas wells in the largest Hungarian oil/gas reservoir (Algyő field) with the aim at restricting the substantial water production. The concept and the developed technology is similar to the earlier silicon microemulsion field test, which yielded 3 106 m3 incremental gas production in the same reservoir and measurable decrease in water production. The metastable systems may offer an excellent opportunity for water shutoff in matured gas fields and gas storage facilities. The unique properties of the techniques are that flow resistance may occur only in water saturated reservoir space and in case of technical failure; the flow barrier can be eliminated by oil and gas injection.

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