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致密砂岩气藏的高毛细管力及强水湿性使其易产生水相圈闭损害,影响气藏及时发现、准确评价及经济开发。目前消除水相圈闭的物理化学方法,由于可能诱发其他储层损害,应用尚受到限制。选取鄂尔多斯盆地渗透率小于0.1×10-3μm2、介于(0.1~0.3)×10-3μm2之间和大于0.3×10-3μm2的致密砂岩岩样,利用氮气在恒定高压差与递增压差驱替原地有效应力下饱和模拟地层水岩样的实验,揭示致密砂岩水相自然返排行为。结果表明:随着时间增加,含水饱和度逐渐下降,渗透率越高,含水饱和度降低幅度越大,残余水饱和度越低;渗透率介于(0.1~0.3)×10-3μm2之间的岩样,在前150h递增驱替比恒定高压差驱替含水饱和度降低慢,但水相返排率更高。分析表明,致密砂岩水相圈闭损害严重,孔隙结构、渗透率和压力梯度是影响水相返排的重要因素,孔喉非均质性强的储层宜采用递增压差驱替的方式;水相返排过程包括驱替和蒸发2个阶段,当气相在不同孔喉中形成渗流通道后,可适当提高压差加速水相蒸发。
Tight sandstone gas reservoirs with high capillary strength and strong water wettability make it easy to produce water phase trapping damage and affect timely gas reservoir discovery, accurate evaluation and economic development. At present, the physicochemical methods to eliminate the trap of aqueous phase have limited application due to their potential to induce other reservoir damage. Tight sandstone samples with permeability less than 0.1 × 10-3μm2, between (0.1-0.3) × 10-3μm2 and greater than 0.3 × 10-3μm2 in Ordos Basin are selected to be replaced by nitrogen at constant pressure and incremental pressure difference Experiments of simulating the formation water and rock samples under the effective in situ stress revealed the natural backflow behavior of the tight sandstone water phase. The results show that with the increase of time, the water saturation decreases, the higher the permeability is, the greater the decrease of water saturation is, the lower the residual water saturation is. The permeability is between (0.1-0.3) × 10-3μm2 In the first 150 h, the incremental flood displacement is slower than the constant high pressure differential flood but the water saturation decreases more, but the water backflow rate is higher. The analysis shows that the tight sandstone has serious damage to the water traps, pore structure, permeability and pressure gradient are important factors affecting the return of the water phase. For the reservoir with high heterogeneity, Water phase return process includes two stages of displacement and evaporation. When the gas phase forms a seepage channel in different pore throats, the pressure difference can be properly increased to accelerate the water phase evaporation.