致密砂岩气藏水相圈闭损害自然解除行为研究

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。

Spontaneous Removal Behavior of Water Phase Trapping Damage in Tight Sandstone Gas Reservoirs

Water phase trapping of tight gas reservoir caused by its high capillary pressure prevents gas reservoirs from being detected,precisely evaluated and economically developed.The present physical and chemical methods for removal of water phase trapping is seldom applied because that they might cause other damages.The experiments of N2 displacement to stimulate formation water tight sandstone core samples with the permeability of less than 0.1×10^-3μm，(0.1-0.3)×10^-3μm，and more than 0.3×10^-3μm² are conducted under the conditions of in situ stress and constant flow pressure difference or increased pressure differences to recognize the water flowback behavior in tight sandstone.The results indict that water saturation of core samples decreases gradually,and the lower the permeability of cores is,the lower the decrease rate of water saturation will be,and that the decrease rate of water saturation of core with the permeability of (0.1-0.3)×10^-3μm² displaced by increasing pressure difference is lower than that displaced by constant pressure difference within 150 hours,but the water flowback rate of core displaced by increasing pressure difference is higher.The analysis of results show that water phase trapping is severe.Pore throat structure,permeability and pressure gradient are the most important factors.The process of water flowback from cores includes two effects,water displaced by gas and water evaporation due to gas flow.If the pressure difference of water flowback increases properly,it will accelerate water evaporation effect when gas can flow through different sizes of pore throats.