川西致密砂岩气藏岩心狱渗区的界定方法

A method to determine permeability jail boundaries of tight sandstone cores from the Western Sichuan Basin

在渗透率低于0.05 mD的致密砂岩气藏的相对渗透率曲线中,可能存在气、水两相均无法有效流动的狱渗区。对川西致密砂岩气藏岩心狱渗区内气、水两相流动规律的研究,需以狱渗区的合理界定为前提。针对川西致密砂岩气藏岩心狱渗区的界定问题,通过定义等渗点相对渗透率因子、气相相对渗透率曲率因子和水相相对渗透率曲率因子特征参数,提出一种考虑岩石及流体特征的狱渗区界定方法。采用该方法对川西致密砂岩气藏岩心的狱渗区进行界定,并探讨狱渗区对致密砂岩气藏气井生产的影响。研究结果表明,川西致密砂岩气藏岩心狱渗区集中在含水饱和度为63%~91%的区域内,接近储层的初始含水饱和度(为40%~70%)。开发时,由于钻完井、储层改造工作液残留在储层中,可能导致近井带含水饱和度上升至狱渗区内降低气井产量。狱渗区对致密砂岩气藏气井产气量的影响在生产初期达到最大,可导致产气量峰值的出现推迟数百天。

Permeability jail,where both gas and water cannot flow effectively,may exist in the relative permeability curve of cores of tight gas reservoirs whose permeability is below 0.05 mD.The investigation of gas and water flow in the permeability jail of the tight sandstone cores in the Western Sichuan Basin should be based on the reasonable determination of permeability jail boundaries.A method to determine permeability jail boundaries of the tight sandstone cores from the Western Si?chuan Basin was proposed.Factors including relative permeability factor at the cross-over point,gas relative permeability curvature factor and water relative permeability curvature factor were defined to describe the properties of rock and fluids.The method was applied to study permeability jail boundaries of tight sandstone cores from the Western Sichuan Basin.And the influence of permeability jail on gas production of the tight sandstone gas reservoir was analyzed.Results show that permeability jail of tight sandstone cores from the Western Sichuan Basin occupies water saturation region ranging from 63%and 91%,which approximates the initial water saturation of the Sichuan Basin(40%-70%).During the gas development,due to drilling,well completion and hydraulic fracturing fluids retention in the reservoir,water saturation near wellbore areas can rise to permeability jail and then reduce gas production.The permeability jail has the most significant effect on gas production at the beginning of the production in the tight sandstone gas reservoir.It can delay the peak gas production for hundreds of days.