砂岩储层应力敏感性及其对单井产能的影响——以四川盆地JQ气田为例

Stress sensitivity of sandstone reservoirs and its impact on well productivity:A case study of JQ gas field in Sichuan Basin

近年来,四川盆地JQ气田致密砂岩储层展现出良好的勘探开发潜力。然而,在油气藏开发实践过程中,致密砂岩储层岩石存在应力敏感伤害,将影响气井产能。为了明确储层岩石应力敏感性及其对单井产能的影响,助力气藏的高效开发,针对四川盆地JQ气田中侏罗统沙溪庙组致密砂岩储层,在地层温度下开展变围压和变回压两种方式应力敏感性评价实验。结果表明:①变围压方式下储层岩石渗透率损失率在78.83%~95.85%,应力敏感普遍偏强。②变回压方式下储层岩石渗透率损失率在1.48%~64.02%,渗透率较低的样品,应力敏感表现为无~弱;渗透性越好,应力敏感越强。③6号砂体的应力敏感比8号砂体强。④应力敏感对气井产能有较为严重的影响,产量由1.75×10^(4)m^(3)/d降至0.17×10^(4)m^(3)/d,升降出口压力次数越多,获得的产量越低。因此,在制订生产措施时,渗透能力好的储层或压裂改造后的储层应选择合适的生产压差,防止在过高的生产压差下,喉道、裂缝提前闭合,尽可能降低应力敏感程度,提高单井产能和采收率,保障致密砂岩气藏的长期稳产。

In recent years,the tight sandstone reservoirs in the JQ gas field of the Sichuan Basin have shown good exploration and development potential.However,in the process of development,the reservoir rocks may be damaged due to stress sensitivity,which will affect the productivity of gas wells.In order to clarify the stress sensitivity of reservoir rocks and its impact on single-well productivity for purpose of efficient development of gas reservoirs,a stress sensitivity evaluation experiment was carried out for tight sandstone reservoirs of the Shaximiao Formation in the JQ gas field,at formation temperature and in two pressure states(variable confining pressure and variable back pressure).The results are obtained in four aspects.First,at variable confining pressure,the reservoir rocks have the permeability loss rate of 78.83%-95.85%,with strong stress sensitivity generally.Second,at variable back pressure,the reservoir rocks have the permeability loss rate of 1.48%-64.02%.Samples with lower permeability exhibit non-to weak sensitivity of stress.The better the permeability,the stronger the sensitivity.Third,the stress sensitivity of sandbody No.6 is stronger than that of sandbody No.8.Fourth,the stress sensitivity has a serious impact on gas well productivity,with the production decreasing from 1.75×10^(4)m^(3)/d to 0.17×10^(4)m^(3)/d.The higher the frequency of lifting and lowering the outlet pressure,the lower the resulting yield.Therefore,to make a production strategy for reservoirs with good permeability or stimulated reservoirs,appropriate production pressure difference should be chosen so as to prevent premature closure of throats and fractures under excessively high production pressure differences.Moreover,stress sensitivity should be reduced as much as possible,in order to improve the well productivity and recovery,and ensure the long-term stable production for tight sandstone gas reservoirs.