温度与有效应力对页岩储层应力敏感影响研究

摘要

At the beginning of shale gas exploitation,hydraulic fracturing is bound to damage the reservoir temperature field, resulting reservoir temperature variation, which is conducive to produce thermal stress on shale reservoirs.During the process of depletion exploitation,the formation pressure depletes slowly, but the effective stress to the rock grain increases. The effective stress may cause the elastic or plastic deformation, and this deformation makes the permeability become sensitive to effective stress. Therefore, it is essential to know that stress sensitivity is influenced by temperature and effective stress. The method of confining pres-sure variation is applied. By means of testing of permeability of shale samples under differ-ent stresses and temperature, the reduction property of permeability is obtained. The results demonstrate that the shale permeability behaves in an exponential manner with the tempera-ture variation,and the higher initial permeability would lead to the stronger stress sensibility. The shale permeability still presents in the obvious exponential relationship with the change of effective stress,it decreases with the increase of the effective stress, which is consistent to stress sensitivity of low or ultra-low permeability reservoirs.The stress sensitivity damage for shale permeability is at middle level through the evaluations of stress sensitivity, the damage rate of permeability drops to 0.33 from 0.45 with the temperature rising. Shale has middle stress sensitivity when the effective stress reaches 17 MPa from 13 MPa, whereas the stress sensitivity damage is at weak level for the situation that the effective stress rises from 17 MPa to 21 MPa.%在页岩气藏开发初期,水力压裂改造必会破坏储层温度场,致使储层温度发生变化,进而储层产生热应力,在衰竭式开采过程中,地层压力逐渐下降,以上过程造成作用岩石颗粒上的有效应力增加,页岩储层产生应力敏感,使得储层渗透率减小,从而影响气井产能.为此,为了明确温度与有效应力对储层应力敏感性的影响,采用恒内压变围压试验方法,以页岩岩心为试验对象,进行不同有效应力、温度下储层物性应力敏感试验.研究结果表明,初始渗透率越高,则应力敏感性越强,温度对应力敏感性影响越大,渗透率与温度具有较好的指数关系.当有效应力由小增大时,储层渗透率由大变小,其下降幅度由大到小,渗透率与有效应力同样呈现较好的指函数关系,这与低渗透、特低渗透油气藏应力敏感性呈现相同的规律.同时,通过应力敏感评价得出,页岩渗透率的应力敏感程度为中等,且随温度的升高,渗透率损害率由0.45降低到0.33.有效应力从13 MPa增加到17 MPa时,应力敏感程度为中等,而有效应力从17 MPa增加到21 MPa时,应力敏感程度却为弱.