临兴致密气压裂液全过程渗吸伤害规律

致密砂岩气作为重要的非常规天然气资源,需经过压裂改造才能实现有效开发。压裂施工中由于毛管力作用压裂液的渗吸现象会造成储层渗透率降低,从而降低采收率,因此开展压裂过程中压裂液渗吸伤害机理研究对储层保护和提高压后产能具有深刻意义。以临兴致密气区块为研究对象,通过室内渗吸实验模拟从压裂到返排整个过程中压裂液与储层之间的渗吸作用机理,探究了渗吸液相、压裂液黏度、岩心渗透率以及渗吸时间四种因素影响下的压裂液渗吸伤害规律,并利用灰色关联法量化分析各因素对渗吸伤害的影响程度。研究结果表明:压裂液黏度和压后焖井时间与储层伤害率呈正相关关系,与返排率呈负相关关系;岩心渗透率与伤害率呈负相关关系,与返排率呈正相关关系;压裂液渗吸对储层的伤害率较地层水大,返排率则低于地层水;各因素对致密砂岩气储层渗吸伤害的影响程度大小排序为:压裂液黏度压裂液渗吸时间岩心渗透率。研究结果为压裂施工现场的压裂液体系优选及焖井时间控制提供参考。

Study on Imbibition Damage Law of Linxing Tight Gas Fracturing Fluid in the Whole Process

As an important unconventional natural gas resource, tight sandstone gas can only be effectively developed through fracturing. Due to the imbibition phenomenon of fracturing fluid caused by capillary force in a fracturing operation, the reservoir permeability declines, resulting in the reduction of the recovery factor. Therefore, the study on the mechanism of fracturing fluid''s imbibition damage during the fracturing has profound significance for reservoir protection and productivity improvement after fracturing. Linxing tight gas block was used as the research object in this study, where the indoor seepage experiment was used to simulate imbibition mechanism between fracturing fluid and the reservoir during the whole process from fracturing to flow back period. The characteristics of imbibition damage were further explored under the influence of four factors including imbibition liquid phase, fracturing fluid viscosity, core permeability and imbibition time. The degree of imbibition damage caused by each of these factors were quantitatively analyzed via gray correlation method. According to the results, fracturing fluid viscosity and the plugging time after fracturing exhibit a positive correlation with the reservoir damage rate, and show a negative correlation with the flow back rate; the core permeability exhibits a negative correlation with the damage rate while showing a positive correlation with the flow back rate; compared with the formation water, the fracturing fluid imbibition has a higher damage rate to the reservoir but has a lower flow back rate; the influence degree of various factors on imbibition damage of tight sandstone gas reservoir are ranked as follows: fracturing fluid viscosity > fracturing fluid imbibition time > core permeability. A reference for the fracturing fluid system optimization and the control of shut-in time can be provided by the results.