透镜状砂岩储层压裂规模的优化问题

An optimal design of the fracturing treatment for lenticular sand reservoirs

实践证明,压裂改造储层是高效开发气藏的有效手段,其优化设计是需要考虑的重要方面。根据Elkins理论,储层渗透率越低,施工规模愈大,支撑裂缝越长,压裂后产量越高。但作业现场表明,透镜砂岩储层的压后产量与压裂规模的关系并不完全遵循Elkins理论,即压裂后的产量不单纯随着压裂规模的增大而增加,而存在一个适度的最优化压裂规模问题。为此,以四川盆地马井气田侏罗系蓬莱镇组储层为例,从地质构造、矿物沉积等角度分析了透镜状砂岩储层的成因和特点,从地应力方向、储层展布特征、裂缝评估、试井分析、压后效果统计等方面论证了透镜状砂岩储层对压裂规模的限制作用。基于储层厚度、砂体横向展布及压裂裂缝延伸特征,提出了透镜状砂岩储层压裂改造优化设计的方法,并成功地进行了现场应用。其成果对于我国类似透镜状砂岩储层的压裂优化设计具有指导借鉴作用。

Field practices have shown that hydraulic fracturing is one of the most effective means to enhance the recovery of gas reservoirs.In any case,an optimal design should be focused on at first before the hydraulic fracturing is to be done.According to the Elkins' theory,the lower the reservoir permeability,the larger the scale of fracturing treatment is;the longer the propped fracture,the higher the well production after fracturing is.However,actual field operations show that,as for lenticular sand reservoirs,the relationship between their production after fracturing and the scale of the fracturing does not always obey the Elkins' rule.Particularly,their production after fracturing will not simply grow with the increase of the scale of fracturing treatment,that is,an optimal fracturing treatment scale exists.Therefore,through a case study of gas reservoirs in the Jurassic Penglaizhen Formation of the Majing Gas Field,Sichuan Basin,the origins and features of a lenticular sand gas reservoir were analyzed in terms of geological structures and mineral deposit.Moreover,the restriction of a lenticular sand reservoir on fracturing treatment scale was demonstrated from the aspects of the in-situ stress direction,reservoir distribution characters,fracture evaluation,well test analysis,and post-frac result analysis.Based on the characteristics of reservoir thickness,lateral spread characteristic of sand bodies,and fracture propagation,an optimal design method of fracturing stimulation of a lenticular sand gas reservoir is proposed and is also successfully applied in the field operations.This provides guidance to the optimal design of fracturing treatment for similar lenticular sand gas reservoirs.