射孔参数对砂砾岩储层压裂的影响

Impact of perforation parameters on fracturing of glutenite reservoirs

砂砾岩油藏具有应力差大、破裂压力高的特点,导致造缝难度大,如何降低破裂压力是安全压开储层的关键。将水泥与石英砂按3∶1混合并随机混入不同直径的鹅卵石和细碎石粒,制作边长300 mm的人造砾岩,使用水力喷砂射孔枪进行射孔,通过改变角度0~90°、深度1.5~6 cm模拟现场不同射孔方位角和炮眼深度,根据现场数据设置实验三向应力分别为9.4、19.3、24.8 MPa,排量为50 mL/min,压裂液黏度为45 mPa·s,开展室内水力压裂实验,分析射孔角度和射孔深度对裂缝起裂及破裂压力的影响。研究结果表明,射孔方向与最大水平主应力夹角为0°时破裂压力最低,为11.9 MPa,减小射孔方位角能够降低破裂压力3.55 MPa;射孔深度由1.5 cm增加至6.1 cm,破裂压力降低了4.63 MPa;当射孔孔眼附近存在砾石,破裂压力异常增高约10 MPa。建议通过合理优化射孔方位角,适当增加射孔深度,同时遴选砾石粒径较小且分选性较好的层段进行施工,提高压裂改造成功率。研究成果为制定玛湖射孔方案提供了参数优选的依据。

Glutenite reservoirs are characterized by large stress differences and high fracture pressures,leading to great difficulty in fracturing,and how to reduce fracture pressure is the key to safely fracture the reservoirs.Mix cement and quartz sand in a ratio of 3∶1 and randomly mix different diameters of pebbles and fine gravel particles,to prepare artificial glutenite with side length of 300 mm,which were then perforated with hydraulic sand jet gun.By changing the angle from 0 to 90°and the depth from 1.5 to 6 cm,onsite different perforation azimuths and perforation depths were simulated.Based on field data,the three-axis stresses were set to be 9.4,19.3 and 24.8 MPa,respectively.And then,a displacement of 50 mL/min and(fracturing fluid with)a viscosity of 45 mPa·s were selected to perform indoor hydraulic fracturing experiments,to analyze the effect of perforation angle and depth on fracture initiation and fracture pressure.The research results show that when the angle between the perforation direction and the horizontal maximum principal stress is 0°,the fracture pressure is the lowest at 11.9 MPa.And reducing the perforation azimuth can reduce the fracture pressure by 3.55 MPa,while increasing the perforation depth from 1.5 cm to 6.1 cm reduces the fracture pressure by 4.63 MPa.When gravel is present near the perforation,the fracture pressure increases abnormally by about 10 MPa.It is recommended to optimize the perforation azimuth,increase the perforation depth appropriately,and select the intervals with smaller gravel particle size and better selectivity for construction to improve the success rate of fracturing.The research results may provide a basis for selecting parameters in optimizing perforation schemes for Mahu glutenite reservoir.