摘要
定面射孔技术是为了提高体积压裂改造效果而提出的一种新的射孔方案。根据岩石力学及流-固耦合理论,建立了定面射孔地层的三维弹塑性流固-耦合地应力模型,采用数值方法进行求解,结合最大拉应力准则,研究了定面射孔水力裂缝的起裂规律。经过大量计算发现:定面射孔条件下,裂缝首先在射孔面内的射孔眼起裂,然后射孔眼相互贯通而形成扇形裂缝面,增大了水力裂缝的波及体积及井筒的连通性;同一平面内两侧孔眼在中间孔眼上产生的附加应力降低了Y方向主应力而增大了X方向和Z方向主应力,导致正断层采用定面射孔时,起裂压力较大,起裂压力随射孔方位角的增大而降低,只有当射孔方位角大于60°时,定面射孔起裂压力低于螺旋射孔起裂压力;对于逆断层,射孔方位角越小,起裂压力越低,且均低于螺旋射孔起裂压力;减小射孔间夹角、增大射孔直径及深度均可降低起裂压力。
The set surface perforation is the latest perforating technology which is proposed to improve fracture volume effect. Based on the theory of fluid-solid coupling and rock mechanics, a three-dimensional elastic-plastic fluid-solid coupling stress model for set surface perforation in stratums is developed. Based on the maximum tensile stress criterion, the crack rule of hydraulic fracture is obtained by numerical simulation. It can be seen from abundant calculations that under the condition of set surface perforation, crack first initiates in the perforation of the perforating plane, and then extends in the perforating surface to form a fan-shaped fracture surface, which increase the swept volume of hydraulic fracture and the wellbore connectivity. Both sides of the perforation produce additional stress in the middle perforation to reduce the principal stress of Y direction within the same plane and increase the principal stresses of the X and Z directions. Thus it is the reason that when set surface perforation is adopted for the normal fault, under a larger crack stress, the greater the perforation azimuth angle, the lower the crack pressure. Only when the perforating azimuth angle is greater than 60°, the set surface perforation crack pressure is lower than that of spiral perforation. For reverse fault, the smaller the perforation azimuth angle, the lower the crack pressure, and the crack pressure is lower than that of spiral perforation at any time. Reducing the angle between perforation and perforation, increasing the perforation diameter and depth can reduce the crack pressure effectively.
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2016年第12期3393-3400,共8页
Rock and Soil Mechanics
基金
国家973项目(No.2015CB250900)
国家自然科学基金项目(No.51374074)
中石油基金(No.2013D-5006-0210)联合资助~~
关键词
定面射孔
流固耦合
起裂压力
裂缝形态
数值分析
set surface perforation
fluid-solid coupling
crack pressure
cracks form
numerical analysis
