滑套固井压裂起裂压力及影响因素

Fracture initiation pressure and its influencing factors during sliding sleeve fracturing in cemented wells

关键词:  固井  滑套固井压裂  起裂压力  水泥环  水平地应力差  端口方位角

Key words:  well cementing  sliding sleeve fracturing  fracture initiation pressure  cement sheath  horizontal stress difference  azimuth of valve

摘要:

起裂压力高是滑套固井压裂面临的主要问题。根据滑套固井压裂的特征,建立地应力条件下滑套固井压裂计算模型,运用有限元法及岩石抗拉强度准则计算起裂压力,通过长庆油田桃X井的实例进行验证。结果表明:水平地应力差及端口方位角是滑套固井压裂起裂压力的主要影响因素,随着水平地应力差的增大,起裂压力降低,端口方位角增大时,起裂压力增大;地层岩石的弹性模量对起裂压力有较大影响,随着地层岩石弹性模量的增大,起裂压力增大;水泥环厚度对起裂压力的影响规律与水泥环和地层的弹性模量有关,当地层弹性模量大于水泥环弹性模量时,起裂压力随水泥环厚度的增大而减小,当地层弹性模量小于水泥环弹性模量时,起裂压力随水泥环厚度的增大而增大。

Abstract:

The oilfield practice has indicated that high fracture initiation pressure is the main problem for applying sliding sleeve fracturing technique in cemented wells. A 3D model coupled with hydraulics and solid mechanics was established to study the characteristics of the sliding sleeve fracturing in cemented wells. The fracture initiation pressure was calculated using a finite element method and rock tensile strength criteria. A case study of Tao-X well in Changqing Oilfield was conducted to verify the model, and the influence factors of fracture initiation pressure were analyzed. The results indicate that horizontal stress difference and azimuth of valve are the main influence factors to the fracture initiation pressure. The fracture initiation pressure decreases with the increase of the horizontal stress difference and increases with the increase of the azimuth of valve. The elastic modulus of the rock formation also has a significant effect on the fracture initiation pressure, the higher the elastic modulus, the greater the fracture initiation pressure needed. The effect of cement sheath on fracture initiation pressure is related to the elastic modulus of the cement and rock formation. The fracture initiation pressure increases with the increase of the thickness of cement sheath when the elastic modulus of the cement is bigger than that of the rock formation, and vice versa.