井筒协调条件下多裂缝的相继开启模型

STUDY ON THE CRAZING MODEL OF MULTIPLE-HYDRAULIC FRACTURES UNDER THE HARMONY OF THE PRESSURE IN THE WELLBORE

长期以来,人们认识到水力压裂过程中存在多裂缝现象,然而对于多条裂缝形成的机理认识不清。通过建立考虑裂缝延伸、井筒内流体压缩性的井口压力升高模型,模拟计算了井口压力升高的过程;同时考虑多条裂缝之间开启压力的差别,建立了多条裂缝相继开启的条件。分析表明,井口压力升高的机理是:由于井底流体不能很快扩散出去,因而在井筒内造成憋压;与此同时,流体在裂缝内流动的延伸阻力与射孔摩擦阻力一起与井底压力平衡。多个裂缝开启的条件是,井底压力的升高程度达到了次级裂缝的开启压力,其内在机理是井口液体的注入能力大于已经开启裂缝接纳液体的能力,多裂缝起裂指数Cm大于1。

With the increasing of the complexity of reservoirs, the phenomena of multiple-fractures have been congnized, but the mechanism has not been understood adequately. This paper simulated the increasing course of wellhead pressure through considering fracture prolongation and the compressible character of liquid. The rule of multiple-fractures crazing one after the other is established considering the difference of breaking pressure between multiple-fractures. The pressure buildup mechanism is the pressure holding back in the wellbore due to liquid can’t be diffused quickly in the bottom hole, and the resistance summation of liquid in the fracture and the perforation balance with the bottom hole pressure. The condition of multiple-fractures breaking one after another is that the bottom hole pressure is higher than the breaking pressure of the next pressure, which essence is that the injecting capability of liquid is bigger than admitting capability of the facture and the index of multiple-fractures breaking one after another exceeds 1.