复合射孔爆燃气体压裂裂缝起裂扩展研究

结合线弹性断裂力学的裂缝尖端应力强度因子判据,建立了复合射孔爆燃气体压裂裂缝的起裂扩展模型,通过建立与多个变量相关的缝内气体压力分布函数,利用迭代法实现了模型的数值求解,获得了缝内气体压力分布随时间的动态变化规律,并分析了不同特征参数对裂缝起裂扩展与止裂过程的影响。实例计算结果表明:(1)随着裂缝扩展的进行,爆燃气体流动尖端与裂缝尖端经历了由重合到不重合再到重合的过程;(2)地应力越大,裂缝起裂扩展越困难,爆燃气体有效致裂作用时间越短,最终得到的裂缝扩展长度也越小;(3)初始裂缝越长,裂缝更容易起裂扩展,爆燃气体能量利用率越高,裂缝扩展更长;(4)岩石断裂韧性的改变对裂缝起裂、止裂和裂缝扩展长度没有明显的影响;(5)升压速率越小,爆燃气体有效致裂作用时间越长,最终裂缝扩展也更长,但对裂缝起裂压力与止裂压力几乎没有影响。

Initiationandextensionofgas-drivenfractureduringcompoundperforation

Combinedwiththecracktipstressintensityfactorcriterionoflinearelasticfracturemechanics, themodelofinitiationandextensionofgas-drivenfracturesbycompoundperforationisestablished. Afunctionwithmultiplevariablesdescribinggaspressuredistributionincrackisproposed hereintorealizethenumericalresolutionofthemodelusingtheiterationmethod,andthedynamic changelawofgaspressuredistributioninfracturewithtimeisobtained.Inaddition,theeffectofdifferentcharacteristicparametersontheprocessoffractureinitiationandextensionaswellasfracture arrestisanalyzed.Theexamplecalculationshows:(1)withtheprogressoffractureextension,the leadingedgeoftheflowandthefracturetipwillexperiencetheprocessfromcoincidencetononcoincidenceandthentocoincidence;( 2)thefractureinitiationandextensionaremoredifficultasin-situ stressisgreater,whichmakestheeffectivetimeofgas-drivenandthefractureshorter;(3)thefractureinitiationandextensionareeasierandtheutilizationofgasenergyishigherastheinitialcrackis longer,resultinginthelongercrack;(4)thechangeoffracturetoughnesshasnoobviousinfluenceon thecrackinitiationandextensionaswellasthefracturearrest;(5)boththeeffectivetimeofgas-drivenandthefracturearelongerastherateofpressureriseissmaller, butitschangehasnearlynoimpactonthepressureofthefractureinitiationandarrest.