考虑超临界CO_(2)损伤的椭球形三维裂缝计算新模型

A new 3D model for calculating ellipsoidal fractures considering damage from supercritical CO_(2)

目前超临界CO_(2)压裂研究成果多集中于室内岩石损伤机理和劣化力学参数测试,对压裂形成的三维裂缝形态研究较少。为刻画超临界CO_(2)压裂过程的裂缝形态展布,基于Griffith断裂力学理论,建立了平面应变条件下椭球形裂缝扩展的三维计算新模型;结合前人室内测试结果,回归了岩石弹性力学参数与超临界CO_(2)多浸泡因素关联式,讨论了超临界CO_(2)压力、温度、施工排量、初始弹性模量、初始泊松比、缝内净压力、储层厚度等参数对裂缝扩展形态的影响。结果表明:针对上下存在水层的目的层采用超临界CO_(2)压裂时更应采取控缝高的措施;针对低渗储层,可优先考虑超临界CO_(2)压裂;超临界CO_(2)压裂工艺更适用于最小水平主应力大的储层;超临界CO_(2)压裂时,有助于低排量下获得相同的平均缝宽。研究成果对非常规油气水平井超临界CO_(2)压裂裂缝参数优化具有重要意义。

Most current research on supercritical CO_(2)fracturing focuses on laboratory test of rock damage mechanism and deterioration mechanical parameters,while less on fracturing-formed 3D fractures geometry.In order to characterize fractures geometry extension during supercritical CO_(2)fracturing process,a new 3D calculation model for ellipsoidal fractures propagation in plane strain condition is established based on Griffith fracture mechanics theory.Combined with previous laboratory test results,a correlation equation between rock elastic mechanical parameters and supercritical CO_(2)multi-soaking factors is regressed.The influence of parameters of supercritical CO_(2)pres‑sure,temperature,pumping displacement,initial elastic modulus,initial Poisson’s ratio,net pressure in fractures,and reservoir thickness on fractures propagation geometry is discussed.The results show that,fracture heightcontrolled measures should be taken during supercritical CO_(2)fracturing for target layers with upper and lower aquifers,supercritical CO_(2)fracturing can be given prior consideration for hard and low-permeability reservoirs,supercritical CO_(2)fracturing technique is more suitable for reservoirs with high minimum horizontal principal stress,and supercritical CO_(2)fracturing helps to achieve the same average fracture width at low pumping displacement.The research results have much significance for fractures parameters optimization of supercritical CO_(2)fracturing in unconventional oil and gas horizontal wells.