裂缝对气藏储层渗透率及气井产能的贡献

Experimental study on fracture contribution to gas reservoir permeability and well capacity

裂缝是气藏储层渗流的重要通道,对储层渗透率的贡献十分明显,但目前难以量化评价。针对这一难题,综合考虑裂缝尺度(缝高、缝宽和裂缝贯通程度),通过对岩心进行人工定量造缝后开展气测渗透率实验测试,分别研究了贯通和非贯通(贯通程度分别为20%,40%,60%,80%)2种情景下裂缝对岩石渗透率的贡献。结果表明,贯通和非贯通裂缝对地层岩石渗透率均有贡献。贯通裂缝对岩心渗透率贡献十分明显,可提高岩石渗透率80%以上,其作用大小与裂缝开度(缝高×缝宽)密切相关;非贯通裂缝对岩石渗透率也存在一定的贡献,对基质起到沟通作用,改善储层整体的渗流能力,其作用大小与裂缝贯通程度关系密切。在实验测试的基础上,以单井为研究对象,综合考虑裂缝导流能力、裂缝沟通能力和基质供气能力三方面因素,建立了裂缝对气井产能贡献数学模型,结合气田实际气井的基础参数评价了裂缝对气井产能的贡献。

Fractures are an important channel for the seepage of reservoir gas.It has an evident contribution to reservoir permeability.However,it is currently difficult to quantitatively evaluate.To solve this problem,an experimental test of gas permeability was carried out after the artificial quantitative fracturing of core.Three factors such as fracture penetration degree,fracture length and width were considered.The contribution of fractures to rock permeability was investigated under two conditions,one where fractures completely penetrate through the rock matrix,and the other in which fractures incompletely penetrate through the rock matrix with penetration degrees of 20%,40%,60%and 80%.Both types of fractures contribute to rock permeability.The penetrating fractures increase rock permeability by more than 80%,which is closely related to fracture opening degree(length×width).The nonpenetrating fractures also contribute to rock permeability,by communicating with the matrix and improving reservoir flow.Based on experimental tests,a mathematical model of fracture contribution to single gas well production capacity was established combining three factors:fracture conductivity,fracture communication and matrix gas supply capacity.The fracture contribution to gas well production capacity was estimated using this model together with the basic parameters of actual gas wells.