改进的页岩气五区复合产能模型及其影响因素

Shale gas improved five-zone composite productivity prediction model and its influencing factors

产能是评价页岩气田开发效果的核心指标,其中页岩气高压物性、超临界解吸、多重微观流动机理以及应力敏感性的综合非线性效应对产能的贡献程度不可忽略。由于前人提出的产能模型考虑的非线性影响较为单一,关于综合研究非线性因素对产能贡献的研究成果较少,因此基于常规五区复合线性流模型,耦合了气体的非线性效应和缝网应力敏感性,建立了改进的复合线性流模型并得到产能半解析解,通过实例验证产能解的可靠性和明确优化了影响产能的重要因素。结果表明:①该模型综合考虑气体产出过程中非线性效应对产量的影响,计算精度大幅提高,可合理评价预测气井中长期的产能大小;②裂缝半长越大,产能越大,应尽可能造长缝;主裂缝簇间距和导流能力过高或者过低,储层的动用程度变化不明显,主裂缝簇间距和导流能力取值可分别优选在10 m左右和4.0×10^(−15) m^(3)左右。应力敏感系数越大,产能越低,压裂过程应优选性能优良的支撑剂或设计裂缝面滑移以提高裂缝导流能力;③水平井巷道间距和水平段长度对于提高储层动用程度效果是可观的,在实际生产中巷道间距可优选500 m,同时建议可适量部署长度2000~3000 m的水平井进行技术攻关。研究成果可紧密联系现场开发,合理评价预测产能及指导优化压裂设计参数以最大限度提高页岩气采收率,具备一定的理论意义和工程价值。

Productivity is the core index to evaluate the development effect of shale gas field,and the compre⁃hensive nonlinear effect of high-pressure physical property,supercritical desorption,multiple micro-flow mecha⁃nism and stress sensitivity of shale gas can’t be ignored in its contribution to productivity.In this paper,based on the conventional five-zone compound flow model,a comprehensive consideration was given to gas nonlinearity and the stress sensitivity,an improved compound linear flow model was established and a semi-analytical solution for productivity was obtained.Then,the reliability of productivity solution was verified through examples and important influencing factors were clarified.The results indicated:(1)The model comprehensively consid⁃ers the impact of nonlinear effects on gas production so as to predict the medium-and long-term productivity of gas wells accurately.(2)The greater the main fracture half-length,the greater the productivity,so long frac⁃tures should be designed as much as possible;too high or too low the cluster spacing and conductivity of the main fractures do not significantly change the extent of reservoir utilization,so the values of the cluster spacing and conductivity of the main fractures in this paper can be preferably around 10 m and around 4.0×10^(−15) m^(3);the greater the stress sensitivity coefficient,the lower the productivity,and the proppant with excellent performance should be selected or the fracture slip surface should be designed to improve the fracture conductivity.(3)The significance of horizontal well spacing and horizontal well length on improving the utilization of shale reservoirs is considerable.In actual production,the horizontal well spacing can be optimized to 500 m,and horizontal well length of 2000-3000 m can also be adopted for technical research.