页岩气扩散实验与数学模型

在地层条件下，页岩气流动状态受多尺度效应影响，包含黏性流、扩散流以及滑脱流等，气体的产出是多种机制协同作用的结果，前人提出的扩散模型已不能准确地描述页岩气在基质中的扩散行为。为了定量表征页岩气扩散能力的影响因素，揭示气井在全生命周期开发过程中的流动规律以及对产能的影响，利用自主研发的高温高压近平衡态实验系统,开展了页岩气在0~1 MPa微压差条件下的流动实验，并提出一种综合考虑渗透率、温度与压力的扩散系数计算方法，成功地运用于川南地区五峰组-龙马溪组页岩中，指出该地区优质储层扩散产量成为主控因素时临界开发压力为4.5 MPa，对于页岩气井产能评价以及扩散能力的表征有重要的意义。通过实验结果与理论分析表明，扩散在高温、低渗、低压力条件下会有更高的分配系数，考虑了基质渗流能力的扩散系数模型能更好地运用在实际流动中，忽略扩散的影响将对产能计算带来较大误差。

Diffusion experiment of shale gas and mathematical model

Under formation condition, the flow state of shale gas is affected by multi-scale effects, including viscous flow, diffusion flow and slippage flow, etc., gas production is the result of synergy of various mechanisms, and previous diffusion models can no longer accurately describe the diffusion behavior of shale gas in the shales. In order to clarify the influencing factors of shale gas diffusion ability, reveal the flow law of gas wells in the whole life cycle development process as well as the impact on production capacity, experiments on shale gas under the conditions of 0-1 MPa micro-pressure difference is carried out by using the self-developed experimental system with high temperature and high pressure resistance, and put forward a diffusion coefficient calculation method comprehensively considering permeability, temperature and pressure. It was successfully applied to the Wufeng-Longmaxi formations shale in the south of Sichuan, indicating that the critical pressure of the high-quality reservoir in this area is 4.5 MPa when diffusion flow occupy the main position. It is of great significance for the shale gas well productivity evaluation and the quantitative characterization of the diffusion capacity. The experimental results and theoretical analysis show that the diffusion will have a higher partition coefficient under high temperature, low permeability and low pressure level, the diffusion coefficient model considering the permeability of shales can be better applied in actual flow, and there will be a large error in productivity calculation if ignoring the effects of diffusion.