页岩气储层多级压裂水平井非线性渗流理论研究

发布时间：2018-09-19 12:47

【摘要】：页岩储集层纳米级孔喉直径为5～200nm,渗透率为1×10-9～1×10-3μm2,与常规储集层流体流动具有明显不同,页岩气在页岩中的流动不仅有渗流过程,还存在解吸、扩散、滑移流动,气体在低渗透及致密气藏孔隙喉道中流动规律也不适用于页岩气藏。为此,本文将针对页岩气储层自生自储和纳微米孔隙尺度的特点,充分考虑多种流动机理,建立页岩气储层多尺度流动模型,并在此基础上形成页岩气储层多级压裂水平井非线性渗流理论。本文针对页岩气储层具有纳微米级孔隙流动特点,采用连续介质力学与分子运动学相结合的方法进行描述。根据努森数判断流体的流态,绘制了流态图版,阐明了不同区域的流动机理和流态特征,计算分析了渗透率校正因子随着努森数的变化关系。建立了考虑扩散、滑移特性的页岩气储层多尺度流动模型,并结合页岩渗流规律实验,进行对比验证。在此基础上推导出考虑解吸、扩散和滑移作用的非线性流动方程。考虑不同缝网形态,运用保角变换及等值渗流阻力方法建立了考虑扩散、滑移及解吸吸附作用的基质-裂缝耦合多尺度流动压裂井产能方程,并对页岩气压裂直井及多级压裂水平井产能影响因素进行了分析。考虑解吸吸附随压力及时间变化,基于质量守恒,建立了新的不稳定控制方程。由于缝网区域和基质区域渗透率等性质差别较大,引入复合区模型,一区为裂缝-缝网区,二区为基质区,建立模型并进行求解。建立了含连续微裂缝表面层基质-裂缝双重介质球形模型,通过Laplace变换和Stehfest数值反演,求解得到了水平井井底流压及压裂水平井产量曲线。数值计算结果表明：游离气产量占总产气量的85%-90%,对总产气量贡献较大。有机质孔隙内气体解吸使页岩气井产量递减减慢,解吸量越大,页岩气井产量越大,产量递减越慢,并对生产中、后期气体产能影响较大。通过对水平井缝网压裂模型的计算,随着产量的增加,地层压力下降越快,基质区的压力波传播边界最大为缝网区外150m。产量呈现“L型”曲线,生产初期产量下降速度较快。该模型具有很强的理论及工程应用性,为页岩气产能预测及开发指标优化提供了理论依据。
[Abstract]:The pore throat diameter and permeability of shale reservoir are 5 ~ 200nm and 1 脳 10 ~ (-9) ~ (-1) 脳 10 ~ (-3) 渭 m ~ (2) respectively. The flow of shale gas in shale is different from that of conventional reservoir fluid. The flow of shale gas in shale has not only percolation process, but also desorption, diffusion and slip flow. Gas flow in the pore throat of low permeability and tight gas reservoirs is also not suitable for shale gas reservoirs. In this paper, according to the characteristics of self-generation self-reservoir and nanometer-pore scale of shale gas reservoir, the multi-scale flow model of shale gas reservoir is established by fully considering various flow mechanisms. On this basis, the nonlinear seepage theory of multistage fracturing horizontal well in shale gas reservoir is formed. In this paper, according to the characteristics of pore flow in shale gas reservoir with nanometer-order, the method of combining continuum mechanics with molecular kinematics is used to describe the reservoir. According to the Knudsen number, the flow pattern is drawn, the flow mechanism and characteristics in different regions are explained, and the relation between the permeability correction factor and the Knudsen number is calculated and analyzed. A multi-scale flow model of shale gas reservoir considering diffusion and slip characteristics was established and compared with the experimental results of shale percolation law. On this basis, a nonlinear flow equation considering desorption, diffusion and slip is derived. Considering different fracturing patterns, the productivity equations of matrix fracture coupled multi-scale fluid fracturing wells with diffusion, slippage and desorption adsorption are established by using conformal transformation and equivalent seepage resistance method. The factors affecting the productivity of the straight and multistage fracturing horizontal wells are analyzed. Considering the change of desorption adsorption with pressure and time, a new unstable governing equation is established based on mass conservation. Due to the great difference in permeability between the fracture network area and the matrix area, the composite zone model is introduced. The first zone is the fissure-fracture zone, the second zone is the matrix area, and the model is established and solved. A spherical model with continuous microfracture surface layer matrix and fracture is established. By Laplace transform and Stehfest numerical inversion, the bottom hole flow pressure and the production curve of fractured horizontal well are obtained. The numerical results show that the free gas output accounts for 85-90% of the total gas production and contributes greatly to the total gas production. The gas desorption in the pores of organic matter slows down the production of shale gas wells, and the larger the desorption amount, the larger the production of shale gas wells and the slower the decline of production, which has a great influence on the gas productivity in the later stage of production. Through the calculation of fracture pattern fracturing model of horizontal wells, with the increase of production rate, the formation pressure decreases more quickly, and the maximum pressure wave propagation boundary in the matrix area is 150 m outside the fracture net area. The yield showed "L type" curve, and the yield decreased rapidly at the beginning of production. The model has strong theory and engineering application, which provides theoretical basis for shale gas productivity prediction and development index optimization.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE312

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