基于反常扩散模型的页岩气藏压裂水平井产能研究

摘要/Abstract

摘要：

页岩气藏体积压裂后,由于气体渗流孔隙尺度的突变以及基质与裂缝性质的显著差异,使渗流速度场表现出急剧的不连续性,致使连续介质假设条件不成立。为清楚认识页岩气藏渗流规律并进行产能研究,基于页岩气压裂水平井三线性流模型,耦合分形多孔介质的反常扩散方程,建立页岩气压裂水平井产能模型,运用Laplace变换和Stehfest数值反演得到无因次产量,结合实例计算分析并绘制出无因次产量递减曲线。研究结果表明：页岩气流动阶段分为人工裂缝线性流阶段、人工裂缝和天然裂缝双线性流阶段、天然裂缝线性流阶段、天然裂缝和基质双线性流阶段、基质线性流阶段;基于所建立的产能模型,研究了反常扩散指数、拟渗透率、储容比、裂缝间距等对产能的影响;结果表明：反常扩散指数越小,基质的非均质性越强,生产后期产能递减越明显;天然裂缝拟渗透率主要影响天然裂缝线性流期时间长短,而人工裂缝拟渗透率对页岩气藏的影响覆盖了生产周期的中后期;弹性储容比越大,产能的增加幅度越明显。研究为页岩气藏产能分析及评价提供了一个新的思路及方法。

关键词: 页岩气, 反常扩散, 体积压裂, 天然裂缝, 产能, Laplace变换

Abstract:

After the volume fracturing of shale gas reservoirs, due to the abrupt variations in the pore scale of the gas seepage and the severe difference between the characteristics of shale matrix and fractures, the seepage velocity field showed a sharp discontinuity, resulting in the failure of continuum assumption. In order to accurately understand the flow pattern of shale gas reservoirs and analyze the productivity, based on the trilinear flow model of fractured horizontal wells in shale gas reservoirs and coupled with the anomalous diffusion equation of fractal porous media, we established a fractured horizontal well productivity model of shale gas reservoirs. The dimensionless production was obtained by Laplace transform and Stehfest numerical inversion. Finally, we analyzed its result combining specific example and obtained a dimensional production curve. The analysis results showed that five flow regions for shale gas could be identified, including the linear flow stage of hydraulic fractures, the bilinear flow in hydraulic fractures and natural fractures, the linear flow stage of natural fractures, the bilinear flow in natural fractures and matrices, and the phase of matrix linear flow. Based on the production model, we also studied the influence of anomalous diffusion exponent, pseudo-permeability, storability ratio, fracture spacing and the like. on the production of shale gas reservoirs. The results indicated that the smaller abnormal diffusion exponent and the stronger matrix heterogeneity were, the more obvious decrease of productivity would be, and the natural fractures pseudo-permeability had great impact on the length of time in the linear flow of the natural fractures. Furthermore, the hydraulic fracture pseudo-permeability could influence the productivity in the whole middle-late production cycle. The larger the storability ratio was, the more obvious increase amplitude of productivity would be. The research provided a new idea and method for productivity analysis and evaluation of shale gas reservoirs.

Key words: shale gas, anomalous diffusion, volume fracturing, natural fractures, productivity, Laplace transform

中图分类号:

TE312

李勇明,吴磊,陈希. 基于反常扩散模型的页岩气藏压裂水平井产能研究[J]. 油气藏评价与开发, 2019, 9(1): 72-79.

Yongming Li,Lei Wu,Xi Chen. Research on productivity of fractured horizontal wells in shale gas reservoirs based on anomalous diffusion model[J]. Reservoir Evaluation and Development, 2019, 9(1): 72-79.

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