富有机质页岩微孔中天然气自扩散耦合吸附与地质力学效应模拟

IF 4.9 2区 工程技术 Q2 ENERGY & FUELS
Clement Afagwu , Saad Alafnan , Mohamed Mahmoud , I. Yucel Akkutlu
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引用次数: 9

摘要

页岩地层中大量的天然气以溶解(吸收)相的形式存在于微孔和中孔中,以吸附(吸附)相的形式存在于相关的微裂缝表面。天然气在这种密闭空间中的输运主要受自扩散控制,这可以从克努森数中推断出来。自扩散受压力和空间约束的制约。在本研究中,形成了具有弯曲微孔和较大微裂缝的真实干酪根结构,并通过一些综合的分子模拟工作流程来评估页岩储层衰竭过程中的自扩散行为。输运模式分析表明,过渡自扩散是这些微孔中的主要输运机制。通过对吸附行为和力学性能的分析,建立了对孔隙压力和应力场变化敏感的过渡扩散模型。提出的模型与文献中的类似工作进行了比较和验证。结果表明,在一个典型的生产跨度内,压降会影响吸附剖面、孔隙的净覆盖应力和平均自由程,从而改变自扩散系数的大小。校正后的孔隙尺度模型具有较好的预测能力,相对误差为2.5-16%。深入讨论了结构弯曲度、吸附剖面和孔隙压力对有效扩散系数和气体解吸的影响。这项工作为研究真实干酪根几何结构中耦合多物理场过程对甲烷运移的影响提供了一种新的方法,可用于校准适合的孔隙尺度模型,用于大规模油藏模拟应用,并准确评估油藏动态和最终采收率。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Modeling of natural gas self-diffusion in the micro-pores of organic-rich shales coupling sorption and geomechanical effects

A significant amount of the natural gas in shale formations is contained in the micro- and mesopores as dissolved (absorbed) phase and on the surfaces of associated microcracks as (adsorbed) phase. The transport of natural gas in such confined spaces is primarily governed by self-diffusion as could be deduced from Knudsen number. Self-diffusion is governed by the pressure and the space confinement. In this study, realistic kerogen structures possessing both tortuous micropores and larger microcracks were formed and used to assess self-diffusion behavior during the depletion of shale reservoirs through some comprehensive molecular simulation workflow. Analysis of the transport modes revealed transition self-diffusion as the primary transport mechanism in these micropores. The sorption behavior and the mechanical properties were analyzed and incorporated to derive a transition diffusion model that is sensitive to changes in the pore pressure and the stress field. The proposed model was compared and validated against similar work in the literature. The results showed that during a typical production span, a pressure drop influences the sorption profile, the net overburden stress on the pores, and the mean free path, altering the magnitude of self-diffusivity. The calibrated pore scale model produced decent predictive ability with a relative error of 2.5–16%. The implications of structure tortuosity, sorption profile, and pore pressure on the effective diffusion coefficient and gas desorption are discussed in depth. This work provides a novel methodology for studying the effect of coupled multiphysics processes on methane transport in a realistic kerogen geometry, which could be used to calibrate a suitable pore scale model for upscaled reservoir simulation applications and accurate assessment of reservoir dynamics and ultimate recovery.

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来源期刊
Journal of Natural Gas Science and Engineering
Journal of Natural Gas Science and Engineering ENERGY & FUELS-ENGINEERING, CHEMICAL
CiteScore
8.90
自引率
0.00%
发文量
388
审稿时长
3.6 months
期刊介绍: The objective of the Journal of Natural Gas Science & Engineering is to bridge the gap between the engineering and the science of natural gas by publishing explicitly written articles intelligible to scientists and engineers working in any field of natural gas science and engineering from the reservoir to the market. An attempt is made in all issues to balance the subject matter and to appeal to a broad readership. The Journal of Natural Gas Science & Engineering covers the fields of natural gas exploration, production, processing and transmission in its broadest possible sense. Topics include: origin and accumulation of natural gas; natural gas geochemistry; gas-reservoir engineering; well logging, testing and evaluation; mathematical modelling; enhanced gas recovery; thermodynamics and phase behaviour, gas-reservoir modelling and simulation; natural gas production engineering; primary and enhanced production from unconventional gas resources, subsurface issues related to coalbed methane, tight gas, shale gas, and hydrate production, formation evaluation; exploration methods, multiphase flow and flow assurance issues, novel processing (e.g., subsea) techniques, raw gas transmission methods, gas processing/LNG technologies, sales gas transmission and storage. The Journal of Natural Gas Science & Engineering will also focus on economical, environmental, management and safety issues related to natural gas production, processing and transportation.
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