Wetzel Maria, Kempka Thomas, Kühn Michael
German Research Centre for Geosciences, Fluid Systems Modelling, Telegrafenberg, 14473 Potsdam, Germany.
Institute of Geosciences, University of Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany.
Materials (Basel). 2020 Jul 11;13(14):3100. doi: 10.3390/ma13143100.
Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny-Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.
地球化学过程会改变岩石的微观结构，从而影响其在宏观尺度上的物理行为。通过将沉淀与局部流速大小相关联，利用典型储层砂岩的微计算机断层扫描（micro-CT）对三种空间变化模式对孔隙形态、渗透率和弹性模量的影响进行了数值研究。结果表明，矿物生长的位置对渗透率降低的影响很大，变化幅度可达四个数量级。高流速区域的沉淀特征是孔隙喉道主要堵塞，渗透率急剧降低，这可以用指数为20的幂律关系大致描述。均匀矿物生长对孔隙结构的持续改变会使渗透率降低，其程度与指数为4的幂律或科曾尼-卡曼关系相当。低流速区域的优先沉淀主要影响较小的喉道和孔隙，对流动状态影响较小，其渗透率降低幅度远低于指数为2的幂律计算值。尽管它们对水力学的影响完全不同，但空间沉淀模式对岩石弹性性质增加的影响仅略有不同，所研究的不同情况之间的差异高达6.3%。因此，充分表征空间沉淀模式对于量化岩石水力性质的变化至关重要，而本研究表明其对岩石弹性参数的影响是有限的。计算得到的孔隙度与渗透率以及弹性模量之间的关系可用于将微观尺度的研究结果放大到储层尺度模型，以提高其预测能力，这对于地质地下层的可持续利用至关重要。
