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首页> 外文期刊>Transport in Porous Media >Effects of CO_2-Saturated Brine on the Injectivity and Integrity of Chalk Reservoirs
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Effects of CO_2-Saturated Brine on the Injectivity and Integrity of Chalk Reservoirs

机译：Co_2饱和盐水对粉笔储层的注射和完整性的影响

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Underground storage of CO2 in geological structures is very often accompanied by chemical interactions between the storage rock formation, existing fluids (e.g. brine) and injected CO2. Depending on the mineralogy and initial petrophysical properties of the rock formation, such reactions may also alter the petrophysical properties of the rock through dissolution, precipitation, fines migration and compaction mechanisms. In fact, carbonate formations are often highly reactive with carbonated brine and the extent of any reaction often depends on the precise rock composition as well as the accessible surface area with the fluid; a higher surface area will typically increase the reaction rate for heterogeneous systems between solids and liquids. Furthermore, fracturing and weakening of oil-bearing chalk reservoirs are approaches that have been implemented to improve oil recovery from various fields worldwide. In this paper, we present the results of an experimental study on a heterogeneous chalk sample (calcite concentration 98.9 wt%) which has been cut in half (to form an inlet and outlet sample) subjected to carbonated brine flooding under in situ reservoir conditions. The results show a significant increase in the post-flood permeability of the inlet plug and a slight decrease in the outlet plug. The increase in permeability of the inlet sample is supported by X-ray CT and SEM images which reveal significant mineral dissolution and establishment of preferential flow paths (or wormholes). On the other hand, dissolution is not observed in the outlet sample. This suggests that the fluid has reached equilibrium (i.e. achieved solute saturation) with the rock samples after traversing the first sample (i.e. there is no further mineral dissolution). This is strong evidence for the existence a dissolution front that forms during the core flooding process. With continued flooding of CO2-saturated brine, this front eventually traverses the whole sample and the dissolution becomes more substantial along the entire length of the core. As a result of the dissolution process, there is some degree of fines migration (induced by the dissolution in the first samples) into the outlet sample which has negative impacted its permeability. This change in permeability could also be caused by later precipitation of minerals from the brine, but this is likely a minor effect as the pore pressure/temperature conditions (for example, causing a pH change) do not vary significantly along the length of the samples. NMR T-2 distribution analysis shows reductions in the porosity and pore sizes are observed in both inlet and outlet plugs of the composite sample and these changes are likely due to a combination of compaction (caused by dissolution-induced weakening) and mineral dissolution/precipitation.
机译：地质结构的CO2的地下储存通常常伴在储存岩层，现有流体（例如盐水）和注射二氧化碳之间的化学相互作用。取决于岩石形成的矿物学和初始岩石物理性质，这种反应也可以通过溶解，沉淀，细粉迁移和压实机制来改变岩石的岩石物理性质。实际上，碳酸盐形成通常具有高反应性，与碳酸盐盐水，任何反应的程度通常都取决于精确的岩石组合物以及与流体的可接近的表面积;较高的表面积通常将增加固体和液体之间的异质系统的反应速率。此外，含油粉笔储层的压裂和弱化是已经实施的方法，以改善全球各种领域的石油回收。在本文中，我们介绍了在原位储层条件下被切割成的非均相白垩样品（方解石浓度> 98.9wt％）的实验研究的结果，该试样（以形成入口和出口样本） 。结果表明入口插头的泛洪水渗透率和出口插头略微减少的显着增加。入口样品的渗透率的增加由X射线CT和SEM图像支持，透露显着的矿物溶解和建立优先流动路径（或虫洞）。另一方面，在出口样品中未观察到溶解。这表明在穿过第一个样品（即没有进一步的矿物溶解）后，流体已达到平衡（即，实现溶饱和）与岩石样品。这是在核心洪水过程中存在的溶解前面存在的强有力证据。随着二氧化碳饱和盐水的持续洪水，该前部最终遍历整个样品，溶解沿芯的整个长度变得更加重要。由于溶解过程，存在一定程度的鳍片迁移（首先溶解在第一个样品中的溶解）进入出口样品，其具有负面影响其渗透性。这种渗透性的变化也可能是由盐水的后来沉淀的矿物质沉淀，但这可能是孔隙压力/温度条件（例如，导致pH变化）的微小效果不会沿样本的长度显着变化。 NMR T-2分布分析显示在复合样品的入口和出口塞中观察到孔隙率和孔隙尺寸的减少，并且这些变化可能是由于压实（由溶解引起的弱化引起的）和矿物溶解/沉淀的组合。

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