MODELING THE EFFECTS OF SALT PRECIPITATION & KINETIC MINERAL REACTION ON WELL INJECTIVITY DUE TO CARBON DIOXIDE INJECTION IN DEEP SALINE AQUIFERS

为了减少二氧化碳排放量和减轻相关的负面影响，二氧化碳封存已经成为一种长期有效减少二氧化碳排放的方法。在潜在的地质储存地点中，深层咸水层堆是最具吸引力的储存选择。然而，目前对于在这些咸水层中存在的二氧化碳、宿主岩层和原位盐水之间进行的复杂过程知之甚少。
一旦注入二氧化碳，在形成酸性环境的情况下，可能发生的矿物溶解和沉淀反应有可能改变岩层的特性。此外，由于盐水相向连续流动的干燥二氧化碳相的蒸发，可能导致盐析，这是一个在实验规模上已经广泛观察到的现象，并对样品的孔隙度和渗透率产生负面影响。
然而，这些地球化学矿物反应对于岩层特性和井注入能力在工业界仍存在争议，因此进行了一个矿场规模的模拟研究，以评估和量化其潜在的重要性。采用了商业模拟软件GEM来开发多个模型，以模拟对硅质深层咸水层的长期注入二氧化碳。观察了原位岩矿物溶解和沉淀以及注入二氧化碳后盐析的规模和范围，并评估了对井注入能力的影响。
还进行了敏感性研究，以评估二氧化碳注入速率、岩层温度和岩层盐度对盐矿物沉淀及其负面影响的潜在影响。此外，研究了通过淡水预冲洗来减轻盐析的负面影响的潜力。
在注入二氧化碳后，溶解被观察到是主要的矿物反应，然而溶解的范围有限，对井注能力的影响很小。盐析的范围仅限于井口附近区域，对井注能力的影响有限。地层矿化度是影响盐析的最重要特性，高矿化度会对岩层孔隙度和渗透性造成明显影响。然而，可以通过在二氧化碳注入开始前进行3个月的淡水注入期来有效消除这些影响。

Abstract

Within recent years public interest has steadily been growing over global climate change and the lasting effects caused by greenhouse gas emissions, carbon dioxide in particular. In attempting to reduce CO2 emissions and mitigate the associated negative effects, carbon dioxide capture and storage, also known as carbon dioxide sequestration, has emerged as a method by which CO2 emissions may effectively be reduced long term. Of the potential geologic storage sites for captured CO2, deep saline aquifers present the most attractive storage option.
Unfortunately, little is known about the complex processes which take place between CO2, the host formation, and in situ brine at the conditions found within these aquifers. Mineral dissolution and precipitation reactions which take place in response to the acidic environment formed once CO2 is injected have the potential to alter formation properties. In addition, Halite precipitation due to vaporization of the brine phase into the continuous flowing dry CO2 phase is a phenomenon which has been observed extensively on the experimental scale and has been observed to negatively impact sample porosity and permeability.
The impacts of these geochemical mineral reactions on formation properties and well injectivity on the field scale is however debated within industry and thus a field scale simulation study was performed in order to evaluate and quantify the potential significance. The commercial compositional reservoir simulation package GEM was used to develop multiple models in order to simulate prolonged CO2 injection into a siliciclastic deep saline aquifer formation. The scale and extent of host mineral dissolution and precipitation as well as halite mineral precipitation following CO2 injection were observed, and the impacts to well injectivity assessed. A sensitivity study was performed in order to assess the potential impacts of CO2 injection rate, formation temperature, and formation salinity on halite precipitation and its negative effects. In addition the potential for mitigation of the negative effects of halite precipitation through means of a fresh water pre flush was studied.
Following CO2 injection, dissolution was observed to be the predominant mineral reaction however the limited scale of dissolution resulted in minimal impact on well injectivity. The extent of halite precipitation was limited to the near well region with limited impacts on well injectivity. Formation salinity appears to be the most significant property in impacting halite precipitation with noticeable impacts to formation porosity and permeability at higher salinities. These effects can however be effectively negated with a 3 month fresh water injection period prior to the onset of CO2 injection.

Schematic showing CO2 injection into deep saline aquifer & pore scale view of salt precipitation in formation (Zhang, Moridis, and Pruess 2011)