Investigating the mechanics of two-phase flow in rock fractures and caprocks

日益严重的全球变暖威胁正在推动在盐水层和枯竭的石油和天然气储层中封存二氧化碳的需求。CO2侵入储层孔隙空间的能力受多相流动力学的控制，因为它必须流入含有天然地下水的孔隙，在某些情况下，还含有碳氢化合物。在由裂缝岩石组成的储层中，大部分流动通过天然裂缝网络发生。虽然裂缝岩石中单相流动的力学已经得到了相当好的理解，但关于裂缝内两相流动的力学还存在相当大的不确定性。为了使任何储层长期保留CO2，它必须被细粒盖层覆盖，以防止CO2向上迁移。CO2只有在其压力超过这些孔喉中的毛细管压力时才能侵入盖层孔喉。因此，盖层孔隙网络的几何形状对发生CO2突破的压力具有关键影响。用CO2进行气体突破试验以及将盖层孔隙结构与突破压力相关联的经验有限。所提议的研究的短期目标是（1）测量盖层和裂缝储集岩中的两相流，以及（2）识别和量化控制它们的参数。长期目标是开发方法（1）快速和可靠地识别良好的盖层，（2）最大限度地提高裂缝性储层的储存能力。这项研究将使用研究人员的岩石力学实验室进行，辅以新的设备和技术，如同步显微镜在萨斯卡通的加拿大光源，和一个专门建造的裂缝流动可视化细胞。这项研究对社会的好处将是减少温室气体排放。经济效益将包括从用于二氧化碳储存的老化油藏中提高石油采收率，以及可能的碳信用交易，如京都议定书等国际协议。

The growing threat of global warming is driving the need to sequester CO2 in saline aquifers and depleted oil and gas reservoirs. CO2's ability to invade reservoir pore space is governed by multi-phase flow mechanics, as it must flow into pores containing native groundwater and, in some cases, hydrocarbons. In reservoirs consisting of fractured rocks, most of the flow occurs through a network of natural fractures. While the mechanics of single-phase flow in fractured rocks are reasonably well understood, there is considerable uncertainly regarding the mechanics of two-phase flow within fractures. In order for any reservoir to retain CO2 for long periods of time, it must be overlain by fine-grained caprocks that prevent the upwards migration of CO2. CO2 cannot invade caprock pore throats until its pressure exceeds the capillary pressures in these throats. As such, the geometry of the caprock pore network has a critical impact on the pressure at which CO2 breakthrough will occur. There is limited experience conducting gas breakthrough tests with CO2, and in correlating caprock pore structure to breakthrough pressure. The short-term objectives of the proposed research are (1) to measure two-phase flows in caprocks and fractured reservoir rocks, and (2) to identify and quantify the parameters that control them. The long-term objectives are to develop methods for (1) quickly and confidently identifying good caprocks, and (2) maximizing the storage capacity of fractured reservoirs. This research will be conducted using the researcher's Rock Mechanics laboratory, supplemented by novel equipment and techniques such as the synchroton microscope at Saskatoon's Canadian Light Source, and a purpose-built fracture flow visualization cell. The benefit of this research to society will be a reduction in greenhouse gas emissions. Economic benefits will include enhanced recovery of oil from aging reservoirs that are used for CO2 storage, and possibly the trading of carbon credits as governed by international agreements such as the Kyoto protocol.