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

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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.