Physical Interaction of Supercritical CO2 and Kerogen in Shale Oil Reservoirs for Enhanced Oil Recovery and CO2 Sequestration

页岩油资源已被证明能够以相对较低的成本大量快速开采，并在最近彻底改变了石油和天然气行业。一般来说，使用现有技术，只有3%到7%的石油是可开采的。页岩油层的含油量包括无机孔隙中的游离油和干酪根中有机物质中的圈闭油。后者占总石油的很大一部分，而我们对如何开采页岩油的了解却很少，然而目前页岩油的生产只针对游离油，而不是干酪根中被困的油。页岩油储层还具有通过将二氧化碳溶解在干酪根中来储存二氧化碳的巨大能力。页岩油藏提高采收率方法的缺乏促使我们对CO2与干酪根的物理相互作用进行实验和理论同步研究。

Shale oil resources have proven to be quickly producible in large quantities at relatively low cost, and have recently revolutionized the oil and gas industry. Typically, only 3 to 7% of the oil-in-place is recoverable by using current technologies. The oil content in a shale oil formation includes free oil contained in inorganic pores and trapped oil in the organic material called kerogen. The latter can represent a significant portion of the total oil and our knowledge on how to recover it is very little, yet production of shale oil currently targets only the free oil rather than the trapped oil in kerogen. Shale oil reservoirs also have a substantial capacity to store CO2 by dissolving it in kerogen. The lack of methods to enhance oil recovery from shale oil reservoirs motivates us to conduct a simultaneous experimental and theoretical study on the physical interaction of CO2 and kerogen. In this research program, we will develop several new experimental methods to analyse the petrophysical properties of kerogen to find how much oil is trapped in kerogen, how they can be recovered by using CO2, and how much CO2 can be stored in shale oil reservoirs after CO2 injection for shale oil recovery. Our preliminary results have shown that, during CO2 injection into a shale oil reservoir, CO2 can penetrate into the kerogen matrix due to a strong affinity and interaction of CO2 with kerogen molecules, and simultaneously expels oil from spaces between kerogen molecules. We will experimentally test this hypothesis and find the mechanisms of the process. This type of displacement of oil by CO2 in kerogen has not been studied before. We hypothesize that this process can deplete the organic oil saturation in shale oil by means of CO2 injection, thereby achieving not only oil recovery but also CO2 sequestration. The objective of this research is to develop the most effective CO2 enhanced oil recovery and sequestration process for shale oil reservoirs. Successful application of the proposed CO2-oil counter-current displacement mechanism can get an additional 15% to 20% of shale oil recovered in field. This means that the recoverable shale oil can be doubled or even tripled. The outcomes of this research are also applicable to CO2 enhanced gas recovery and sequestration in coalbed methane and shale gas formations.