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迅速大量生产，最近给石油和天然气行业带来了革命性的变化。通常情况下，使用目前的技术，只有3%到7%的原地石油是可开采的。页岩油层中的含油量包括无机孔隙中的游离油和被称为干酪根的有机物质中的圈闭油。后者可能占总石油的很大一部分，我们对如何回收它的了解非常少，但页岩油目前的目标只是游离油，而不是干酪根中捕获的油。页岩油藏通过将二氧化碳溶解在干酪根中，也有很大的储存二氧化碳的能力。由于缺乏提高页岩油藏采收率的方法，促使我们对CO2与干酪根的物理相互作用进行了同步的实验和理论研究。*在这个研究计划中，我们将发展几种新的实验方法来分析干酪根的岩石物理性质，以找出有多少油被困在干酪根中，如何利用CO2进行开采，以及在注入CO2后页岩油藏中可以储存多少CO2以用于页岩油开采。我们的初步结果表明，在将CO2注入页岩油藏过程中，由于CO2与干酪根分子具有很强的亲和力和相互作用，CO2可以渗透到干酪根基质中，同时将石油从干酪根分子之间的空间中排出。我们将通过实验验证这一假说，并找出这一过程的机制。干酪根中二氧化碳驱油的这种类型以前没有被研究过。我们假设，这一过程可以通过注入CO2的方式来耗尽页岩油中的有机油饱和度，从而既实现了采油，又实现了CO2封存。*这项研究的目的是为页岩油藏开发最有效的二氧化碳强化采油和封存工艺。成功应用所提出的CO2-油逆流驱油机理，可额外获得15%~20%的现场页岩油采收率。这意味着可采页岩油可增加一倍甚至两倍。本研究成果也适用于煤层气和页岩气地层的CO2强化采气和封存。

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.******