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可以以相对低的成本大量快速生产，并且最近已经彻底改变了石油和天然气工业。通常情况下，只有3%至7%的石油储量可以通过现有技术开采。页岩油地层中的油含量包括无机孔隙中所含的游离油和称为油母质的有机材料中的截留油。后者可以代表总石油的很大一部分，并且我们关于如何回收它的知识非常少，然而页岩油的生产目前仅针对油母岩中的游离油而不是截留的油。页岩油储层还具有通过将CO2溶解在油母质中来储存CO2的相当大的能力。缺乏提高页岩油采收率的方法促使我们对CO2和干酪根的物理相互作用进行同时的实验和理论研究。 在这项研究计划中，我们将开发几种新的实验方法来分析干酪根的岩石物理性质，以发现干酪根中捕获了多少油，如何使用CO2回收它们，以及在CO2注入页岩油回收后，页岩油储层中可以储存多少CO2。我们的初步研究结果表明，在将CO2注入页岩油储层期间，由于CO2与干酪根分子的强亲和力和相互作用，CO2可以渗透到干酪根基质中，同时将油从干酪根分子之间的空间排出。我们将通过实验来验证这一假设，并找到这一过程的机制。在干酪根中用CO2驱油的这种类型以前没有研究过。我们假设，这一过程可以消耗页岩油中的有机油饱和度的CO2注入，从而实现不仅采油，但CO2封存。 本研究的目的是开发最有效的CO2提高页岩油采收率和封存工艺。CO2-油逆流驱替机理的成功应用可使页岩油采收率提高15%~ 20%。这意味着可开采的页岩油可以增加一倍甚至两倍。该研究成果也适用于煤层气和页岩气地层中的CO2强化气体回收和封存。

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.