CO2提高页岩油采收率及埋存机理

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 analyze the petrophysical properties of kerogen to find how and 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 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.

页岩油具有良好的勘探开发前景。而在现有技术条件下，页岩油的可动储量仅为3%～7%。页岩油主要以游离态赋存于无机孔隙和以吸附互溶态赋存于有机质中，后者相比于前者更加难以动用。高效开发页岩油及最大限度的利用有机质贮存CO2的关键在于有效动用吸附互溶态页岩油，但缺乏有效的开发方法，故亟待开展页岩油增产方法和机理研究。本课题通过建立全新的实验方法表征干酪根中流体的储集性能，探究CO2驱替吸附互溶态页岩油的机理及其在干酪根中的埋存能力。初步的结果表明，CO2与干酪根具有强相互作用，可溶解于干酪根中，并将其中的烃类流体驱替出来，大大提高页岩油采收率。本课题首次提出了CO2与干酪根中烃类流体的反向扩散驱替机理。在CO2驱替页岩油的过程中，CO2进入了干酪根中，既达到了提高采收率的效果，又实现了CO2埋存的目的。这一研究成果对煤层气和页岩气的开发具有借鉴意义。

页岩油具有良好的勘探开发前景。而在现有技术条件下，页岩油的可动储量仅为3%～7%。.页岩油主要以游离态赋存于无机孔隙和以吸附互溶态赋存于有机质中，后者相比于前者更加难以动用。高效开发页岩油及最大限度的利用有机质贮存CO2的关键在于有效动用吸附互溶态页岩油，但缺乏有效的开发方法，故亟待开展页岩油增产方法和机理研究。本课题通过真空自吸实验方法表征了吸附互溶在干酪根中烃类流体的含量，研究了CO2和烷烃混合物在页岩中竞争吸附溶解规律，并利用分子动力学模拟揭示了CO2与烃类流体在干酪根中的反向扩散驱替机理。结果表明游离油、吸附油和溶解油在页岩中的赋存量分别与页岩孔隙度、比表面积和有机质量有关。CO2对吸附态烷烃的取代能力强于有机质中溶解态烷烃，只有当游离相CO2浓度超过阈值，CO2才能将溶解态烷烃取代。干酪根与CO2的相互作用能低于干酪根和烃分子的相互作用能，导致CO2和烃分子在干酪根中的反向扩散过程自发进行，从而实现了CO2置换干酪根中的吸附溶解油。CO2置换干酪根中烃分子的效率受压力、温度、烃分子种类和干酪根类型的影响。在CO2驱替页岩油的过程中，CO2进入了干酪根中，既达到了提高采收率的效果，又实现了CO2埋存的目的。这一研究成果对煤层气和页岩气的开发同样具有借鉴意义。