Keyvani Fatemeh, Safaei Ali, Kazemzadeh Yousef, Riazi Masoud, Qajar Jafar
Department of Petroleum Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, 7193616511, Iran.
Fouman Faculty of Engineering, College of Engineering, University of Tehran, Tehran, 4358139115, Iran.
Sci Rep. 2024 Jun 11;14(1):13405. doi: 10.1038/s41598-024-64194-2.
Miscible gas injection in tight/shale oil reservoirs presents a complex problem due to various factors, including the presence of a large number of nanopores in the rock structure and asphaltene and heavy components in crude oil. This method performs best when the gas injection pressure exceeds the minimum miscibility pressure (MMP). Accordingly, accurate calculation of the MMP is of special importance. A critical issue that needs to be considered is that the phase behavior of the fluid in confined nanopores is substantially different from that of conventional reservoirs. The confinement effect may significantly affect fluid properties, flow, and transport phenomena characteristics in pore space, e.g., considerably changing the critical properties and enhancing fluid adsorption on the pore wall. In this study, we have investigated the MMP between an asphaltenic crude oil and enriched natural gas using Peng-Robinson (PR) and cubic-plus-association (CPA) equations of state (EoSs) by considering the effect of confinement, adsorption, the shift of critical properties, and the presence of asphaltene. According to the best of our knowledge, this is the first time a model has been developed considering all these factors for use in porous media. We used the vanishing interfacial tension (VIT) method and slim tube test data to calculate the MMP and examined the effects of pore radius, type/composition of injected gas, and asphaltene type on the computed MMP. The results showed that the MMP increased with an increasing radius of up to 100 nm and then remained almost constant. This is while the gas enrichment reduced the MMP. Asphaltene presence changed the trend of IFT reduction and delayed the miscibility achievement so that it was about 61% different from the model without the asphaltene precipitation effect. However, the type of asphaltene had little impact on the MMP, and the controlling factor was the amount of asphaltene in the oil. Moreover, although cubic EoSs are particularly popular for their simplicity and accuracy in predicting the behavior of hydrocarbon fluids, the CPA EoS is more accurate for asphaltenic oils, especially when the operating pressure is within the asphaltene precipitation range.
由于多种因素，包括岩石结构中大量纳米孔的存在以及原油中的沥青质和重组分，在致密/页岩油藏中进行混相气体注入是一个复杂的问题。当注入气体压力超过最小混相压力（MMP）时，这种方法效果最佳。因此，准确计算MMP尤为重要。一个需要考虑的关键问题是，受限纳米孔中流体的相行为与常规油藏中的相行为有很大不同。限域效应可能会显著影响孔隙空间中流体的性质、流动和传输现象特征，例如，极大地改变临界性质并增强流体在孔壁上的吸附。在本研究中，我们通过考虑限域、吸附、临界性质的变化以及沥青质的存在，使用彭 - 罗宾逊（PR）和立方加缔合（CPA）状态方程（EoS）研究了含沥青质原油与富化天然气之间的MMP。据我们所知，这是首次开发出考虑所有这些因素用于多孔介质的模型。我们使用消失界面张力（VIT）方法和细管试验数据来计算MMP，并研究了孔隙半径、注入气体类型/组成以及沥青质类型对计算得到的MMP的影响。结果表明，MMP随着半径增加到100 nm而增大，然后几乎保持不变。与此同时，气体富化降低了MMP。沥青质的存在改变了界面张力降低的趋势并延迟了混相的实现，使得其与无沥青质沉淀效应的模型相差约61%。然而，沥青质类型对MMP影响很小，控制因素是油中沥青质的含量。此外，尽管立方EoS因其在预测烃类流体行为方面的简单性和准确性而特别受欢迎，但CPA EoS对于含沥青质的油更准确，尤其是当操作压力处于沥青质沉淀范围内时。
