Experimental evaluation of live oil oxidation together with its physical properties during air injection in a tight oil reservoir

In this paper, an integrated and pragmatic framework has been developed to experimentally determine the live oil oxidation with its physical properties and evaluate performance of air injection in a tight reservoir. In addition to continuously measuring interfacial tension, slim tube tests were performed to monitor and quantify miscibility between air and live oil collected from the Upper Triassic Yanchang Formation of the Chang 7 tight oil reservoir in the Ordos Basin, China. The displacement experiments showed that oil recovery factor of air injection is obviously higher than that of nitrogen injection in core plugs collected from the tight oil reservoir, while static and dynamic oxidation experiments were then conducted to identify the inherent oxidation mechanisms. The comparative core displacement experiments of live oil by air and nitrogen injection under reservoir temperature and pressure were carried out to evaluate the enhanced oil recovery (EOR) performance of air injection. It is found that heat released by the oxygen addition reaction under the formation conditions of 60.0 degrees C and 16.00 MPa leads to the bond scission reaction. The gas generated by the bond scission reaction forms a flue gas displacement front together with the remaining nitrogen contained in the air. Although miscibility cannot be achieved, air injection followed by the oxygen addition reaction and the bond scission reaction can reduce oil viscosity and thus increase its flowability. As for the commonly experimental studies with dead oils excluding porous media, the oxidation degree and the corresponding physical properties are normally overestimated since light components are limited in the dead oils and porous media constrain the corresponding oxidation.

本文建立了一个综合实用的框架，用于通过实验确定含气原油的氧化及其物理性质，并评估致密油藏注空气的效果。除了连续测量界面张力外，还进行了细管实验，以监测和量化从中国鄂尔多斯盆地长7致密油藏上三叠统延长组采集的空气与含气原油之间的混相情况。驱替实验表明，在从该致密油藏采集的岩心塞中，注空气的采收率明显高于注氮气的采收率，随后进行了静态和动态氧化实验以确定内在的氧化机理。在油藏温度和压力条件下，进行了注空气和注氮气对含气原油的对比岩心驱替实验，以评估注空气提高采收率（EOR）的效果。研究发现，在60.0℃和16.00 MPa的地层条件下，加氧反应释放的热量导致键断裂反应。键断裂反应产生的气体与空气中剩余的氮气一起形成烟道气驱替前缘。尽管无法实现混相，但注空气后发生的加氧反应和键断裂反应可以降低原油粘度，从而提高其流动性。对于通常使用不包含多孔介质的脱气原油进行的实验研究，由于脱气原油中轻组分有限且多孔介质限制了相应的氧化，氧化程度和相应的物理性质通常被高估。