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

Abstract

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 °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.