Experimental investigation on continuous N2 injection to improve light oil recovery in multi-wells fractured-cavity unit

The purpose of this experimental study is to evaluate the feasibility and oil recovery efficiency of continuous N2 injection in a multi-well fractured-cavity reservoir. In this study, the similar criterion of physical simulation was firstly discussed. In order to reveal the mechanism of remaining oil startup and production performance characteristic by continuous N2 injection, a visualized two-dimensional fractured-cavity model and a three-dimensional pressure resistant model were designed and fabricated respectively based on the similar theory. And the 2D visualized physical experiments and 3D physical experiments were performed with the simulated oil and brine reservoir samples in Tahe oilfield. Four groups of experiments in 2D and 3D model were performed, each of which included bottom water depletion driving, water injection and N2 injection. The 2D visualized experiments indicated the main mechanism of N2 developing remaining oil was to occupy the high position and replace the attic oil due to gravitational differentiation. Furthermore, both the 2D and 3D experiments demonstrated that higher oil recovery factor could be achieved if N2 was injected through high positional wells. The 3D physical model is closer to the real reservoir condition, so the production performance can reflect the real field production process. This paper confirmed the efficiency of continuous N2 flooding in the light oil saturated fractured-cavity reservoir.