Investigation the Impact of Different Injection Agents on Tight Oil Reservoirs of Recovery Performance

Abstract Objectives/Scope: Due to strong water sensitivity and extremely low permeability, conventional water flooding method is not suitable for the Mahu Conglomerate reservoir. In response to the complex reservoir physical properties, different injection agents such as CO 2 , N 2 , water and air huff and puff injection were carried out in order to optimize injection parameters for enhanced oil recovery in tight conglomerate reservoirs. Methods, Procedures, Process: By means of NMR, scanning electron microscopy, energy spectrum, pore fluids state in different media after different agents displacement were studied. Displacement and CT testing on different media and post fracturing state were conducted. Through experiments on on-site cores from two different layers, three different injection media (H 2 O, N 2 , CO 2 and air with different O 2 concentration) were tested for enhanced oil recovery. Then, the injection process was performed under different injection pressures. Finally, multiple cycles of enhanced oil recovery tests were conducted corresponding optimal injection pressures. Results, Observations, Conclusions: The remaining oil in the pores is mainly in free and bound states, with a free state of approximately 58% and a bound state of approximately 42%. Four pressures were selected for this test based on the minimum miscibility pressure of CO 2 with crude oil: 15MPa, 20MPa, 23MPa, and 25MPa. The recovery factor under different pressures is 6.44%, 8.14%, 10.31%, and 10.38%, respectively. As the huff and puff pressure increases, the recovery of CO 2 huff and puff gradually increases, and the increase of recovery is insignificant when the mixture pressure is reached. The gas flooding process involves oil production from large and submicron pores first. As the displacement pressure difference increases, oil production from large pores decreases, with medium pores becoming the main force of oil production, while oil production from nanoscale micropores shows an increasing trend. The increase in oxygen content results in significant development of sub-micron micron scale pores. The gas breakthrough time is long, the capillary force decreases, and air can undergo low-temperature oxidation with crude oil, resulting in an overall oil displacement efficiency of 65.81%. Novel/Additive Information: At present, there is few research on the pore fluid flow and status of oil displacement in tight conglomerate reservoirs with different injection media. This study provides a good understanding of the submicron to nanoscale pore throat structure characteristics of tight oil reservoirs, revealing the state of pore fluids in gravel after displacement by different injection media, and providing support for on-site application of CO 2 enhanced oil recovery in tight conglomerate oil reservoirs.