Flow behavior of N huff and puff process for enhanced oil recovery in tight oil reservoirs.

In the present work, the potential of N huff and puff process to enhance the recovery of tight oil reservoir was evaluated. N huff and puff experiments were performed in micromodels and cores to investigate the flow behaviors of different cycles. The results showed that, in the first cycle, N was dispersed in the oil, forming the foamy oil flow. In the second cycle, the dispersed gas bubbles gradually coalesced into the continuous gas phase. In the third cycle, N was produced in the form of continuous gas phase. The results from the coreflood tests showed that, the primary recovery was only 5.32%, while the recoveries for the three N huff and puff cycles were 15.1%, 8.53% and 3.22%, respectively.The recovery and the pressure gradient in the first cycle were high. With the increase of huff and puff cycles, and the oil recovery and the pressure gradient rapidly decreased. The oil recovery of N huff and puff has been found to increase as the N injection pressure and the soaking time increased. These results showed that, the properly designed and controlled N huff and puff process can lead to enhanced recovery of tight oil reservoirs.