ABSTRACT
Offshore heavy oil injection gas extraction is a highly scrutinized area in today's petroleum industry. However, the interaction mechanisms between oil and gas are not clear. To elucidate these mechanisms, an indoor experimental setup was established for research purposes. The effects of different types of gases on heavy oil expansion, mass transfer mechanisms between gas and heavy oil, the influence of gas injection on heavy oil phase behavior, and the testing of minimum miscibility pressures are investigated in this study. The results indicate that CO2 yields the best reduction in the heavy oil viscosity. Both forward and backward multiple contact mass transfer processes demonstrate nonmiscible multiple contact dynamic displacement mechanisms involving CO2 dissolution and condensation, as well as C1 extraction and coextraction. Nonmiscible multiple contact dynamic displacement of natural gas primarily involves limited dissolution and condensation of light hydrocarbon components and intermediate hydrocarbon components, with an extremely weak extraction effect. The minimum miscibility pressures are in the order of CO2 < natural gas < N2. This research provides important experimental evidence and theoretical guidance for further improving offshore heavy oil injection gas technology and practice.
ABSTRACT
Many reports have presented that in tight formation, the flow mechanism differs from a conventional reservoir, such as molecular diffusion, Pre-Darcy flow behavior, and stress sensitivity. However, for CO2 Huff-n-Puff development, it is a challenge to synthetically research these mechanisms. Considering the above flow mechanisms and offshore engineering background, the development plan optimization becomes a key issue. In this paper, a self-developed simulator that satisfies research needs is introduced. Then, based on experimental results, the simulation is launched to analyze the effects of CO2 diffusion, Huff-n-Puff period, and permeability heterogeneity. The results indicate that molecular diffusion makes a positive contribution to the oil recovery factor. Additionally, for offshore reservoirs, limited to the development cost and CO2 facilities corrosion, when the total Huff-n-Puff time is constant, the ratio of 0.5-1.0 between the Huff period and the Puff period in every cycle performs better. Finally, the greater heterogeneity in permeability is much more favorable for the CO2 Huff-n-Puff because of more intensive transport processes in formation. These different scenarios can increase the understanding of the CO2 Huff-n-Puff in tight oil offshore reservoirs.
