@article{Chen2025, 
author = {Hao Chen and Pei-Fu Xu and Yong-Xian Zhu and Jia-Yi Yu and Mei Zhang and Xian-Min Zhou and Ming-Cheng Ni and Yi Wu and Xi-Liang Liu},
title = {An experimental study of huff-and-puff oil recovery for tight-tuff heavy oil reservoirs by synergistic with viscosity reducer and CO2 utilizing online NMR technology},
year = {2025},
journal = {Petroleum Science},
volume = {22},
number = {11},
pages = {4736-4752},
keywords = {Tight-tuff heavy oil reservoir, Reservoir rock and live oil, Low limit of pore utilization, CO2 and HDC huff-and-puff, Online NMR, Improved oil recovery},
url = {https://www.sciopen.com/article/10.1016/j.petsci.2025.07.021},
doi = {10.1016/j.petsci.2025.07.021},
abstract = {The tight-tuff heavy oil reservoir exhibits severe heterogeneity and is characterized by high density, high viscosity, and a high wax content, posing significant challenges for its development. While CO2 huff-and-puff (H-n-P) enhances oil recovery, these reservoirs struggle with low displacement efficiency. This study proposes a method that combines CO2 with an oil-soluble viscosity reducer to improve displacement efficiency in the H-n-P process for tight-tuff heavy oil reservoirs. It also focuses on evaluating pore utilization limits and optimizing the injection strategy. Core samples and crude oil from the TH oilfield (a tight-tuff heavy oil reservoir) were used to conduct online NMR core flooding experiments, including depletion development, water, CO2, and HDC (CO2 combined with an oil-soluble viscosity reducer) H-n-P injection processes. A single-porosity model accurately reflecting its geological characteristics was developed using the GEM component simulator within the CMG numerical simulation software to investigate the optimized schemes and the enhanced oil recovery potential for a tight-tuff heavy oil reservoir in the TH oilfield. This model was utilized to evaluate the impact of various injection strategies on oilfield recovery efficiency. The study was designed and implemented with five distinct injection schemes.Results showed that oil was produced primarily from large and medium pores during the depletion stage, while water H-n-P, with CO2 H-n-P, first targeted macropores, then mesopores, and micropores. The lower pore utilization limit was 0.0267 μm. In the HDC H-n-P process, most oil was recovered from water-flooded pores. Still, HDC's lower injection capacity increased the pore utilization limit to 0.03 μm, making micropore recovery difficult. Experimental and modeling results suggest that the optimal development plan for the TH oilfield is one cycle of HDC H-n-P followed by two cycles of CO2 H-n-P. This strategy leverages HDC's ability to promote water and oil recovery in the early stage and mass transfer and extraction capacity of CO2 in later cycles.Additionally, the characteristics of CO2 and HDC H-n-P processes, pore utilization, and recoverable oil (at the pore scale) were evaluated. The results of this study are crucial for refining the reservoir development plan.}
}