A Study on the Formation Water Retention State and Production Mechanism of Tight High-Water Saturation Reservoirs Based on Micro-Nanofluidic Experiments

Zhanyang Zhang, Tiantian Dong, Jianbiao Wu, Hui Guo, Jianxin Lu, Junjie Zhong, Liang Zhou and Hai Sun ()
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Zhanyang Zhang: Petroleum Engineering Technology Research Institute, SINOPEC North China Oil & Gas Company, Zhengzhou 450000, China
Tiantian Dong: National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Jianbiao Wu: Petroleum Engineering Technology Research Institute, SINOPEC North China Oil & Gas Company, Zhengzhou 450000, China
Hui Guo: Petroleum Engineering Technology Research Institute, SINOPEC North China Oil & Gas Company, Zhengzhou 450000, China
Jianxin Lu: Petroleum Engineering Technology Research Institute, SINOPEC North China Oil & Gas Company, Zhengzhou 450000, China
Junjie Zhong: National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Liang Zhou: National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Hai Sun: National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China

Energies, 2025, vol. 18, issue 17, 1-15

Abstract: Tight sandstone gas is currently one of the largest unconventional oil and gas resources being developed. In actual reservoir development, the complex pore structure affects the distribution of residual gas and water during the displacement process. However, there is still a lack of experimental research on the multi-scale visualization of pore structures in high-water-content tight gas reservoirs. Therefore, based on the porosity and permeability properties of reservoir cores and the micropore throat structural characteristics, this study designs and prepares three micro-physical models with different permeability ranges. Through micro-experiments and visualization techniques, the microscopic flow phenomena and gas–water distribution in the pore medium are observed. When the water–gas ratio exceeds 5, the produced water type is free water; when the water–gas ratio is between 2 and 5, the produced water type is weak capillary water; and when the water–gas ratio is less than 2, the produced water type is strong capillary water. The latter two types are collectively referred to as capillary water. In the Jin 30 well area, the main types of produced water are first free water, followed by capillary water, accounting for 58.5%. The experimental results of the micro-physical models with different permeability levels show that the production pattern of formation water varies due to differences in pore connectivity. In the low-permeability model, the high proportion of nano-pores and small pore throats requires a large pressure difference to mobilize capillary water, resulting in a higher proportion of residual water. Although the pores in the medium-permeability model are larger, the poor connectivity of nano-pores leads to local water phase retention. In the high-permeability model, micro-fractures and micropores are highly developed with good connectivity, allowing for rapid mobilization of multi-scale water phases under low pressure. The connectivity of nano-pores directly impacts the mobilization of formation water in micron-scale fractures, and poor pore connectivity significantly increases the difficulty of capillary water mobilization, thus changing the production mechanism of formation water at different scales.

Keywords: formation water; tight gas reservoir; micro-nanofluidic experiments; water production types (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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