The influence of pore throat characteristics of the Xingzichuan ultra-low permeability reservoir on water flooding mechanisms
DANG Hailong, JIANG Hanqiao , WANG Xiaofeng, ZHAO Xisen, CUI Pengxing, Hou Binchi
1 College of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China 2 Research Institute, Shaanxi Yanchang Petroleum (Group) Co. Ltd, Xi'an 710075, China 3 Shanxi Research Center for Exploration and Development Engineering Technology of Extra low Permeability Oil and Gas, Xi'an 710075, China
The pore throat structure of the Xingzichuan ultra-low permeability reservoir is complex, the size is small, and the micro-heterogeneity is strong, which leads to poor water injection. In order to solve this problem, water flooding experiments were carried out using nuclear magnetic resonance (NMR), and the variation of T2 relaxation time of core samples with different physical parameters under the same injection volume multiple. The T2 relaxation time corresponding to long and small pores is relatively short. The physical meaning of the T2 relaxation time spectrum in reservoir physics is the proportion of pores with different sizes in the total pores in the core. Combining with the physical spherical pore and capillary bundle model, the T2 relaxation time obtained from the experiment is converted to the half diameter of pores in the test sample, and the pore radius distribution of the core sample and the change of oil saturation after water flooding are obtained. The experimental results show that: the displacement efficiency of No.1, No.2 and No.3 samples at 4.0 PV are 62.1%, 57.4% and 72.8%, respectively. Among them, the displacement efficiency of the No.3 sample is the highest and the remaining oil saturation is the lowest. Therefore, for ultra-low permeability reservoirs, it is not that the higher the porosity and permeability, the higher the displacement efficiency, and there is no positive correlation between the porosity, permeability and oil displacement efficiency of rocks; on the basis of the nuclear magnetic resonance water drive experiment, combined with constant velocity mercury injection. The micro-pore throat characteristic parameters of an ultra-low permeability reservoir are analyzed, and the average pore radius, average pore throat ratio and average throat radius are studied. The experimental results show that the maximum difference of the average pore radius of three test samples is less than 3%, so the average pore radius is not the main micro parameter affecting oil displacement efficiency. The oil displacement efficiency is mainly affected by the average throat radius and average pore throat ratio. For hydrophilic reservoirs, capillary force is the driving force. The smaller the average throat radius is, the larger the proportion of small throats is. The dynamic effect of capillary force is stronger, the imbibition effect is more obvious, and the higher the oil displacement efficiency, the larger the average pore throat ratio is, the stronger the heterogeneity is, the greater the seepage resistance of reservoir is, and the lower the oil displacement efficiency is. Therefore, for ultra-low permeability reservoirs, the key to further improve the effect of water drive development is to understand the distribution of pore throat characteristic parameters, optimize the synergistic effect of imbibition and displacement, adjust water injection parameters and reduce the influence of heterogeneity on the seepage field.
Key words：
constant rate mercury injection; pore throat characteristics; nuclear magnetic resonance; water flooding characteristics; average throat radius
DANG Hailong, JIANG Hanqiao, WANG Xiaofeng, ZHAO Xisen, CUI Pengxing, Hou Binchi. The influence of pore throat characteristics of the Xingzichuan ultra-low permeability reservoir on water flooding mechanisms. Petroleum Science Bulletin, 2020, 04: 541-548.
