During polymer flooding in unconsolidated sandstone reservoirs, the pore structure of the rock varies over time due to fluid seepage effects. Detached particles decelerate and deposit in large pores, leading to a reduction in reservoir permeability. To clarify the time-variation mechanism of the pore structure during polymer flooding in unconsolidated sandstone, four core samples with permeabilities ranging from 1 000×10-3 μm2 to 2 000×10-3 μm2 and similar pore structures were used for displacement experiments. Methods such as X-ray diffraction testing, high-pressure mercury injection testing, and CT scanning testing were employed to investigate changes in mineral composition, porosity, permeability, and pore structure parameters such as pore throat radius before and after polymer flooding. The results indicate that after high-volume and high-speed polymer flooding, clay minerals deposit near the outlet end, increasing by 0.85% compared to the initial content. The maximum pore throat radius decreases by 2.86%, and the average pore throat radius decreases by 3.99%, resulting in a 21.8% reduction in permeability. In terms of pore throat distribution, large pores decrease while medium pores increase. Some large pores become smaller due to particle deposition and blockage, and the pore shape factor approaches 1, indicating reduced pore throat heterogeneity.
MA Tian-ci, WANG Ye-fei, DING Ming-chen, ZHANG Fu-min, CUI Chuan-zhi, CUI Shi-zhang.
Experiment on Time-variation Pore Structure during Polymer Flooding in Unconsolidated Sandstone[J].
Science Technology and Engineering, 2026, 26(22): 9510-9516 DOI:10.12404/j.issn.1671-1815.2506357
高压压汞测试实验[13]是运用Micromeritics AutoPore IV 9500压汞仪将汞注入切片,记录注入压力Pc和水银注入量VHg,测定不同注入压力注入汞体积,进而计算不同孔喉半径的方法。注入汞的压力越大,测定的孔喉半径尺寸越小;压力稳定时注入汞饱和度越大,对应孔喉尺寸的占比越大。绘制若干压力点下的压力和水银饱和度曲线,即得到压汞法的岩石毛细管压力曲线。根据毛细管压力曲线特征,计算绘制孔喉结构分布曲线和不同孔喉渗透率分布曲线[14]。
ZhouWensheng, LiuYuan, LiuZhenkun, et al. Research progress and prospect on time varying of physical properties of unconsolidated sandstone oil reservoirs[J]. Fault-Block Oil & Gas Field, 2024, 31(5): 871-876, 899.
[3]
LiuC, ZhouW, JiangJ, et al. Remaining oil distribution and development strategy for offshore unconsolidated sandstone reservoir at ultrahigh water-cut stage[J]. Geofluids, 2022, 2022(1):6856298.
LiCungui, XuShouyu. Law of pore structure variety in reservoir duringa long episode waterflooded development[J]. Petroleum Exploration and Development, 2003, 30(2): 94-96.
JiangRuizhong, QiaoXin, TengWenchao, et al. Impact of physical properties time variation on waterflooding reservoir development[J]. Fault-Block Oil & Gas Field, 2016, 23(6): 768-771.
ZhongYulong, FangYue, LiHongsheng, et al. Variation of reservoir parameters after polymer flooding in Shuanghe Oilfield[J]. Fault-Block Oil & Gas Field, 2020, 27(3): 339-343.
HanPeihui, CaoRuibo, LiuHaibo, et al. Oil reservoir characteri-stics and adaptive compound flooding method after the polymer flooding[J]. Petroleum Geology & Oilfield Development in Daqing, 2019, 38(5): 254-264.
[12]
XiongY, XuH, WangY, et al. The variation mechanism of petrophysical properties and the effect of compaction on the relative permeability of an unconsolidated sandstone reservoir[J]. Marine and Petroleum Geology, 2018, 92: 754-763.
SongLijia. Study on the time-varying law of reservoir physical properties in ultra-high water cut oil fields and the method of water-chemical drive adjustment and tapping potential[D]. Daqing: Northeast Petroleum University, 2023.
XueYong'an, GuoTao, LiuZongbin, et al. Accumulation conditions and key technologies for exploration and development of Suizhong 36-1 Oilfield[J]. Acta Petrolei Sinica, 2021, 42(11): 1531-1542.
LiJinyi, ChenDanqing, ZhouFengjun, et al. Study on difference between relative permeability curves of fresh and washed unconsoli-dated sandstone cores from sealed coring wells[J]. Journal of Xi'an Shiyou University (Natural Science Edition), 2018, 33(1): 39-46.
[19]
LinL L, XuC J, LüH, et al. Property changes of low-permeabi-lity oil reservoirs under long-term water flooding[J]. Processes, 2024, 12(11): 2317.
LiaoKangcen, ChenXuan, LiJianfeng, et al. Analysis onmicrocosmic pore structure characteristics of beach facies reservoir of Feixianguan Formation in Puguang gas field[J]. Contemporary Chemical Industry, 2020, 49(9): 2005-2010.
YangXipu, SunWei. Pore structural features of low permeability reservoirs in Ordos Basin and factor analysis[J]. Special Oil and Gas Reservoirs, 2011, 18(6): 44-47, 125.
CuiZhezhi, SunWei. Study on pore structure of tight sandstone based on high pressure mercury and nuclear magnetic reso-nance: take Shanxi Formation and Shihezi Formation in Sulige Gas Field as examples[J]. Unconventional Oil & Gas, 2020, 7(2): 49-55.
[26]
YangY F, LiY W, YaoJ, et al. Formation damage evaluation of a sandstone reservoir via pore-scale X-ray computed tomography analysis[J]. Journal of Petroleum Science and Engineering, 2019, 183: 106356.
[27]
WangC, ZhangX H, YangT, et al. Stress sensitivity mechanism of pores in unconsolidated sandstone reservoir using NMR technology[J]. Geoenergy Science and Engineering, 2024, 240: 212999.
BaoYanjun, ZhangPenghui, LiangJie, et al. Mineralogy and pore structures of the Ordovician Utica shale in Quebec, Canada[J]. Marine Geology Frontiers, 2020, 36(10): 57-67.
[30]
LiR R, HouX W, ChenL W, et al. Multifractal investigation on multi-scale pore structure heterogeneity of high rank coal reservoirs[J]. Natural Resources Research, 2022, 31(3): 1665-1685.
WangYujun, ZhaoXiaodong, ZhouBoyu, et al. Evaluation of pore structure in low permeability sandstone reservoir based on high pressure-constant velocity mercury injection[J]. Fault-Block Oil and Gas Field, 2022(6): 824-830.
FengJin, ShiLei, GuanYao, et al. Prediction of sandstone reservoir permeability based on image processing and Kozeny-Carman equation[J]. China Offshore Oil and Gas, 2022, 34(2): 67-75.
LiuZongbin, LiChao, LuYan, et al. Fluid occurrence state and permeability evaluation of low-permeability sandstone based on pore structure characterization[J]. Journal of Jilin University (Earth Science Edition), 2024, 54(4): 1124-1136.
YangLiu, GongFei, JiangXiaoyu, et al. Mechanisms behind CO2-brine-sandy conglomerate interactions and resulting variations in mineral components, fluid occurrence, and pores: a case study of the Mahu Sag, Junggar Basin[J]. Oil & Gas Geology, 2025, 46(3): 967-982.
CaoNai, LiHong, HuangLiming, et al. Cross-scale analysis of carbonate rock cores based on pore network model[J]. Science Technology and Engineering, 2022, 22(14): 5582-5587.
WangTao, JiangYuqiang, YangChangcheng, et al. Pore structure and fluid movability of the tight sandstone reservoir in the Tianfu Gas Area of the Sichuan Basin[J]. Science Technology and Engineering, 2025, 25(12): 4900-4912.