Decadal Georeservoir Property Evolution Under Waterflooding: A Hierarchical Statistical and Laboratory-Based Comparative Analysis

The variability in georeservoir properties induced by waterflooding introduces complex predictability challenges, influenced by natural and engineered phenomena. Despite the global prevalence of mature sandstone reservoirs subjected to long-term waterflooding, the effects of waterflooding, especially after extended periods of application, are not well understood. To address this, a comprehensive series of laboratory-based experiments and hierarchical statistical analyses were conducted on a large set of core samples. Some of them experienced over a decade of waterflooding before they were drilled out. This unique real-world dataset ensures high reliability and statistical significance. The laboratory experiments revealed the georeservoir was impacted significantly due to preferential channels development, pore structure modification, and mineralogical changes associated with waterflooding. Specifically, waterflooding was able to influence reservoir wettability, transitioning rock surfaces towards greater hydrophilic, leading to the relative permeability changing. Cast thin sections illustrated that prolonged water flooding significantly dissolved the edges of clastic particles susceptible to water erosion, further elucidating changes in porosity and permeability. Permeability sensitivity tests on current phase samples indicated a general sensitivity ranging from weak to medium-weak. The pore network structure was further analyzed using mercury intrusion porosimetry (MIP), confirming the influence of preferential channels by enhancing the overall porosity-permeability characteristics. Considering the fact that the overall recovery did not increase although the improvement of porosity-permeability, the primary reason behind this phenomenon can be confirmed as the emergence of preferential channels. Moreover, hierarchical statistical models fitted by MIP data quantitatively evaluate the evolution of the georeservoir from the initial to current phase. The validity of the models are also confirmed through statistical approaches. This comprehensive set of laboratory-based and statistical studies provides valuable insights into the impact of waterflooding on sandstone reservoir properties and illuminates the developmental strategy of these reservoirs post-waterflooding.