A comprehensive experimental study on the mechanisms of waterflood inefficiency in a Morrowan sandstone reservoir

An indispensable factor in developing improved enhanced oil recovery (EOR) is the in-depth insight into the fractional flow mechanistic effects of waterflood performance, especially for an inefficient waterflood operated field. In this study, the inefficiency of waterflood on the Farnsworth Field Unit (FWU) is investigated. The field is divided into two halves (East and West) of the same reservoir with similar geological characteristics. Though the east was prolific on primary recovery, it failed on waterflood, while the west performed efficiently. Through core-flood experiments, fluid-fluid surface charge tests, and rock-fluid surface chemistry analysis, the causative mechanisms are unraveled. X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) analyses were also conducted to assess mineral composition, pore characteristics and distribution. The core samples exhibited extremely low permeability, resulting in a drastic reduction in flow capacity. Single-phase injection of low salinity water (SIIW) further reduced permeability and increased differential pressure compared to high salinity water (SCW). pH and effluent ionic compositions showed a high reactivity within the rock samples. Fine migrations, clay swelling, scaling, and precipitation were identified as key causes of formation damage during low salinity water flooding. Surface charge and compatibility tests revealed fluid-fluid and rock-fluid reactivity and scale formation influenced by high ionic concentrations, temperature, and pressure. Geochemical analysis indicated aragonite, calcite, and dolomite precipitation under reservoir conditions. Element-mineral identification analysis revealed clays and mineral particles obstructing pores and pore throats. Thus, the principal mechanisms of waterflood inefficiency include low permeability, clay mineral reactivity and fluid incompatibility. These factors collectively contribute to formation damage pore and reduced flow capacity. These insights contribute to the development of effective and improved recovery strategies for incremental recovery from the FWU-east field and addition of new knowledge to existing information on low salinity waterflooding on a Morrowan sandstone.