Experimental Investigation of Waterflood Performance Challenges in a Low-Permeability Morrowan Sandstone Reservoir: Implications for Mechanistic Modeling and Enhanced Oil Recovery Optimization

Abstract

An indispensable factor to the development of 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 FWU is investigated. The field is divided into two halves (East and west) of the same reservoir and similar geological characteristics. Though the east was prolific on primary recovery it failed on waterflood whiles the west performed efficiently and hence its undergoing WAG CO2-EOR improved recovery technique. Through core-flood experiments, 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. The reservoir primarily consists of quartz, clay minerals (kaolinite, illite, smectite), feldspar, and carbonates. Single-phase injection of low salinity water (SIIW) further reduced permeability and increased differential pressure compared to high salinity water (SCW). Higher flow rates caused significant increments in differential pressure, likely due to velocity-induced fine migration. pH changes and the presence of Al3+, Fe2+, and Zn ions indicated brine reactions. Two flood recovery strategies showed incremental recovery with SIIW injection with observed adverse effects. Fine migrations, clay swelling, scaling, and precipitation were identified as key causes of formation damage during low salinity water flooding. Element-mineral associations showed clays and mineral particles obstructing pores and pore throats. In summary, the principal mechanisms of waterflood inefficiency include low permeability, mineral composition (especially clay minerals), clay mineral reactivity, and increased pressure drop (ΔP). These factors collectively contribute to formation damage, pore plugging, reduced flow capacity, and ultimately the inefficiency of waterflood operations. These insights contribute to the development of effective waterflood strategies and improved recovery techniques for incremental recovery from the FWU-east field especially considering CO2-WAG EOR.