Evaluation and prediction of Enhanced Oil Recovery (EOR) by Low Salinity Water Flooding (LSWF) injection
Abstract
Low Salinity WaterFlood (LSWF) injection is an Enhanced Oil Recovery (EOR)
method proven to be effective by extensive experimental studies. Correct implementation
of this method in reservoir-scale simulations requires reliable estimation of relative
permeability data. However, due to the ongoing debate regarding the dominant
mechanism in this process and the inadequate understanding of complicated brine-oil-rock interactions, only a few models have been suggested to estimate relative permeability
associated with LSWF for either carbonate or sandstone rocks. Existing models simulate
the impact of LSWF based on geochemical interactions; however, the fluid-fluid
interaction has been overlooked. Some models depend on the cation-exchange capacity
of clay which is not adequate for clay-free rock. In contrast, others are based on weighting
factors such as the divalent ions desorption, which is case dependent.
This study presents a novel semi-empirical model of LSWF relative permeability, after
high salinity water flooding, based on incremental oil recovery measured during low
salinity injection. Therefore, it can be applied to all rock types, fluid systems, and
wettability conditions regardless of the active mechanism. The relative permeability at
the high salinity water flooding, krHS and incremental oil recovery during low salinity
injection were inputs to the model for predicting the low salinity kr curve, krLS and,
consequently, this model can be used to assess the performance of LSWF. Well-known
mechanisms in literature on the incremental oil recovery during LSWF are reviewed
including micro-dispersion. In this work, correlation between the incremental oil recovery
and the amount of micro-dispersion has been employed for sensitivity analysis, and
evaluation of the new model's response among various levels of incremental oil recovery.
This new model has been validated utilising 12 coreflood datasets obtained from core
flooding experiments under both unsteady-state and steady-state flooding conditions or
protocols. A new steady-state experiment has been performed in this study to produce the
first reliable relative permeability data that is needed for validation. This dataset, along
with the unsteady-state dataset obtained under tertiary and secondary mode by other
researchers in our group at Heriot-Watt University, has been used to validate the new
model and to quantify the effect of LSWF injection on the relative permeability. Five
experiments have already been published in literature by other researchers from our
group, while the other four experiments have not yet been published. Additional two more
experimental data from other group researchers available in the literature were deployed
for further verification. Due to its mechanism independence, the new model suggested in this thesis can be applied for efficient performance screening of all LSWF injection
scenarios, which is invaluable for the oil and gas industry’s decision-making process.
The results confirm the difference in relative permeability curves between high-salinity and low-salinity injections caused a decrease in water relative permeability and
an increase in the oil relative permeability. They also prove that low-salinity brine can
shift the rock wettability from oil-wet or mixed-wet towards a more water-wet condition.
The obtained relative permeability curves extend across a substantial saturation range,
making this valuable information necessary for numerical simulations. To the best of our
knowledge, the data from the steady-state experiment is a first in assessing the impact of
low-salinity waterflooding at a steady-state condition using a reservoir live crude oil and
long reservoir core sample at reservoir condition. The results of this study are of utmost
importance for the oil and gas industry.