Abstract
Chemical flooding has been implemented intensively for some years to enhance sweep efficiency in porous media. Low salinity water flooding (LSWF) is one such method that has become increasingly attractive. Historically, analytical solutions were developed for the flow equations for water flooding conditions, particularly for non-communicating strata. We extend these to chemical flooding, more generally, and in particular for LSWF where salinity is modeled as an active tracer and changes relative permeability. Dispersion affects the solutions, and we include this also. Using fractional flow theory, we derive a mathematical solution to the flow equations for a set of layers to predict fluid flow and solute transport. Analytical solutions tell us the location of the lead (formation) waterfront in each layer. We extend a correlation that we previously developed to predict the effects of numerical and physical dispersion. We used this correction to predict the location of the second waterfront in each layer which is induced by the chemical’s effect on mobility. We show that in multiple non-communicating layers, mass conservation can be used to deduce the interlayer relationships of the various fronts that form. This is based on similar analysis developed for water flooding although the calculations are more complex because of the development of multiple fronts. The result is a predictive tool that we compare to numerical simulations and the precision is very good. Layers with contrasting petrophysical properties and wettability are considered. We also investigate the relationship between the fractional flow, effective salinity range, salinity dispersion and salinity retardation. The recovery factor and vertical sweep efficiency are also very predictable. The work can also be applicable to other chemical EOR processes if they alter the fluid mobility. This includes polymer and surfactant flooding.
Highlights
Multi-phase flow in porous media is studied in many disciplines and has a number of engineering applications including contaminant transport, ground water movement in water aquifers and prediction of the behavior of oil and gas reservoirs
Chemical flooding in porous media has broad application where it can be used to reduce the effect of greenhouse emissions by injecting captured CO2 as carbonated water in reservoirs (Sari et al 2020), improve production from gas hydrate formations (Hassanpouryouzband et al 2018), enable nuclear waste storage and remediation of water aquifers (Zheng and Bennett 2002) and is a significant part of enhanced oil recovery (EOR) (Lake et al 2014)
We have presented evidence of this dispersion-induced retardation previously for Low salinity water flooding (LSWF) simulations where salinity caused a change in wettability. (More details can be found in Al-Ibadi et al 2018, 2019b.) The key to this effect is the range of chemical concentrations over which the wettability changes relative to the mixing zone created by dispersion
Summary
Multi-phase flow in porous media is studied in many disciplines and has a number of engineering applications including contaminant transport, ground water movement in water aquifers and prediction of the behavior of oil and gas reservoirs. For a Buckley–Leverett displacement in which there are two phases flowing behind a single formation water shock front, the velocity can be estimated mathematically (El-khatib 2001) This solution does not represent solute transport in such a system, . We extend the work to include the impact of dispersion (either physical or numerical) which makes the fronts non-shock like (Al-Ibadi et al 2019d) and introduces retardation as a physical phenomenon These processes are relevant to LSWF due to the relatively sharp way in which the change in salinity alters wettability. We consider water flooding in 2D non-communicating layers, where we derive the mathematical terms that describe the location of the shock front of the displacing phase relative to that in the other layers.
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