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Hot water flooding is a thermal recovery technique in which hot water is injected into a reservoir to increase heavy to medium crude oil production. The heat from hot water reduces the viscosity and density of crude oil allowing it to flow easier to the production well. This process, also known as hot water injection increases oil recovery factor and maintains the well production rate for a longer period.
The rise of global development in the last century has seen a rapid increase in the demand for oil. Heavy oils have attracted the world at large due to its abundant reserves and increased development in the past decades. Various techniques such as cold and thermal production have been applied to recover heavy reservoir oils. Cold production methods include chemical flooding (polymer flooding, surfactant flooding, gas flooding etc.), natural depletion and water flooding. Thermal production includes injecting thermal fluid into reservoir, such as cyclic steam stimulation (CSS), steam flooding (SF), and steam assisted gravity drainage (SAGD) or generating heat in the reservoir.
Oil displacement from its location in the reservoir toward the production well is caused by several interconnected parameters. The major benefits are:
- Maintenance of reservoir pressure done by voidage replacement.
- Improved mobility ratio as heat reduces oil phase viscosity 
- Improved areal sweep efficiency as viscous fingering is decreased with increase of the temperature 
- Higher recovery factor as heat reduces interfacial tension and residual oil saturation 
- Improved formation pressure recovery caused by thermal expansion of rocks and fluids 
- Improved vertical sweep efficiency 
Water is heated to a temperature higher than that of the reservoir but lower than the water boiling point at the prevailing reservoir pressure. Hot water is pumped into an injection well drilled parallel to the oil production well as seen below in figure 1.
In the reservoir, hot water flows to cooler surroundings and it loses its heat until it reaches the original temperature of the reservoir. This heat transfer causes the accumulation of a bank of cooled water that continues to grow ahead of the heated zone, which also grows but at a slower rate.
The amount of heat loss to surrounding formations must be calculated in order to determine the cost of heat required to increase the rate of oil production. In general, hot water flooding is relatively a low-cost thermal oil recovery technique that primarily depends on the cost of heat required.
The video below shows the general process of waterflooding.
Hot water injection vs. steam injection process
Hot water injection is less effective than steam injection since steam has a higher heat content than hot water. Nevertheless, hot water flooding is preferred over steam flooding for thin heavy oil reservoirs. Water has a larger viscosity than that of steam, so it provides a larger displacement drive. Moreover, hot water injection allows the usage of higher injection pressures that enable greater temperatures while remaining in the hot water state. Finally, heat losses to the surrounding sands are lower in the case of hot water injection.
Hot water flooding is considered a very effective enhanced oil recovery (EOR) technique for heavy oil after steam injection. Hot water flooding is seen to not only continue to heat the reservoir, but also utilizes the residual heat of the steam. Moreover, the steam tends to preferentially sweep the upper parts of the reservoir, while the hot water tends to flow to the lower parts, thereby improving the overall sweep, even when the permeability of the upper layer is higher than that of the bottom.
- Torabi, F., Qazvini Firouz, A. R., Crockett, M. C., & Emmons, S. 2012. Feasibility study of hot waterflooding technique to enhance heavy oil recovery: investigation of the effect of well spacing, horizontal well configuration and injection parameters. Paper presented at the SPE Heavy Oil Conference, Calgary, Alberta, Canada, 12-14 June. SPE-157856-MS. DOI: https://doi.org/10.2118/157856-MS
- Zhao, David W., and Ian D. Gates. "On hot water flooding strategies for thin heavy oil reservoirs." Fuel 153 (2015): 559-568.
- Wu, Zhengbin, and Huiqing Liu. "Investigation of hot-water flooding after steam injection to improve oil recovery in thin heavy-oil reservoir." Journal of Petroleum Exploration and Production Technology 9, no. 2 (2019): 1547-1554.
- Martin, W. L. "Results of a tertiary hot waterflood in a thin sand reservoir." Journal of petroleum technology 20, no. 07 (1968): 739-750.
- Nmegbu, Chukwuma Godwin Jacob, and Daniel Dasigha Pepple. "2-Dimensional Modeling of Hot Water Injection Application in Thermal Recovery Processes,(A Frontal Advance Approach)." (2017)
- Diaz-Munoz, J., and S. M. Ali. "Simulation of cyclic hot water stimulation of heavy oil wells." (1975).
- Txoilgas,"Water Flooding Concept." Youtube video,1:13.January 22, 2010.https://www.youtube.com/watch?v=Y4Ipuo1IBdk&t=2s&ab_channel=txoilgas