Methyl Hydroxyethyl Cellulose as a Promising Additive for Enhanced Oil Recovery

Introduction

The demand for oil and gas has grown significantly because of population growth and economic development worldwide. However, the production of conventional oil fields has started to decline, making the extraction of unconventional reservoirs a viable option. Enhanced Oil Recovery (EOR) is a method for increasing the hydrocarbon recovery of reservoirs and has been widely implemented to improve production. Polymers are key additives used in EOR processes as they can aid in increasing the fluid viscosity, mobility control, and reducing interfacial tension. In this paper, we explore the potential of Methyl Hydroxyethyl Cellulose (MHEC) as an effective polymer in EOR to enhance recoverable oil from unconventional reservoirs.

Overview of Enhanced Oil Recovery

Conventional production methods typically only recover up to 30% of the oil in a reservoir due to the natural reservoir pressure depletion. EOR is a process for improving production by injecting an additional fluid into the reservoir to increase the hydrocarbon recovery. EOR techniques are primarily classified based on the injected fluid type; gas, chemical, or thermal.

Gas injection is the most common method. It involves injecting gas into the reservoir to enhance oil recovery. The injected gas helps mobilize the oil towards the production wells and pushes the oil out of the reservoir. Chemical methods involve the injection of polymers, surfactants, alkaline solutions, and other chemical additives to the reservoir. The polymers help increase the viscosity of the injected fluid, which helps reduce the mobility of the residual oil and improves its sweep efficiency. Alkaline solutions are used to increase the pH of the reservoir to help emulsify the oil. Surfactants reduce interfacial tension between the oil and water by forming emulsions. Thermal methods are used for oil reservoirs containing heavy oil and involve injecting steam into the reservoir to reduce the oil viscosity and improve its mobility.

Polymer Enhanced Oil Recovery (PEOR) is the most effective chemical EOR technique for oil fields that contain high-temperature and high salinity reservoirs. The use of polymers can significantly reduce interfacial tension, improve the sweep efficiency of the injected fluid, and increase the viscosity of the injection fluid, which reduces mobility of the remaining oil and aids in the displacement of the residual oil.

Polymers Used in Polymer Enhanced Oil Recovery

The most commonly used polymer in PEOR is Polyacrylamide (PAM) due to its high solubility and biodegradability. PAM improves the viscosity of the injected fluid, and its molecular weight determines its viscosity, which can be adjusted to suit specific applications. However, PAM cannot withstand high temperatures and salinity, which limits its effectiveness in certain types of reservoirs.

Hydrophobically modified polyacrylamide (HMPAM) is an alternative to PAM that has better salt tolerance. It is a nonionic polymer with hydrophobic side chains grafted onto the polyacrylamide backbone. The nonionic nature of HMPAM allows it to be less sensitive to ionic strength variations. It is effective in low to medium temperature and low saline reservoirs.

Sulfonated polyacrylamide (SPAM) is created by sulfonating PAM, which results in a more anionic molecule. It is effective in high salinity reservoirs and can provide better viscosity at high temperatures. It is less sensitive to temperature and salinity changes, which makes it more effective in harsher reservoirs. However, SPAM is not biodegradable and can cause environmental concerns.

Polymer selection is dependent on the specific reservoir conditions, such as temperature, salinity, pH, and lithology. The polymer must remain stable in the reservoir and maintain its viscosity while under harsh conditions.

Methyl Hydroxyethyl Cellulose in Polymer Enhanced Oil Recovery

Methyl Hydroxyethyl Cellulose (MHEC) is a water-soluble cellulose ether that has found distinctive applications in various fields, including food, pharmaceuticals, cosmetics, and building materials. MHEC is widely used in cement-based building material as an additive for controlling cement workability, improving bonding and film-forming properties, and increasing the strength of concrete.

MHEC is a promising polymer for EOR as it is compatible with a wide range of brines and hydrocarbons, maintaining its viscosity and rheological properties in harsh environments. MHEC can reduce interfacial tension and lower the mobility ratio to improve sweep efficiency. It provides a selective plugging effect on the high-permeability channels in the reservoir and can increase oil mobilization.

MHEC has several advantages over other common PEOR polymers. It is biodegradable, reduces groundwater contamination, and is non-toxic. It has excellent thermal and salt tolerance, making it effective in various reservoir types. Additionally, MHEC can withstand high shear forces, which makes it useful in harsher environments where fluids are injected under pressure.

Conclusion

Methyl Hydroxyethyl Cellulose is a promising polymer for polymer enhanced oil recovery. It offers unique properties and advantages over commonly used polymers such as Polyacrylamide and Sulfonated Polyacrylamide. MHEC is compatible with a wide range of hydrocarbons and brines and can maintain its viscosity and rheological properties in harsh environments. It selectively plugs high-permeability channels in the reservoir and can increase oil mobilization. Its biodegradable, non-toxic, and non-persistent nature makes it environmentally sustainable. MHEC shows potential as a future EOR polymer and warrants further study and development in this field.