Implications of Low Salinity Water-Surfactant Flooding in Field Applications

Implications of Low Salinity Water-Surfactant Flooding in Field Applications

Dr. Rimi Bordoloi

Dibrugarh, Assam.

Abstract – One major problem faced by petroleum industry all over the world is that even after application of conventional oil recovery methods, a large portion of oil is left trapped in many oil reservoirs. The main force behind this entrapment of unrecoverable oil is the combination of capillary forces and strong adhesive forces between the oil and the rock matrix. A relatively new hybrid enhanced oil recovery (EOR) method gaining prominence at present times which can be designed to overcome these limitations is the Low salinity watersurfactant flooding. The process improves oil displacement by combining the benefits of low salinity water injection and surfactant flooding. Low salinity water injection leads to alteration of rock wettability and surfactant flooding reduces interfacial tension between oil and water thereby improving oil recovery. This combined technique improves the displacement and flow of trapped oil. Laboratory studies have shown remarkable improvement in oil recovery; however, field-scale application involves various challenges- operational, environmental, and economic. This paper explains the proposed mechanisms, advantages, limitations, practical applications, and future prospects of this method.

Keywords – petroleum; unrecoverable; surfactant; wettability; displacement.

1. INTRODUCTION

   Oil production in reservoirs typically undergo three stages of production: primary, secondary, and tertiary recovery. In the primary stage, oil is produced using natural energy of the reservoir. In the secondary stage, water or gas is injected to maintain pressure which helps in improvement in oil recovery. However, even after primary and secondary recovery, a large fraction of oil remains trapped within the reservoir pores due to combined capillary forces and unfavourable interactions between rock and fluids. To address this issue, enhanced oil recovery methods are used. Enhanced Oil Recovery (EOR) techniques help in the extraction of this remaining oil. One such method that is gaining widespread prominence is the Low Salinity Water Flooding. Low Salinity Water Flooding involves modifying the ionic concentration and salt composition of the injected water. This process results in the alteration of the interaction between rock and fluids. Surfactant flooding, one of the common chemical EOR method, on the other hand, involves the injection of chemicals that reduce the interfacial tension between oil and water allowing oil droplets to move more freely. Thus, the process of Low Salinity Waterflooding can be made more beneficial by the introduction of surfactant into it and thus when these two methods are combined, they create a more effective

   system for mobilizing trapped oil. This technique of enhancing oil recovery was put forward by Alagic and Skuage (2011) known as Low Salinity Water Surfactant Flooding resulting from the unification of the two processes.

2. PRINCIPLE OF LOW SALINITY WATERFLOODING AND SURFACTANT FLOODING

   In literature numerous researchers have suggested numerous mechanisms that lead to incremental oil recovery resulting from Low salinity waterflooding. However, the following mechanisms play an important role in improving oil recovery:

   1. Wettability alteration

      Wettability is the ability of a fluid to adhere to or spread on to a solid surface in the presence of other fluid. The distribution and transportation of different fluid phases in the reservoir is carried on due to the property of wettability. Rocks in many reservoirs are oil wet, i.e., they tend to hold oil tightly on their surfaces. Injecting low saline water results in changes in the chemical balance at the rock surface, making it more water-wet. This results in oil being released more easily from the rock.

   2. Ion Exchange Mechanism

      The injection of low salinity water causes ion exchange between the injected fluid and the rock surface. This process helps in releasing oil that was previously attached to the rock.

   3. Double Layer Expansion

      When low salinity water is injected into the reservoir, it leads to increase in the thickness of the electrical double layer around rock particles. The attractive forces between oil and rock starts weakening, thereby making it easier for oil to move.

3. PRINCIPLE OF SURFACTANT FLOODING

   The main mechanism behind surfactant flooding that leads to improved oil recovery are:

   1. Reduction of Interfacial Tension Surfactants are surface active agents that reduce the force separating oil and water. When this force decreases, oil droplets can move more freely through the pores of the rock which makes it easier to extract them.

   2. Microemulsion Formation

      Surfactants can form stable mixtures of oil and water called microemulsions. These help in transporting oil toward production wells.

   3. Mobility Improvement

      By reducing capillary forces, surfactants improve the flow of oil and increase displacement efficiency.

4. COMBINED MECHANISM OF LOW SALINITY WATERSURFACTANT FLOODING

   The hybrid method of combining low salinity water and surfactants create a synergistic effect that enhances oil recovery through:

   1. Improved Sweep Efficiency

      The injected low saline water with the added benefit of surfactant can displace oil more uniformly across the reservoir, reducing bypassed zones.

   2. Enhanced Wettability Change

      The availability of surfactants strengthens the wettability alteration caused by low salinity water.

   3. Improved Oil Mobilization

      The combination of reduced interfacial tension and favourable wettability conditions lead to better movement of oil.

5. BENEFITS IN FIELD APPLICATION

   1. Higher Oil Recovery

      Low Salinity Water Surfactant flooding leads to increase in oil production. It helps to recover oil that would otherwise have remained trapped after primary and secondary oil recovery methods.

   2. Better Utilization of Chemicals

      Use of Low salinity water minimizes the loss of surfactants on rock surfaces. This means that less chemical is wasted thereby leading to improving recovery efficiency.

   3. Cost Reduction

      This technique requires water, which is the main injected fluid and only a small amount of chemical such as surfactant. This makes the overall cost lower compared to other chemical flooding methods.

   4. Improved Sweep Efficiency

      The injected fluid can cover a larger portion of the reservoir and improves both microscopic and macroscopic sweep efficiency, ensuring that more oil is displaced and produced.

   5. Environmental Advantage

      At present times, the need of the hour is to find methods which are low cost and environment friendly and this technique results in reduced chemical usage leading to lower environmental impact compared to heavy chemical flooding techniques.

6. CHALLENGES IN FIELD APPLICATION

   Despite the numerous advantages, several issues arise hen applying this method in real reservoirs:

   1. Complex Reservoir Heterogeneity Reservoirs are not uniform. Due to differences in rock properties like porosity, permeability, flow can be uneven, reducing the

      effectiveness of the flooding process.

   2. Chemical Stability

      High temperature and pressure in reservoirs can degrade and break down surfactants which in turn reduces their performance.

   3. Formation Damage

      Low salinity water can cause swelling of clay minerals or movement of fine particles, which may block pore spaces and reduce permeability.

   4. Scaling and Precipitation

      The reaction between the minerals present in the reservoir and injected fluids may sometimes form deposits that clog the reservoir and reduces the efficiency of the process.

   5. Economic Cost

      Although the method can improve recovery, the high initial cost of chemicals, water treatment, and infrastructure affects the economic feasibility of the process.

7. PRACTICAL CONSIDERATIONS FOR FIELD

   USE

   For successful implementation, several factors must be considered:

   1. Reservoir Screening

      The first step is to check the suitability of the reservoir as all reservoirs are not suitable. Proper evaluation of rock type, fluid properties, and salinity is necessary.

   2. Design of Injection Process

      The concentration of surfactant, the salinity of injected water and the salinity level must be carefully optimized for each reservoir.

   3. Pilot Testing

      Field tests should be first carried out on a small-scale before

      full-scale application to ensure effectiveness of the technique in real field.

   4. Monitoring and Control

      Continuous monitoring of production and pressure helps in adjusting the process for better performance.

   5. Water Management

      Since the process entails the use of large volumes of water, the treatment and disposal systems must be properly designed for the process to be effective.

8. ENVIRONMENTAL AND OPERATIONAL

   IMPLICATIONS

   1. Water Handling

      As large volumes of water are required, managing large quantities of injected and produced water poses a major operational challenge.

   2. Reduced Chemical Impact

      The lower usage of chemicals reduces environmental risks compared to traditional chemical flooding methods.

   3. Risk of Reservoir Damage

      Improper design can lead to reduction in permeability and other reservoir properties, affecting long-term production.

   4. Waste Disposal

      Produced water containing chemicals must be treated before disposal otherwise it may adversely impact the environment.

9. ECONOMIC CONSIDERATIONS

   1. Cost of Chemicals

      Surfactants can be expensive, so their usage must be optimized.

   2. Infrastructure Cost

      Additional facilities for water treatment and injection are required.

   3. Incremental Oil Recovery

      Economic success depends on the additional oil recovered compared to the cost of implementation.

   4. Risk Analysis

      Uncertainty in reservoir performance must be considered before investment.

10. FUTURE SCOPE

    The technique is still evolving, and future improvements may include:

    1. Development of advanced surfactants

       Development of more stable and efficient surfactants which are able to withstand harsh reservoir conditions.

    2. Optimization of different composition of smart water

       Formulation of smart water injection with optimized ion composition to maximize oil recovery.

    3. Hybrid EOR Techniques

       Integration with other EOR methods such as polymer flooding and comparing the results.

    4. Digital Monitoring

Application of digital monitoring and simulation tools to optimize the process.

These advancements can make the process more reliable and economically viable for use.

CONCLUSION

Low salinity watersurfactant flooding is a promising hybrid EOR method for enhancing oil recovery from reservoirs by combining wettability alteration and interfacial tension reduction leading to mobilization of trapped oil. However, its success in field applications depends on careful design, reservoir suitability, and proper management of operational challenges. With continued research and ongoing field testing, this method has strong potential in improving oil production in the future and sustaining the energy when planned properly.

REFERENCES

1. Afeez Gbadamosi, Shirish Patil, Dhafer Al Shehri, Muhammad Shahzad Kamal,

   S.M. Shakil Hussain, Emad W. Al-Shalabi, Anas Mohammed Hassan; Recent advances on the application of low salinity waterflooding and chemical enhanced oil recovery, Energy Reports, Volume 8,2022, Pages 9969-9996 (2022).

2. Araz et al.; Experimental study of combined low salinity and surfactant flooding effect on oil recovery, Oil & Gas Science and Technology Revue dIFP Energies Nouvelles (2021).

3. Iravani, M., Khalilnezhad, Z. & Khalilnezhad, A; A review on application of nanoparticles for EOR purposes: history and current challenges. J Petrol Explor Prod Technol 13, 959994 (2023).

4. Stephenson, Tim & Oswald, Darin & Dwyer, Pat & Brown, Derek & Ndefo, Emeka & Kiran, Sumit & Smith, Jeff & Gaffney, Breandan; Core Floods vs.

   Field

5. Pilot Effectiveness of Microemulsions in Conventional and Unconventional Waterfloods. 10.2118/195854-MS(2019).