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Alkaline-surfactant-polymer (ASP) flooding: Difference between revisions

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Alkaline-Surfactant-Polymer Flooding (ASP) is one of the proven technology in chemically enhanced oil recovery (CEOR) methods, which can be used for recovering heavy oil containing organic acids from sandstone formations. ASP Flooding belongs to a class of CEOR method that uses a combinations of chemicals i.e. Alkali, Surfactant and Polymer.

CEOR Classification

ASP Flooding Mechanism

The recovery efficiency of a flood is conventionally decomposed into the product of the volumetric sweep efficiency and displacement efficiency[1]. Polymer can increase the viscosity of injection water so as to improve the mobility ratio between the displacement and displaced phases, which is the basic principle of ASP flooding.

It involves injection of alkali to generate in situ surfactants, surfactants to reduce interfacial tension between displacing and displaced phase and polymer to improve mobility ratio and thus sweep efficiency, and is followed by extended waterflood. In a system with water and oil, a surfactant will reduce the interfacial tension between the two liquid phases, which “liberates” residual oil held by capillary forces i.e. a reduction of capillary pressure in the reservoir, leaving it water-wet. This “liberated” oil can now be more easily mobilized and produced.

Concentration of alkali, surfactant and polymers used in the process depends upon oil type, salinity of the solution, pressure, temperature and injection water quality. Polymer is used for improving mobility ratio which greatly contributes to the expansion of sweep efficiency[2]. The use of the alkali and the surfactant is to reduce interfacial tension between the displacing phase and the oil phase so as to improve the oil displacement efficiency. Alkali could also reduce the adsorption of expensive surfactants.

ASP Flood

ASP Flooding Screening Criteria

Enhanced oil recovery (EOR) processes are well known for their efficiency in incrementing oil production; however, the selection of the most suitable method to adopt for specific field applications is challenging. Therefore, it is pertinent to consider certain screening parameters before application of any recovery method and the most important ones are geology and mineralogy. Few important parameters to consider for ASP Flooding are:

  • Preferred for sandstones reservoir
  • Stratification desirable
  • Reservoir Temperature less than 200 °F
  • Salinity < 20,000 ppm
  • Lower Ca++ and Mg++ contents
  • Formation relatively homogeneous
  • Oil Viscosity < 35 cp and API Gravity > 20 °API
  • Oil composition is light to intermediate components
  • Oil Saturation > 35 %
  • Average Permeability > 10 md

ASP Chemical Contents

Chemical composition of ASP Flooding is based on:

  • Alkaline Content

Type of Alkaline for ASP is Sodium Hydroxide (NaOH) and Sodium Carbonate (Na2CO3). Alkali is often added to the aqueous solution to increase efficiency as it helps to reduce surfactant adsorption to the rock[3].

Potential Alkali reactions in formation are:

2NaOH + Ca+2-> 2Na+ + Ca OH)2

2NaOH + Mg+2-> 2Na++ Mg(OH)2

Na2CO3 + Ca+2-> 2Na+ + Ca CO3

Na2CO3 + Mg+2-> 2Na+ + Mg CO3

  • Surfactant

Type of surfactant in ASP are:

  1. Alkyl Benzene Sulfonates

  2. Petroleum Sulfonates

  3. Lignosulfonates

  4. Petroleum Carboxylates

  5. Biologically Produced Surfactants

These surfactants aid in the generation of an ultra-low IFT between the oil and water.

  • Polymer

In ASP flooding, types of polymer is Hydrolyzed Polyacrylamide (HPAM). A water-soluble polymer is usually added to increase the viscosity of the water phase to improve mobility control[4]. The effectiveness of HPAM relies in the following chemical features:

The lack of oxygen single bonds (-O-) in the polymer backbone (carbon chain) provides thermal stability.

The presence of non‐ionic hydrophilic group (i.e. -CONH2) promotes chemical stability.

The carboxyl group (-COO-) resulting from the hydrolysis of the amide groups reduces the adsorption tendency of HPAMs onto rock surfaces and increases its viscosity.

The cost of the polymer is relatively low[5].

HPAM Structure

ASP Benefits

ASP flooding has the following benefits over other CEOR methods:

  • ASP is a cost‐effective process.
  • The synergistic effects of the ASP mixture make this process attractive for EOR applications.
  • The amount of chemical consumed per unit volume of oil produced during ASP flooding is usually low when the three chemical slugs (alkaline, surfactant and polymer) are injected in sequence or as a single slug[6].

ASP Flooding Limitations

Some of the limitations of the ASP process are related to:

  • Issues with chemical separation.
  • Water treatment cost.
  • Emulsions instability and scale formation that could make the process complex.
  • Issues with creating contact with the formation oil.
  • Potential corrosion /scale problems in the pipeline and equipment.

References

  1. A. Clarke, A. M. Howe, J. Mitchell, J. Staniland, and L. A. Hawkes, “How viscoelastic-polymer flooding enhances displacement efficiency,” SPE Journal, vol. 21, no. 3, pp. 675–687, 2016.
  2. S. Mishra, A. Bera, A. Mandal, S. Mishra, A. Bera, and A. Mandal, “Effect of polymer adsorption on permeability reduction in enhanced oil recovery,” Journal of Petroleum Engineering, vol. 2014, Article ID 395857, 9 pages, 2014.
  3. M. Y. Khan, A. Samanta, K. Ojha, and A. Mandal, “Design of alkaline/surfactant/polymer (ASP) slug and its use in enhanced oil recovery,” Petroleum Science and Technology, vol. 27, no. 17, pp. 1926–1942, 2009.
  4. www.shell.com/chemicals/enordet
  5. Abidina A. Z., Puspasaria T., Nugroho W. A. (2012). Polymers for enhanced oil recovery technology. Procedia Chemistry, 4, 11–16.
  6. Froning H. R., Leach R. O. (1967). Determination of chemical requirement and applicability of wettability alteration flooding. Journal of Petroleum Technology, 19(6), 839–843.