The Chemical Engineering Department at the College of Engineering, University of Baghdad, held a M.Sc. thesis examination titled:

“ Study The Influence of Surfactant-Polymer on Enhancement Oil Recovery of a Carbonate Reservoir ”

On Tuesday, December 31, 2024. By the student “Rafal Salah Abdullah” and supervised by Prof Dr. Hussein Q. Hussein and Dr. Rana R. Jalil.

The examination committee consisted of Prof. Dr. Ibtehal Kareem Shakir as Chairman and the membership of Prof. Dr. Hameed Hussein Alwan and Asst. Prof. Dr. Tuqa Abdulrazzaq Flayh. The thesis was accepted after conducting a public discussion and listening to the student’s defense. The thesis was summarized as follows:

The aim of the study:

The primary goal is to modify the wettability of carbonate rocks and reduce interfacial tension to enhance oil recovery, which is achieved using polymers and surfactants. Additionally, it investigates their effect on boosting oil output through a flooding system. More precisely, the goals are:

1. Investigate the effect of PVA and CTAB on the wettability of carbonate rocks to enhance oil recovery
2. study the influence of polymer and surfactant on influence water/oil interfacial tension and surface tension to assess their effectiveness.
3. Evaluate the impact of using smart water in conjunction with PVA and CTAB on interfacial and rock properties and oil recovery.
4. Study the performance of these chemical agents across various flow rates to determine optimal conditions for recovery.

Abstract

Increasing oil recovery from carbonate reservoirs presents significant challenges due to their complex properties, which affect the efficiency of extraction. This study investigates the effectiveness of polyvinyl alcohol (PVA) and cetyltrimethylammonium bromide (CTAB) as stand-alone agents for tertiary recovery, as well as the role of ionically modified smart water in secondary recovery. The study focuses on critical parameters for oil displacement and recovery, such as wettability alteration, interfacial tension (IFT), and surface tension (ST), using different brines and brine compositions. Carbonate rock samples were supplied by Thiqar Oil Company from the Mishrif Formation.

Several concentrations of CTAB surfactants were added to the brine (B1), and the surface tension (solution/air) and interfacial tension (solution/crude oil) were measured. CTAB, tested at 500 ppm in NaCl brine, reduced surface tension from 74 to 42 mN/m and IFT from 28 to 15 mN/m. In smart water with Mg²⁺ and SO₄²⁻ ions in a 1:1 ratio, a more significant effect was observed: surface tension dropped further to 30.15 mN/m, and IFT decreased to 12 mN/m. The presence of these ions also led to a shift in wettability, from water-wet to more favorable conditions, with the contact angle decreasing from 89° to 33° in just 30 minutes.

Similarly, several concentrations of PVA were added to brine, and their effects on surface tension and interfacial tension were analyzed. PVA was also tested and reduced surface tension to 44 mN/m in brine, with even better results when combined with smart water. The lowest surface tension (29 mN/m) and IFT (11.8 mN/m) were observed in smart water with a 1:1 Mg²⁺/SO₄²⁻ ratio, demonstrating PVA’s ability to enhance wettability and increase water adsorption on the carbonate rock surface. The contact angle was approaching zero, indicating a full transition to water-wet condition.

Enhancing the oil displacement process in carbonate reservoirs—which typically face challenges in recovery—requires this complete transition to water-wet conditions. This full shift to water-wet conditions is vital for improving oil displacement in carbonate reservoirs, which are generally resistant to recovery.

The study also evaluated the effect of various ion compositions in smart water (Na+, Cl-, SO₄²-, Mg²+) on oil recovery during secondary recovery. The results showed significant recovery rates of 37.5%, 23.6%, 61%, and 47% for different plugs, highlighting the importance of Mg²⁺ and SO₄²⁻ ions in altering the rock-fluid interaction and improving recovery. CTAB injections (500 ppm in smart water with a 1:1 Mg²⁺/SO₄²⁻ ratio) resulted in incremental oil recoveries of 12.5% and 13.5% in plugs P1 and P2, respectively. PVA injections (2000 ppm) resulted in higher incremental recoveries, 33.3% and 24.5%, in plugs P3 and P4, respectively. These differences in recovery rates were influenced by flow rates and geological heterogeneity, with higher flow rates leading to more efficient recovery.

The findings of this study demonstrate that combining ionically modified smart water with surfactants (CTAB) and polymers (PVA) can significantly improve oil recovery in carbonate reservoirs. By optimizing fluid-rock interactions and surface chemistry, these techniques enhance oil displacement, leading to higher recovery rates. This research provides valuable insights for developing chemical EOR strategies, particularly for carbonate reservoirs where improving oil production depends on modifying wettability and reducing interfacial tension