Chemical EOR Formulation for a Clay-Rich Sandstone Reservoir with Reduced Surfactant Consumption

Area of Science:

• Petroleum Engineering
• Enhanced Oil Recovery
• Colloid and Surface Science

Background:

• Alkali-surfactant-polymer (ASP) flooding is an enhanced oil recovery technique that reduces oil-water interfacial tension (IFT) to ultralow values, enabling oil mobilization.
• Surfactant adsorption and retention in clay-rich reservoirs significantly impact the efficiency and economics of ASP flooding.
• Alkali addition to ASP formulations can mitigate surfactant adsorption, making it a crucial component for optimizing oil recovery in challenging formations.

Purpose of the Study:

• To investigate the impact of alkali and surfactant concentrations on the phase behavior of surfactant-brine-oil systems at 75 °C.
• To identify ASP formulations that minimize surfactant and alkali usage while maximizing oil mobilization in a clay-rich sandstone reservoir.
• To evaluate the performance of optimized ASP formulations in terms of oil recovery and surfactant retention.

Main Methods:

• Screening of various surfactants to identify a mixture capable of achieving ultralow IFT (∼0.001 mN/m) at reduced concentrations.
• Formulation of ten ultralow IFT systems, with two selected for detailed evaluation in core flooding experiments.
• Analysis of phase behavior, optimal salinity, oil recovery, and surfactant retention in different core types, including high-clay content sandstone.

Main Results:

• A surfactant mixture was identified that achieved ultralow IFT at low concentrations.
• High cumulative oil recovery (>94%) was achieved across Berea sandstone, Leopard sandstone, and a reservoir core.
• Surfactant retention was low (0.11-0.22 mg/g rock) in high-clay content cores due to alkali presence; reducing surfactant concentration delayed oil production without affecting recovery or adsorption.

Conclusions:

• Alkali addition effectively minimizes surfactant adsorption in clay-rich reservoirs, crucial for efficient ASP flooding.
• Optimized ASP formulations can achieve high oil recovery with reduced chemical consumption.
• While reducing surfactant concentration did not negatively impact oil recovery or adsorption, it resulted in a delay in oil production, offering insights for process design.