Multi-Scale Rock Characterization and Modeling for Surfactant EOR in the Bakken

Abstract

Low primary recovery factors in ultratight unconventional reservoirs such as the Bakken, usually in the range of 5-15%, present a potential opportunity for developing effective and economic Enhanced Oil Recovery (EOR) methods. Identified as one of the leading EOR methods for the Bakken, surfactant injection has shown good potential in the laboratory due to its capability to alter wettability, lower interfacial tension (IFT), and reduce residual oil saturation. However, successful implementation of surfactant EOR requires in-depth characterization of the rock-fluid system at multiple scales, ranging from pore scale, to core scale, to field scale. This paper presents a comprehensive study that systematically characterizes Bakken rock properties at the pore scale and the core scale, with the goal of understanding the impact of the pore structure and static and dynamic rock properties on the EOR potential for surfactant injection.At the pore scale, high-resolution 3D X-ray microtomography (microCT) imaging was acquired to evaluate microstructure, interconnected porosity, and fluid distribution. Fluid saturation mapping, before and after surfactant Spontaneous Imbibition (SI), provides fundamental insights into pore-scale recovery efficiency.At the core scale, techniques for measuring static rock properties, including porosity, permeability, and saturation in the Middle Bakken, are reviewed, with a particular focus on measuring matrix permeability across a broad range of values. Fluid properties critical to surfactant injection, such as water salinity and oil polarity, are also discussed. Results from SI experiments are presented with the goal of evaluating imbibition rate and oil recovery with proper scaling. To address the challenges of measuring dynamic rock properties such as imbibition capillary pressure and relative permeability, a plug-scale simulation model was used to history match the laboratory experiment and derive dynamic rock properties that govern the recovery process. The calibrated model was used to address plug-scale recovery efficiency and evaluate recovery uncertainty range, providing fundamental flow characteristics that can be incorporated into upscaled field-scale studies.

A Comprehensive Review on Screening, Application, and Perspectives of Surfactant-Based Chemical-Enhanced Oil Recovery Methods in Unconventional Oil Reservoirs

“…The low recovery factor could be low as 2% OOIP, while the highest was greater than 90% OOIP . The recovery factor is affected by the rock permeability, mineralogy, fluid salinity, temperature, and initial water saturation in addition to the type of chemicals added . Therefore, only cores extracted from similar formation depths can be used to screen different formulations.…”

“…101 The recovery factor is affected by the rock permeability, mineralogy, fluid salinity, temperature, and initial water saturation in addition to the type of chemicals added. 102 Therefore, only cores extracted from similar formation depths can be used to screen different formulations. In recent years, a 3D digital rock based on CT and scanning electron microscope (SEM) data was developed to numerically simulate primary drainage and imbibition pro- cesses.…”

Experimental Study on the EOR Performance of Imbibition and Huff and Puff in Fractured Tight Oil Reservoirs

“…Hydraulic fracturing is the commonly used stimulation method to improve oil recovery in tight oil reservoirs. However, there are still problems such as low production rate, rapid production decline, and poor economic benefits [1][2][3][4]. Hence, new fluids such as imbibition fluids and gases (e.g., CO 2 ) are considered to inject into tight oil reservoirs for further enhanced oil recovery (EOR) by huff and puff [5][6][7][8][9][10].…”

Enhanced Oil Recovery by Cyclic Injection of Wettability Alteration Agent for Tight Reservoirs

“…In general, artificial hydraulic fracturing and then depletion recovery are conducted. However, this method has disadvantages of rapid production decline and low recoverable reserves, and the ultimate recovery factor is usually only 5~15% [1][2][3], which shows great potential for enhanced oil recovery. As for water-wet reservoirs, elastic energy plays a major role in the early stage of development.…”