New methods and equipment for reliable permeability and saturation measurements in tight rock samples

Background

In the field of petroleum engineering and geosciences, understanding the fluid-flow characteristics in reservoir rocks is crucial for optimizing hydrocarbon recovery. This involves accurately assessing permeability and saturation-dependent relative permeability, which are key parameters in evaluating how fluids move through porous rock formations. Tight rock formations, such as organic-rich mudrocks, present a challenge due to their low permeability and complex pore structures. Traditional methods for measuring these properties are often time-consuming, labor-intensive, and may not provide the precision needed for effective reservoir management. As the industry aims to maximize extraction efficiency and minimize environmental impact, there is a growing need for more reliable and faster assessment techniques.

Current approaches to measuring permeability and saturation-dependent relative permeability in tight rock samples face several significant challenges. Conventional methods like vacuum saturation and spontaneous imbibition are notably slow, often taking days or even weeks to achieve sufficient saturation levels. Additionally, these methods can be inconsistent, leading to unreliable data that complicates reservoir modeling and decision-making. The equipment required for traditional techniques can be specialized and expensive, making it less accessible for routine analysis.

Furthermore, some methods, such as the centrifuge technique, can alter the physical properties of the samples, thereby affecting the accuracy of the measurements. These limitations highlight the need for innovative solutions that can provide quicker, more reliable, and cost-effective assessments of permeability in tight rock formations.

Technology overview

The new methods for assessing permeability and saturation-dependent relative permeability in tight rock samples utilize a pressure-decay setup to provide reliable measurements. The setup includes a reference gas cell, sample holder, pressure valves, a pressure transducer, and a vacuum pump.

The process begins by vacuuming the sample chamber for an hour, followed by filling the reference cell with helium at 200 psi. Opening the upstream valve allows helium to enter the sample chamber, and the pressure decay is recorded. The pressure diffusion equation for a cylindrical core sample is solved numerically using the finite difference method, and permeability is estimated by minimizing the difference between the numerical and measured pressure values. This method is applicable to various sample shapes, including intact, hollowed cylindrical, irregular-shaped, or broken core samples.

The technology differentiates itself by significantly reducing the time required for permeability and saturation measurements compared to conventional methods. Saturating core samples using this new method is approximately 50 times faster than traditional techniques like vacuum saturation and spontaneous imbibition. This speed enhancement leads to quicker relative permeability measurements. Additionally, the workflow allows for fluid-flow measurements in tight rock samples without needing specialized and expensive equipment. It minimizes the impact of the saturation process on the sample's properties compared to the centrifuge method and provides control over the water saturation level, enhancing the accuracy and reliability of saturation-dependent relative permeability measurements.

Benefits

Significantly shorter times for relative and absolute permeability measurements compared to conventional techniques
Fluid-flow measurements in tight rock samples without the need for specialized and expensive equipment
Minimal impact of the saturation process on the properties of the sample compared to the centrifuge method
Control of the water saturation level for making saturation-dependent relative permeability measurements