Frontal Stability

Prepared by:Bryan Y.

Cabatingan

A front is stable if it retains the shape of the interface between displaced and displacing fluids as the front moves through the porous medium.

Why is it important?

The frontal stability can influence the displacement efficiency of a flood (i.e. Water, Miscible CO2, Surfactant, Polymer, etc).

We define displacement efficiency as the fraction of oil that has been recovered from a zone swept by a waterflood or other displacement process.

Microscopic displacement

Areal Sweep

Vertical Sweep

Macroscopic displacement

• Oil viscosity is the fluid property with the most influence on sweep efficiency.

• Viscosity controls mobility ratio (M), which is defined as the mobility of the displacing phase divided by that of the displaced phase.

Since,

Thus,

Conformance It is a measure of the uniformity of the flood

front of the injected drive fluid during an oil recovery flooding operation and the uniformity vertically and areally of the flood front as it is being propagated through an oil reservoir (Petrowiki).

Typical Conformance Problems 1. Viscous fingering occurs when M > 1

Top View Side View

2. Matrix – rock channel

3. Water Coning

4. Fracture channeling

5. Horizontal directional high permeability trend

Frontal Advance Theory

Assumptions: 1. The fluids are both incompressible and

immiscible 2. Piston like displacement. Hence, viscous

fingering is neglected. M<1. 3. Porous medium is homogenous4. Displacement is one-dimensional and stable

Case 1: The velocity of the frontal advance neglecting gravity

Where:

Pattern selection and well spacing

Case 2: The velocity of the frontal advance with gravity

Where:

Linear Stability Analysis Calculating frontal advance velocity

considering the rate of growth of a perturbation (viscous fingering) at the front.

Neglecting gravity:

With gravity (dipping reservoir):

The finger grows exponentially if M > 1, decays exponentially if M < 1, and does not propagate if M = 1.

Viscous fingering exponential growth: