Miscible Displacement Processes

MISCIBLE DISPLACEMENT

PROCESSES

TM-6012

ENHANCED OIL RECOVERY

OUTLINE

Introduction

General Description

Principle of Phase Behavior

First-Contact Miscible Process

Multiple Contact Miscible Process

Fluid Properties

Factors Affecting Displacement Efficiency Of Miscible Process

INTRODUCTION

Definition

Processes where the effectiveness of

the displacement results primarily from

miscibility between the oil in place and

the injected fluid

Displacement processes:

First-Contact Miscible (FCM)

Multiple-Contact Miscible (MCM)

PRINCIPLES OF PHASE BEHAVIOR

Pressure/ Temperature Diagrams


Pressure/ Composition Diagram Illustrating

Isothermal Compression


Pressure/ Composition Diagram Illustrating Isothermal Compression

FIRST CONTACT MISCIBLE

PROCESS

FCM process normally consists of injecting a relatively small primary slug that is miscible

with the crude oil, followed by injection of a

larger, less expensive secondary slug

Ideally, the secondary slug should be miscible with the primary slug. In contrary,

then a residual saturation of the primary slug

material will be trapped in the displacement

process

FIRST CONTACT MISCIBLE PROCESS

FIRST CONTACT MISCIBLE PROCESS

A basic concern in the design of a process is the phase behavior between the primary slug and the

crude oil and between the primary slug and the

secondary slug fluid that displaces the primary slug

When the reservoir temperature is above the critical temperature of the primary-slug solvent, the

pressure required for complete miscibility between

the slug solvent and the reservoir oil becomes more

difficult to estimate

Under these conditions, the solvent cannot be liquefied and pressure must be above the

cricondenbar

MULTIPLE CONTACT MISCIBLE

PROCESS

The condition of miscibility is generated in the reservoir through in-situ composition

changes resulting from multiple contacts and

mass transfer between reservoir oil and

injected fluid

MCM processes are classified as vaporizing-gas (lean-gas) displacement, condensing and

condensing/vaporizing-gas (enriched-gas)

displacements, and CO2 displacements.

MULTIPLE CONTACT MISCIBLE PROCESS

Vaporizing-gas process

The injected fluid is generally a relatively lean gas ( it contains mostly methane and

other low molecular-weight hydrocarbons)

The composition of the injected gas is modified as it moves through the reservoir

so that it becomes miscible with the original

reservoir oil.


Development of

miscibility

Miscibility does not

develop


Condensing and Condensing/Vaporizing-Gas

(Enriched-Gas) Displacement Process

The injected fluid contains significant amounts of intermediate components (C2

through C6) rather than being a dry gas.

The process depends on the condensation of these components into the reservoir oil,

thereby modifying the oil composition

The modified oil then becomes miscible with the injected fluid

FLUID PROPERTIES

The performance of a miscible displacement process depends on fluid physical properties that affect flow behavior in a reservoir

The properties influence the performance are:

Fluid Density

Fluid Viscosity

FLUID PROPERTIES

Fluid Density

Knowledge of the relative densities of the fluids and fluid mixture is important for the process design

The result in displacement process can be gravity override, underride, or fingering

Fluid Viscosity

Mobility ratio in a displacement process is a direct function of the viscosities and relative permeabilities of displaced and displacing fluids

FACTORS AFFECTING DISPLACEMENT

EFFICIENCY OF MISCIBLE PROCESS

Displacement Efficiency in a miscible process is less than 100%

The magnitudes of the efficiencies depend on a number of factors, including whether a displacement

is conducted as a secondary or tertiary process

In Secondary recovery, it is assumed that there is no mobile water unless water is injected as a part of the

process

In Tertiary recovery, both oil and water will be displaced and will be mobile



Microscopic Displacement Efficiency (No Mobile Water)

The Interfacial Tension (IFT) between displacing (solvent) and displaced (oil) phases. If IFT is zero, then residual saturation in portions of the rock contacted by the displacing phase would be essentially zero

Dispersion and mixing at the microscopic level, combined with the associated phase behavior, are the major reasons that microscopic displacement efficiencies in MCM process in the absence of water are not 100%

Efficiency typically ranges from 90% to 97%



Macroscopic Displacement Efficiency

(No Mobile Water)

Four major factors affect recovery efficiency at

the macroscopic level in a miscible process

Mobility ratio

Viscous fingering

Gravity segregation

Reservoir heterogeneity



Effect of Mobility Ratio

The viscosity of miscible solvents are typically small (



Effect of Viscous Fingering

An adverse viscosity ratio in a miscible process results in viscous fingering, which

leads to reduced volumetric sweep

Effective viscosity ratio, E, that characterizes the effect of viscous fingering:



In the FCM process, the oil recovery was delayed because of the adverse mobility ratio

(early breakthrough of injecting fluid)The

ultimate recovery approached 100%

In the MCM process, the recovery leveled off, the final recovery would not approach 100%.

The viscous fingering not only delay the oil

recovery but also reduce total recovery.



Effect of Gravity

A dimensionless group used to characterize

gravity effects is the viscous/gravity ratio, Rv/g



Vertical sweep efficiency

at breakthrough as a

function of the ratios of

viscous/gravity forces,

linear system



Displacement Efficiency When Mobile Water is Present

The presence of a water phase, flowing or stagnant, has no significant effect on phase behavior in either an FCM process or an MCM process

Miscibility is developed in basically the same manner whether water is present or not

The presence of flowing water has relatively small negative effect on displacement efficiency, but it blocks part of the oil away from the solvent, so it reduce the ability of the solvent to contact and mobilize the oil

It both occurs in FCM and MCM processes

Documents

Miscible Displacement Processes