improved oil recovery by injection of water and...

Improved Oil Recovery by Injection of Water and Gas

Dr. Amin Azhdarpour

Depar tment Of Pet ro leum Eng ineer ing , Marvdasht Branch, Is lamic Azad Un ivers i ty, Marvdasht , I ran .

E-mai l : aminazh22@gmai l .com;amin [email protected]. i r

Course outline 1. Introduction

2. Water flooding

3. Gas injection

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References 1. Enhanced Oil Recovery, Green D. and P. Willhite, SPE Pub., 1998.

2. Water Flooding, Willhite P., SPE Pub., 1986.

3. Enhanced Oil Recovery, Lake L. W., Prentice Hall, 1989.

4. Enhanced Oil Recovery, Lateil, Gulf Pub. Co.,1980.

5. Fundamental of Enhanced Oil Recovery, Poollen H.K., Penn Well, Books, 1981.

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Chapter 1

INTRODUCTION

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Oil recovery mechanisms

1. Primary recovery

2. Secondary recovery

3. Tertiary recovery

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1. Primary recovery Primary oil recovery refers to the process of extracting oil either via thenatural rise of hydrocarbons to the surface of the earth or via pumpjacks and other artificial lift devices.

Primary recovery is also sometimes referred to as pressure depletionbecause it necessarily involves the decline of the reservoir pressure.

In fact, only around 5% - 15% of the well’s potential are recovered fromthe primary method.

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Primary recovery mechanisms

2. Secondary recovery Secondary oil recovery refers to the additional recovery that results from the conventional methods of water injection and immiscible gas injection.

The technique was called pressure maintenance.

The added energy stimulates the movement of oil, providing additional recovery at increased rates of 15 to 60%.

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Water flooding This method involves the injection of water at the base of a reservoir to:Maintain the reservoir pressure,

Displace oil (usually with gas and water) towards production wells.

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Gas injection This method is similar to waterflooding in principal, and is used tomaintain gas cap pressure even if oil displacement is not required.

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3. Enhanced Oil recovery (Tertiary recovery)

Enhanced oil recovery (EOR) is oil recovery by the injection of materials not normally present in the reservoir.

This definition covers all modes of oil recovery processes and most oil recovery agents.

Tertiary recovery is any technique applied after secondary recovery.

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Oil recovery categories

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Improved Oil Recovery (IOR)Engineering methodsthat are used tosupplement the naturalreservoir drive of an oilreservoir and increase itsultimate production.

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Forces involved in multiphase fluid system

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Capillary forces

Viscous forces

Gravity forces

1. Capillary forces Capillary forces in a multiphase system includes:

Surface tension (ST) and interfacial tension (IFT)

Rock wettability

Capillary pressure

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ST & IFTThe term surface tension is used for the specific case in which the surface is between a liquid and air.

Surface tension of water and its vapor at room temperature is about 73 dyne/cm.

If the surface is between two different liquids or between a liquid and a solid the term is interfacial tension.

IFT’s between water and pure hydrocarbons are about 30 to 50 dynes/cm at room temperature.

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Wettability Wettability is the tendency of one fluid to spread on or adhere to a solid surface in the presence of a second fluid.

◦ Water wet (Ѳ<90)

◦ Oil wet (Ѳ>90)

◦ Intermediate wettability (Ѳ is close to 90)

◦ Mixed wettability

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Water wet & Oil wet

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Capillary pressure, PcWhen two immiscible fluids are in contact, a discontinuity in pressureexists between the two fluids, which depends upon the curvature of theinterface separating the fluids. We call this pressure difference thecapillary pressure and it is referred to by Pc.

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2. Viscous forces Viscous forces in a porous medium are reflected in the magnitude of the pressure drop that occurs as a result of flow of a fluid through the medium.

Viscous forces in a porous medium can be expressed in terms of Darcy’s law:

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3. Gravity forcesThe partial or complete separation of fluids in a subsurface reservoir due to difference in density.

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Viscous Gravity Ratio (VGR)Ratio of viscous force to gravity force is called VGR.

Viscous force is controlled by velocity and fluid viscosity.

Gravity force is determined by density difference betweendisplacing and displaced fluids.

Low VGR (gravity force dominated): Gravity override

High VGR (viscous force dominated): Viscous fingering

In general: Higher VGR Higher recovery

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Several VGR equations

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Capillary number (Nc)Capillary number is the ratio of viscose force to capillary force.

Three main definitions are provided by:◦ Moore and Slobod

◦ Melrose and Brandner

◦ Abrams

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Definitions/Equations

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Residual oil VS Nc

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Some facts about NcAt capillary number less than about 10-6, the residual oil is relativelyconstant and independent of magnitude of Nc.

Waterfloods typically operates at conditions where Nc<10-6 and Ncvalues on the order of 10-7 are probably most common.

At values on the order of 10-2, virtually all oil is recovered.

The value of Nc can be increased by:Increasing the flow rate of displacing fluid

Increasing the viscosity of the displacing fluid

Reducing IFT between displacing and displaced fluid

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Mobility ratio (M)

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Cont…

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Mobility ratio and sweep efficiency

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EOR methodsChemical methods are characterized under improved water flooding methods.

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Oil gravity and EOR methods

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Oil viscosity and EOR methods

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Reservoir permeability and EOR methods

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Reservoir depth and EOR methods

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Water flooding Waterflooding consist of injecting water into the reservoir. It is the most post-primary recovery method. water is injected in patterns or along the periphery of the reservoir.

Mechanism:Water Drive

Increased Pressure

Problems: formation damage, high oil viscosities results in higher mobility ratio, extensive heterogeneity is not acceptable.

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Cont…

Technical screening guides:

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Gravity >25 API

Viscosity <30 cp

Composition Not critical

Oil saturation >10% mobile oil

Formation Sand stone and carbonate

Permeability Not critical

Depth Not critical

Temperature Not critical

Hydrocarbon miscible flooding Hydrocarbon miscible flooding consists of injecting light hydrocarbons through the reservoir to form a miscible flood.

Three different methods are used:LPG gas drive which is the injection of 5% PV slug of PLG such as propane,

followed by natural gas and water.

Enriched gas drive which is the injection of 10-20% PV slug of natural gas that is enriched with C2-C6, followed by lean gas and water.

High pressure (vaporizing) gas drive which is consist of injecting lean gas at high pressure to vaporize C2-C6 components from the crude oil being displaced.

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Cont… Mechanism:Generating miscibility to mobilize oil

Increasing the oil volume (oil swelling)

Decreasing the viscosity of oil

Problems:Viscous fingering results in poor se\weep efficiency

Large quantities of expensive products are required

Solvents may be trapped and not recovered.

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Cont…


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Gravity >35 API

Viscosity <10 cp

Composition High percentage of C2-C7

Oil saturation >30% PV



Depth >2000 ft for LPG and >5000 ft for high pressure gas


Nitrogen and flue gas floodingNitrogen and flue gas flooding are oil recovery methods which use these inexpensive non-hydrocarbon gases to displace oil either through miscible or immiscible mechanism.

Mechanism: Vaporizing the lighter components of the crude oil

Providing a gas drive where a significant portion of the reservoir volume is filled with these gases

Problems:

Viscous fingering

Corrosion due to the use of flue gas

Separation of non-hydrocarbon gases from the salable produced gas

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Cont…


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Gravity >24 API (>35 API for nitrogen)

Viscosity <10 cp

Composition High percentage of C2-C7




Depth >4500 ft


Carbon dioxide flooding Carbon dioxide flooding is carried out by injecting large quantities of CO2 into the reservoir. Although CO2 is not truly miscible with the crude oil, it extracts the light to intermediate components from the oil. And if the pressure is high enough, develops miscibility to displace the crude oil.

Mechanism:Generation of miscibility

Swelling the crude oil

Lowering the oil viscosity

Lowering the IFT between the oil and CO2

Problems:

Early breakthrough of CO2, Corrosion, CO2 separation from saleable hydrocarbons, repressurizing CO2 for recycling, high amount of CO2 is required.

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Cont…


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Gravity >26 API (preferably >30)

Viscosity <15 cp (preferably <10 cp)

Composition High percentage of intermediates, C5-C20

Oil saturation More than 30% PV

Formation Sand stone and carbonate with minimum fracture


Depth Deep enough to allow for miscibility generation


Surfactant polymer flooding Surfactant/polymer flooding also called micellar/polymer is consists of injecting a slug that contains water, surfactant, salt, usually a coselvent (alcohol). The surfactant slug is then followed by polymer-thickned water. The size of surfactant slug is often 5-50% PV and the size of polymer is usually 50% PV.

Mechanisms:Lowering the IFT between oil and water

Solubilization of oil

Emulsification of oil

Mobility enhancement

Problems: expensive system, separation of chemicals is complex, high adsorption of surfactants, interaction between surfactant and polymer, chemical degradation at high temperatures

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Cont…


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Gravity >25 API

Viscosity <30 cp

Composition Light intermediates are desireable


Formation Sand stone is preferred

Permeability > 20 md

Depth < 8000 ft

Temperature < 175 F

Polymer flooding Polymer augmented waterflooding consists of adding water soluble polymers to the water before it is injected into the reservoir. The objective of polymer flooding is to provide better displacement and volumetric sweep efficiency during a waterflood.

Mechanism: Increasing the viscosity of water

Decreasing the mobility of water

Problems:

Lower injectivity that water

Acrylamide polymers lose viscosity with salinity

Xanthan gums are more expensive and are subject to microbial degradation

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Cont…


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Gravity >25 API

Viscosity <150 cp (preferably < 100 cp)

Composition Not critical




Depth about 9000 ft

Temperature < 200 F to minimize degradation

Alkaline flooding Alkaline or caustic flooding involves the injection of chemicals such as sodium hydroxide, sodium silicates or sodium carbonate. These chemicals react with crudes to produce insitu surfactants. They also react with reservoir rock to change wettability. The slug size is usually 10 to 50% PV.

Mechanism: IFT reduction

Changing wettability

Emulsification of oil

Solubilization of oil

Problems: high caustic consumption, scaling and plugging in carbonate reservoirs due the reaction with gypsum

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Cont…


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Gravity 13 to 35 API

Viscosity <200 cp

Composition Some organic acid is required

Oil saturation Above waterflood residual



Depth < about 9000 ft

Temperature < 200 F

In situ combustion In situ combustion or fireflood involves starting a fire in the reservoir and injecting air to sustain the burning of some of the crude oil. The most common technique is forward combustion in which the reservoir is ignited in an injection well and air is injected to propagate the combustion front away from the well.

Mechanism:Lowering the oil viscosity

Steam distillation and thermal cracking of crude oil

The pressure supplied to the reservoir by the injected air

Problems: complex and expensive process, non-environmental friendly process, corrosion by low pH hot water, sand production, pipe failure due to high temperature

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Cont…


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Gravity < 40 API

Viscosity <1000 cp

Composition Some asphaltic component

Oil saturation > 40-50% PV

Formation Sand stone


Depth > 500 ft

Temperature > 150 F

Additional notesPlease refer to:

1. J.J. Taber and F.D. Martin Technical Screening Guides for the Enhanced Recovery of Oil, SPE 12069.

2. J.J. Taber, F.D. Martin, R.S. Seright. EOR Screening Criteria Revisited- Part 1 : Introduction to Screening Criteria and Enhanced Recovery Field Projects, SPE-35385.

3. J.J. Taber, F.D. Martin, R.S. Seright. EOR Screening Criteria Revisited-Part 2: Applications and Impact of Oil Prices, SPE-39234.

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