Oil Sand In-Situ Recovery Techniques

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OIL SAND & IT·S IN-SITURECOVERY TECHNIQUES



Oil Sand: Introduction

Definition: Contain naturally occurring mixtures of sand, clay, water and

bitumen (dense and extremely viscous form of petroleum) -

unconventional petroleum deposit.

Also called tar sands, crude bitumen or extra-heavy oil.

Global reserves: More than two trillion barrels of tar sands - largest

deposits being in Canada and Venezuela - tar sands represent about

40% of Canada's oil production.

API gravities range from 4° to 8°, easily the heaviest hydrocarbons

found ² Viscosity is so high that they do not flow at all at reservoirconditions; viscosity of Venezuela's Orinoco bitumen lies in the range

1000²5000 cP, while Canadian bitumen in the range 5000²10,000 cP.

World production rate of conventional crude will soon peak at an

estimated 27 billion bbl/year. Consequently, persistent demand will

encourage more permanent and economically stable development of oilsand production.



Problem Definition

Extraction from oil sand reserves is very complex andexpensive. This is especially true in case of in-siturecoveries, since mining operation is relatively simpler

but can be carried out only in shallow reservoirs, usuallyat depths lesser than 50 -75 m. For deeper deposits,the only convenient option available is in-situ recovery.

Since the energy required and cost involved in thevarious in-situ recovery techniques are of enormous

proportions, it becomes highly imperative that the mostsuitable as well as economical production technique isselected for implementation in the given field.



Production & Processing

Oil sand extraction done by: (i) mining (ii) in-situ recovery.

Methods for in-situ production include:

Cyclic steam stimulation (CSS)

Steam Assisted Gravity Drainage (SAGD)

In-situ combustion

Toe to Heel Air Injection (THAI)

Tar/oil sands processed to generate oil similar to conventional crudeoil - more complex and expensive.

Processing includes: (i) separation of bitumen from the otherconstituents like clay, sand and water (ii) bitumen upgrading beforerefining - being highly viscous, bitumen also requires dilution withlighter hydrocarbons to make it transportable via pipelines.



In-situ Combustion



In ² Situ Combustion

Involves generation of heat by combustion within the

reservoir.

Requires 2 vertical wells ² 1 injector & 1 producer.

Air or oxygen is injected into the injected wells to

sustain the combustion front.

As the combustion front advances through the

reservoir, the oil ahead of the front becomesheated and reduces the viscosity of native reservoir

by transferring the heat and mixing of flue gas.



Mechanism

The mechanism of in-situ Combustion indecreasing order is as follows:

Flue gas sweeping

Field re-pressurization

Oil swelling

Viscosity reduction

Stripping of light oil components of oil

Thermal effect



Mechanism

When air is injected into an oil reservoir, two simultaneousphenomena occur: displacement of oil and oxidation of oil.

According to the efficiency of displacement and the intensity ofoxidation, four main types of processes can occur.

1. Immiscible Airflooding (IAF) with High Temperature Oxidation(HTO)

2. IAF with Low Temperature Oxidation (LTO)

3. Miscible Airflooding (MAF) with HTO

4. MAF with LTO

For heavier crude oils or tar sands, heat and steam generationand subsequent viscosity reduction is the primary oil displacementmechanism.

For this reason, in-situ combustion in a heavy oil reservoir shouldoperate in the high temperature oxidation reaction regime.



Reservoir Parameters suitable for in-situ

combustion

Oil Content : High oil saturation & low water saturation

required.

Pay thickness : between 5 ft. - 50 ft. Generally thickness

greater than 10 ft is desired to prevent excessive heat loss. Depth : > 200 ft.

Oil gravity & viscosity : between 100 - 400 API

Reservoir Permeability greater than 100md allows more flow

of viscous oil. Size of Reservoir : 100 acres(min.)

Reservoir Confinement : No gas cap or water zone.



Advantages of in-situ combustion

Universal availability of air

Applicable in wide range of reservoir

High swept efficiency with thermal front

Economically and environmentally favorable

Reservoir pressurization

Improvement in viscosity and density contrast between theresidence oil and water.

It is the ideal process for producing oil from thin formation.

Formation permeability has minimal effect on this process Can be applied to a reservoir which has already undergone

water flooding or steam flooding

Can be applied in both heavy and light oil reservoirs.



Limitations of in-situ Combustion

Oil saturation and porosity must be high enough so thatheat loss to the rock will minimize.

Not applicable in fracture reservoir because early

breakthrough may happen. Oil sweeping process takes place in upper part of the

layer hence, sweep efficiency is poor in thick reservoir.

Requires more controlled process of air injection rate or

flux.



THAI� Process



THAI� Process

The THAI� process uses horizontal production wells paired

with vertical air injection wells to recover bitumen.

Horizontal production wells are drilled to the desired depth.

Air injection wells are drilled to the ¶toe· of the horizontal wells. Steam is injected through the vertical and horizontal wells for

up to three months to heat the oil sands reservoir.

Once the reservoir reaches the required temperature and

mobility, air is injected into the formation through the airinjection well. When oxygen in the air contacts the heated oil

sands, a combustion reaction starts.



THAI� Process

As additional air is injected into the formation, thecombustion front moves slowly from the toe to the heelof the horizontal production well, partially upgradingthe bitumen, producing THAI� oil.

The THAI� oil, along with water and gases that areproduced during combustion (primarily nitrogen andcarbon dioxide), drain into the horizontal well.

Once at the surface, the produced fluids are treatedand the THAI� oil is sent to market.



Suitable reservoir parameters used to

model the THAI� process

Oil Saturation = 50% - 80%

Oil Quality = 8° API or greater

Oil Viscosity At Reservoir Temp. = <250,000 cP

Vertical Permeability = 0.5 D Net Pay = >10m

Shale Content = Shale breaks are not expected to beproblematic

Clay Content = Clay is beneficial to catalyze crackingupgrading reactions.

Thief Zones = Not expected to be problematic



THAI� Advantages

The THAI� process offers a number of potentiallysignificant resource, economic and environmentalbenefits when compared to other in situ oil sandsrecovery processes, including:

Increased resource recovery Production of a partially upgraded bitumen product

Reduced natural gas use

Less water production

Reduced diluents requirements Reduced greenhouse gas emissions and Smaller surface

footprint.

Lower capital and operating costs.

Oil Sand In-Situ Recovery Techniques

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