Immiscible Oil Displacement

05/12/13

Oil Recovery There has been two processes developed for

CO2-EOR: Miscible Displacement Immiscible Displacement

Immiscible displacement of oil by CO2 is done by mostly gravity stable gas injection (GSGI) method and immiscible water alternating gas (IWAG).

What is GSGI?

Gravity stable gas injection (GSGI) is a method of introducing CO2 in the reservoir by injecting it in the crest, forcing the oil to move downwards and to the direction of the rim, where the producing wells are located.

In GSGI method, the CO2 is not necessarily immiscible to oil.

CO2 is used for maintaining reservoir pressure and for stabilizing displacements via gravity drainage to increase sweep.

Why Do Immiscible CO2-EOR? Injection of CO2 in a reservoir can still increase oil

recovery even when MMP is not reached.

It should be done in cases where the reservoir pressure is too low to reach the MMP.

Immiscible oil displacement works by increasing the reservoir pressure to force the oil towards the well and by some oil swelling and viscosity reducing effects.

Miscible Displacement is not a “Holy Grail”!

Mechanism of Immiscible CO2 EOR

According to research done to immiscible CO2 EOR, it is reported that the following mechanisms occur during the process: Oil viscosity reduction Oil expansion (swelling) Interfacial reduction Blow down recovery

Increase the mobility of oil; depends on P, T and oil composition

A mechanism when the pressure decrease, CO2 will come out of the solution while sweeping the oil of the wellbore

The Techniques: CO2 Flooding CO2 injected in GSGI mode (typically) at slow rates at

the crest of the reservoir aiming at filling the pore volume of the reservoir rock.

The injected gas creates an artificial gas cap, pushing oil simultaneously downwards and towards the rim of the producing wells.

Presence of water reduce

the effectiveness of

the process

CO2 + Water + Asphaltene precipitation!

The Techniques: Immiscible WAG The portion of injected CO2 dissolved (partially) in

the oil reduces the oil viscosity and in addition, swells the oil.

The process is then followed by waterflooding of the reduced viscosity oil.

Injecting the immiscible gas alternately with water reported to result a better sweep by the injected gas and therefore improved recovery over injection of the gas as a slug.

This method is less favored on reservoir with high heavy oil content

Immiscible CO2 EOR Cases Bati Raman Oil Field (Turkey, 2005-present)

• The oilfield contains heavy oil with very low gravity (9o to 15o API). CO2 comes from a nearby natural reservoir.

• Traditional oil recovery techniques yielded only 1.5% of the OOIP while through EOR about 6.5% of OOIP is estimated to be recovered.

• Injection of CO2 has caused oil swelling, despite the lack of miscibility, reducing the viscosity of oil by a factor of 10.

• Approximately 1700 tons of CO2 are injected daily, 16 to 60% is recycled.

Immiscible CO2 EOR Cases Weeks Island (USA, 2005)

• Failed due to the presence of high pressure aquifer that did not permit the displacement of oil upon injection.

• Pilot project managed to yield 60% of oil left after water flooding.

Hungary (1980-1990s)• EOR was achieved by creating an artificial gas cap of CO2.

• Overall CO2 utilization was 380 m3 per barrel of oil extracted.

Lessons Learnt Experience has shown that the conditions that favor

immiscible displacement include• High vertical permeability in the reservoir rock.• A substantial amount of oil to form a thick oil column.• A steeply dipping relief and good lateral and vertical

communication through the reservoir.• Absence of fractures that reduce sweep efficiency.

It has been estimated that:• The utilization of CO2 is within the range 280-400 m3 of

CO2 per barrel of incremental oil (560-790 kg/bbl).

• The process may yield approximately up to 20% of OOIP.

Miscible vs Immiscible CO2 EOR Compared to miscible CO2 EOR, immiscible CO2

EOR is less researched.

Evolution of the number of CO2-EOR projects and their cumulative production in the USA

Miscible vs Immiscible CO2 EOR With assumptions of miscible projects are brought

by WAG and immiscible projects by GSGI, the following comparison can be concluded:

The Up-Down(s) of Immiscible CO2 EOR The Downs:

- Huge amounts of CO2 are required- Additional oil production is very slow- Limiting opportunities for smaller scale

implementation

The Up:- High potency of carbon sequestration.

EOR vs Carbon SequestrationV

olu

me

of

CO

2

Time

EOR

Brine sequestration

EOR• Significant volumes: only a fraction of all

point source CO2 can be sold for EOR

• Offset some of cost of capture and pipeline development

• Will help grow and develop needed technologies

• Will increase public acceptance

Modified from Hovorka, 2010