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Enhanced Oil RecoveryAlwyn project debriefing

Maria Aguilera

May 2013

EP - 22211_a_A_ppt_01 - EOR Introduction

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Slim tube simulations

Segment model

Water flooding

BO and compositional model comparison

Injector and producer completion optimization

Miscible Gas Injection

Water Alternating Gas Injection

Conclusions

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Slim tube simulationThe purpose of slim tube simulation is to investigate minimum miscibility pressure (MMP)between the reservoir oil and the injection gases. By knowing the MMP, we can ensure thatpressure will be maintained above MMP for gas injection process.

Slim tube (1D model) use in this project is composed of 500 grid cells with 1m of length in Xdirection and 10m in Y and Z direction. Injector is located in the first cell (1, 1, 1) andproducer is in the last cell (500,1,1).

EP - 22211_a_A_ppt_01 - EOR Introduction

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MMP determination: guidelines

EOS was already generated using the appropriate laboratory

experiments.

The fluid in place initially is only oil phase, no water present in slimtube.

MMP between oil-separator gas and oil-lean gas has already

determined. The simulation will only investigate MMP of oil-richgas and oil-CO2.

EP - 22211_a_A_ppt_01 - EOR Introduction

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Slim tube: model description

A very high permeability of the slim tube was used in order to

enhance mixing of the gas and the oil and also to reduce the effect ofthe viscosity gradient.

EP - 22211_a_A_ppt_01 - EOR Introduction

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MMP determination: CO2 injection

The simulation of CO2 injection was ran for different pressures ranging from 260 to320 bar. The table below shows the Initial Oil in Place (FOIP), AccumulativeProduction (FOPT) and the Recovery Factor (RF) as a result of injecting 1.2 PoreVolume (PV) of CO2 at pressures indicated

EP - 22211_a_A_ppt_01 - EOR Introduction

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MMP determination: rich gas injection

The simulation of rich gas injection was ran for different pressures ranging from 260to 340 bar. The table below shows the Initial Oil in Place (FOIP), AccumulativeProduction (FOPT) and the Recovery Factor (RF) as a result of injecting 1.2 PoreVolume (PV) of rich gas at pressures indicated,

EP - 22211_a_A_ppt_01 - EOR Introduction

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Viscous pressure gradient: CO2 injection

The pressure gradient after the gas breakthrough is noticed to be smaller becausethe gas has dissolved into the oil and the oil is lighter. Therefore, since the pressurein the cell depends on the fluid present, the lighter the fluid the less the pressure.

For the case after the gas breakthrough, the fluid in the slim tube is generallylighter.

EP - 22211_a_A_ppt_01 - EOR Introduction

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Viscous pressure gradient: rich gas injection

EP - 22211_a_A_ppt_01 - EOR Introduction

i

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MMP comparison

CO2 has the lowest MMP compared to rich gas and lean gas.

Separator gas which more or less has same composition as lean gashas the highest MMP.

Initial reservoir pressure is 446 bar which is higher than MMP of allthe gases inject, thus all the gases can be used for miscibleinjection.

To inject lean gas and separator gas, higher pressure maintenancein reservoir is needed.

In the paper SPE 37755, MMP is 375 bar, this value is between richgas and lean gas MMP. The volume of gas injection in SPE paper is1 PV and in this project we use 1.2 PV. There is not muchinformation of the gas injection composition in the paper to becompared with the gas composition in the project.

EP - 22211_a_A_ppt_01 - EOR Introduction

Ri h i j i d l

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Rich gas injection: desplacement process

Density plot before gas breakthrough: Miscibility region is located around blue line,The process is multiple contact miscibility with vaporizing mechanism behind the

miscible region and condensing mechanism after miscibility region.

EP - 22211_a_A_ppt_01 - EOR Introduction

Ri h i j ti di l t

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Rich gas injection: displacement process

Density and saturation plot of rich gas injection process at 298 bar (MMP) on grid number 250

1. Oil saturation (So) still at its initial because injected gas has not arrived,

2. After the injected gas reach grid 250, gas is dissolved in the oil and it lighten the oil (swelling) hence it reduce oildensity, then

3. Gas will act as a free gas,4. Vaporizing mechanismhappens when intermediates of the oil vaporize into the gas thus density-saturation of oil

decrease and density-saturation of gas increase,

5. Until it reach miscibility/near miscibility. In the miscibility region, density difference between oil and gas will be verysmall and composition of two fluids will be more or less the same.

6. After miscibility occurs, condensing mechanism happens. In this process, intermediate in gas will move into oilcause oil density increase and gas density decrease but gas saturation is kept increasing because more gas injectionarrive in the grid 250 and more oil is displaced by gas.

EP - 22211_a_A_ppt_01 - EOR Introduction

Ri h i j ti i it d i t f i l t i

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Rich gas injection: viscosity and interfacial tension

When miscibility occur, two fluids (gas and oil) will have similar component and itwill act as a 1 fluid thus the interfacial tension will decrease until zero. Oil viscositywill also decrease due to swelling.

EP - 22211_a_A_ppt_01 - EOR Introduction

CO2 injection: desplacement process

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CO2 injection: desplacement process

Density plot before gas breakthrough: Miscibility region is located around blue line,Although the profile is different, the process is multiple contact miscibility with

vaporizing mechanism behind the miscible region and condensing mechanism aftermiscibility region.

EP - 22211_a_A_ppt_01 - EOR Introduction

CO2 injection: displacement process

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CO2 injection: displacement process

Density and saturation plot of CO2 injection process at 286 bar (MMP) on grid number 250,compared with rich gas injection, miscibility on CO2 occur earlier. The process (steps 1 to 6)

is more or less the same as in rich gas injection.

EP - 22211_a_A_ppt_01 - EOR Introduction

CO2: viscosity and interfacial tension

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CO2: viscosity and interfacial tension

EP - 22211_a_A_ppt_01 - EOR Introduction

Slim tube test: gas breakthrough

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Slim tube test: gas breakthrough

Gas breaks through when free gas in reservoir is mobile (Sg > Sgc). Critical gassaturation in slim tube simulation is 0.075. In case of gas injection, gas in thereservoir is always mobile thus Sgc ~0. To know breakthrough time, look at GOR and

gas saturation in the last grid.

GBT for CO2 injection: 18 september 2015

GBT for rich gas injection: 17 november 2015

EP - 22211_a_A_ppt_01 - EOR Introduction

Gas saturation cross section for rich gas injection

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Gas saturation cross section for rich gas injection

EP - 22211_a_A_ppt_01 - EOR Introduction

Gas saturation cross section for CO2 injection

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Gas saturation cross section for CO2 injection

EP - 22211_a_A_ppt_01 - EOR Introduction