ADDITIONAL OIL RECOVERY BY ADDITIONAL OIL RECOVERY BY GAS RECYCLINGGAS RECYCLING

Syed Muhammad Raza Qasim Taqvi (Group Leader)07PG132

Syed Najaf Akhtar Zaidi (Assistant Group Leader) 07PG48

Muhammad Shoaib Khan 07PG135

Muhammad Fahad 07PG131

Ali Arsalan Pathan07PG134

Junaid Ishtiaque 07PG52

Agenda & DistributionAgenda & Distribution INTRODUCTION

Ali Arsalan Pathan

OTHER MISCIBLE METHODS Muhammad Fahad

CLASSIFICATION OF GAS RESERVOIRS & PRESSURE MAIINTAINANCE IN CONDENSATE RESERVOIR

Junaid Ishtiaque

OVERVIEW OF CONDENSATE RESERVOIR & ITS PRODUCTION HANDLING

Muhammad Shoaib Khan

THERMODYNAMICS OF GAS RECYCLING & WELL LOCATION Syed Najaf Akhtar Zaidi

CASE STUDY S M Raza Qasim Taqvi

IntroductionIntroductionBy Ali Arsalan Pathan

IntroductionIntroductionWorldwide reservoirs are

depleting…..so the need of today is to find more oil deposits or other resources of energy….◦ Cure the reservoirs…??

Curing methods… IOR EOR

For the peculiar Gas Condensate Reservoir….. Most suitable method is “GAS RECYCLING”

Gas RecyclingGas RecyclingThe re-injection of the produced gas

back into the reservoir is called GAS RECYCLING

It can be carried out in initial as well as later stages of the field

Gas recycling maintains the reservoir pressure and allowing it to decline the pressure slowly and gradually!!!

What is the basic purpose to choose this method…?

To debate…

Gas Recycling Gas Recycling (Continue…)(Continue…)Gas Recycling in gas condensate Reservoir

has been recommended for several years as an optimum production scenario of increasing condensate recovery

As pressure reduces, liquid condenses from the gas to form free liquid in the reservoir

Condensate liquid builds up near wellbore causing a reduction in gas permeability and gas productivity………required additional oil recovery….by….GAS RECYCLING

The injection of Dry gas into gas condensate reservoir helps in vaporizing the condensate and increase its dew point

What is the future of this technique??

Other Miscible MethodsOther Miscible MethodsBy Muhammad Fahad

Miscible MethodsMiscible MethodsThe gas miscible methods are

……MISCIBLE HYDROCARBON

DISPLACEMENTCARBON DIOXIDE INJECTIONINERT GAS INJECTION

MISCIBLE HYDROCARBON MISCIBLE HYDROCARBON DISPLACEMENTDISPLACEMENT

A Dissolving fluid will be introduced into the reservoir to eliminate the forces causing oil retention and helps in sweep efficiency.

In earlier days a solvent was injected followed by liquid or gas but the result are not effective.

MISCIBLE HYDROCARBON MISCIBLE HYDROCARBON DISPLACEMENTDISPLACEMENT

MISCIBLE SLUG PROCESS: A slug of liquid hydrocarbon equivalent to 50% PV followed by natural gas, or gas and water is injected.

ENRICH GAS PROCESS: A slug of enriched natural gas followed by lean gas is injected with the ration ranges between 10-20% PV consist of ethane through hexane (C2-C6).

HIGH PRESSURE LEAN GAS PROCESS: A lean gas is injected at a high pressure in order to cause retrograde evaporation of the crude oil and formation of a miscible phase, which contain C2-C6.

CARBON DIOXIDE INJECTIONCARBON DIOXIDE INJECTION CO2 is forced into a reservoir which create a miscible

front by a gradual transfer of smaller, lighter hydrocarbon molecules from the oil to the CO2.

This miscible front is a essence a bank of enriched gas.

Under favorable conditions this front will be soluble with the oil, making it easier to move toward production wells

Production comes from an oil bank that forms ahead of the miscible front.

As reservoir fluids are produced through production wells, the CO2 reverts to a gaseous state and provides a "gas lift" similar to original reservoir pressure

This procedure may be repeated until oil production drops below a profitable level.

CARBON DIOXIDE CARBON DIOXIDE INJECTIONINJECTION

ADVANTAGES

Swells oil and reduces viscosity.

Miscibility can be attained at relatively low pressure in many reservoirs.

Carbon dioxide is a non-hazardous, non-explosive gas that causes no environmental concern if large quantities are lost to the atmosphere.

May be available as a waste gas (gas-processing plants or industrial plants) or may be produced from reservoirs containing CO2.

DIS-ADVANTAGES

Injection of slugs of water is often necessary to reduce fingering.

Carbon dioxide with water forms highly corrosive carbonic acid. Special metal alloys and coatings for facilities are needed. Corrosion mitigation can be a considerable part of the cost of the process.

The alternate injection of slugs of CO2 and water requires a dual injection system, adding to the cost and complexity of the project.

Large volumes of CO2 are needed. It may take 5-10 MSCF of gas to produce one barrel of stock tank oil.

INERT GAS INJECTIONINERT GAS INJECTIONNITROGEN is injected into a reservoir forms a miscible front

by vaporizing some of the lighter components from the oil.

This gas, now enriched to some extent, continues to move away from the injection wells, contacting new oil and vaporizing more components, enriching itself further, this action continues, the leading edge of this gas front becomes so enriched that it goes into solution becomes miscible, with the reservoir oil.

Continued injection of nitrogen pushes the miscible front through the reservoir moving a bank of displaced oil toward production wells

Water slugs are injected alternately with the nitrogen to increase the sweep efficiency and oil recovery

Produced reservoir fluids may be separated for the oil , natural gas liquids and N2

INERT GAS INJECTIONINERT GAS INJECTION

ADVANTAGES

• Nitrogen can be manufactured on site at less cost than other alternatives

Nitrogen has an unlimited source, and being completely inert it is non-corrosive

DIS-ADVANTAGES

• Reservoir should have API gravity higher than 35 degrees

• The oil should have a high formation-volume

• The oil should be under saturated or low in methane (C1).

• The reservoir should be at least 5,000 feet deep to withstand the high injection pressure (in excess of 5,000 psi) necessary for the oil to attain miscibility with nitrogen without fracturing the producing formation

CLASSIFICATION OF GAS RESERVOIRS & CLASSIFICATION OF GAS RESERVOIRS & PRESSURE MANTAINANCE IN PRESSURE MANTAINANCE IN CONDENSATE RESERVOIRCONDENSATE RESERVOIR

By Junaid Ishtiaque

TYPES OF GAS TYPES OF GAS RESERVOIRSRESERVOIRS If the reservoir temperature is above the critical

temperature of the hydrocarbon system, the reservoir is classified as a natural gas reservoir. On the basis of their phase diagrams and the reservoir conditions, natural gases reservoir can be classified into four categories:

Retrograde gas-condensateNear-critical gas-condensateWet gasDry gas

PRESSURE MAINTENANCE IN OIL PRESSURE MAINTENANCE IN OIL RESERVOIR BY GAS INJECTIONRESERVOIR BY GAS INJECTIONINTRODUCTION AND BACKGROUNDINTRODUCTION AND BACKGROUND

INTRODUCTION Physical criteria for successful gas

injection operation are basically the same as for type of fluid injection the same physical and thermodynamics variable control the displacement process

Gas injection has been used-to maintain reservoir pressure at some selected level or to supplement natural reservoir energy to a lesser degree by re-injection of a portion of the produced gas

Gas injection has also been employed frequently to prevent migration of oil into a gas cap in oil reservoir with natural water drives, with down dip water injection or both.

BACKGROUND Since 1978 and the passage of the

Natural Gas Policy Act, the increasing value of sales gas resulted in a decline in the number of new gas-injection projects. However, some opportunities still exist in remote areas where recovery consideration are augmented by storage aspect of such projects and by specialized application in connection with gravity drainage systems and attic oil recovery projects.

TYPES OF GAS -INJECTION TYPES OF GAS -INJECTION OPERATIONOPERATION Gas-injection pressure maintenance operations are generally

classified into two distinct types depending on where in the reservoir, relative to oil zone, the gas is introduced.

TWO TYPES OF GAS –INJECTION OPERATIONS:

1. External gas injection: External gas injection operation frequently referred to as crestal or gas cap injection use injection wells in structurally higher positions of reservoir usually in primary or secondary gas cap

2. Dispersed Gas Injection: Dispersed gas injection operations frequently referred to as internal or pattern injection normally used some geometric arrangement of injection wells for the purpose of uniformly distributing the injection gas throughout the oil productive portions of reservoir

OIL RECOVERY EFFICIENCIESOIL RECOVERY EFFICIENCIES1.Unit Displacement Efficiency: Unit displacement efficiency is the percentage of oil in place

within a totally swept reservoir- rock volume that is recovered as a result of the displacement process

2. Conformance Efficiency: Conformance efficiency is the percentage of the total rock or

pore volume within swept area that is contacted by displacing fluid.

3. Areal sweep efficiency: Areal sweep efficiency is the percentage of total reservoir or

pore volumes that is Within swept area, the area contacted by displacing fluid.

Each of the three efficiencies increases with continued displacement, therefore,' each is a function of number of displacement volumes, injected .The rate of increase in recovery efficiency in a -given portion of reservoir diminishes as gas break through occurs. Therefore the maximum value of each component efficiency and, consequently ultimate recovery efficiency is limited by economics considerations.

CALCULATION OF GAS PRESSURE CALCULATION OF GAS PRESSURE MAINTENANCE PERFORMANCEMAINTENANCE PERFORMANCE

Estimate of gas-injection performance are generally based on simultaneous solution of one more forms of conventional material-balance equation and displacement equation

A complete engineering analysis of reservoir for purpose of evaluating gas-injection operations will usually consist of four major phases:

Assembly, preparation, and analysis of basic data'; Analysis of past performance, Projection of future performance of current operations, and, Estimation of gas pressure maintenance performance,

Overview of Gas Condensate Overview of Gas Condensate Reservoir & its Production Reservoir & its Production HandlingHandlingBy Muhammad Shoaib Khan

Overview of Gas Condensate Overview of Gas Condensate ReservoirReservoir

That contains fluids only as a gas phase under initial reservoir T &P.

• Condensate separate from gas in a process called retrograde condensation.

• What happens to the particles of a gas when they condense?

• Why do we need gas recycling process ?

• Why methane is good for gas recycling?

• What is composition of gas condensate reservoir?

Continue Gas condensate reservoir…Continue Gas condensate reservoir…

How does Gas condensate reservoir develop?

By producing the reservoir by natural depletion. The produced fluids are processed and the resulting dry gas and gasoline sold.

By rejection of all or part of the dry gas produced back into the reservoir. The attractiveness of this recycling technique depends on the particular circumstances and on how the recycling is carried out.

Pressure and Temperature Ranges of Gas-Condensate Reservoirs are:◦ Gas-condensate reservoirs may occur at pressures below

2,000 psi and temperatures below 100°F

◦ Probably can occur at any higher fluid pressures and temperatures within reach of the drill.

◦ Most known retrograde gas-condensate reservoirs are in the range of 3,000 to 8,000 psi and 200 to 400°F.

Continue Gas condensate Continue Gas condensate reservoir…reservoir…

•Formation GOR• 5000 - 10000 scf/bbl

•What are the virtue exist in gas condensate reservoir for Pressure maintenance?

• An active water drive• water injection operations• Injection of gas• combination of all of these.

•What are the data Requirements for gas-condensate cycling study?

(1) Geologic data (2) Physical properties of the reservoir rock (3) Fluid characteristics (4) Reservoir pressure history (volumetrically weighted) from discovery to present (5) Condensate, gas, and water production data, from the date of discovery (6) Proposed future production rates (7) Gas- and/or water-injection data, past and future (8) Productivity, injectivity & Backpressure test data on wells.

Handling of ProductionHandling of Production Main Equipment Separator , Compressor & fractionation equipment.

Desulphurization: Reagents used:Sodium carbonate solution (regeneration by air

current).Sodium phenolate (regeneration by heating),Amines (regeneration by heating).

Dehydration: Various desiccants are used, both solids (silica gel, activated

aluminum, calcium sulphate, anhydrite, fluorite, etc.) and liquids (glycols). There is practically no economic method for the removal of oxygen from gas.

Filtration: Injection gas must be free from solid or liquid particles.

Scrubbers and filters are thus installed in the system so as to remove all particles larger than a few microns.

Thermodynamics of Gas Thermodynamics of Gas Recycling and well Recycling and well locationlocationBy Syed Najaf Akhtar Zaidi

THE THERMODYNAMICS OF GAS THE THERMODYNAMICS OF GAS RECYCLINGRECYCLING

Gas recycling may take place either:At a pressure higher than or equal to the dew-

point pressure pd.At a pressure lower than the dew-point.The idea of Thermodynamics of gas recycling is

being given by Standing in 1952.Re-injection of high pressure gas could be used to

vaporize crude oil and then be displaced by cycling as gas phase.

This helps to maintain or restore the reservoir pressure in order to increase the ultimate oil recovery.

WELL LOCATIONSWELL LOCATIONS Developed field: In which gas recycling starts after long

period of natural depletion

Undeveloped field: By model study well arrangements are then selected.

pattern flooding Objective……. To select a proper pattern that will provide the Injection fluid with the maximum possible contact with the

crude oil system.Types:

◦ Direct line drive◦ Stagerred line drive◦ Five spot◦ Seven spot / inverted seven spot( 1 injector + 6 producers)◦ Nine spot

INJECTION ZONEINJECTION ZONE Gas injection into a gas-cap; when a gas-cap originally exist in

a reservoir or when it is formed by segregation during primary production.

Gas injection into an oil zone; without presence of a gas-cap the injected gas radially flows from the production wells.

There are certain conditions under which water injection should not be considered:

(a) A very extensive gas-cap may form a preferential path for injected water which will thus by-pass the oil zone. By comparison, gas injection into the gas cap may result in additional oil recovery for the price of a few gas injection wells.

(b) A reservoir with a high initial water saturation may not be suitable for water injection. There is a risk that no front will be formed and that oil and water will flow in parallel, giving a low recovery efficiency.

If the reservoir has sufficiently high vertical permeability, gas-cap injection will result in higher recovery than injection into the oil zone. The area at the gas-oil contact is large, whereas in radial displacement the area of contact bet ween gas and oil is initially small.

The capacity of each injection well can be estimated using an equation of the well-known form: Q=C(P2

IW –P2e)n

Case StudyCase StudyBy S M Raza Qasim Taqvi

Case studyCase studyRecommended field

Kunnar oilfield and LPG plant

Interesting point….initial feed upStarted date of project 1998

Started date of Gas recycling

2000

NO: of production well 6

No: of Gas injection well 1 (1-A)

Injection pressure 1650-1750

Ni 31.6 MM BBLS

Gi 124 BCF

Flow Rate before and afterFlow Rate before and after

WHFB Before & After WHFB Before & After InjectionInjection

Table of Flow Rate Table of Flow Rate Showing Decline In 2 YearShowing Decline In 2 Year

Declining of Flow Rate in 2 Declining of Flow Rate in 2 YearsYears

0.96 1.2

6.12

0.432

2009

2011

2009

Comparison of Decline Rate Comparison of Decline Rate in 2 Years in 2 Years

ConclusionConclusion IOR from gas injection has in the long run proved

more economical than expected Considering the huge amount of gas currently being

flared, gas re-injection is a fast and valuable alternative to avoid flaring and thereby reduce CO2 emission and safe the environment

Gas Recycling is a well know method of storing gas instead of flaring

The initial decline in a pressure and flow rate will be easily maintained

The recovery of condensate may be increased to a greater level by utilizing the gas, that comes out of the same well

Many fields of OGDCL specially chanda, bobi, can use that techniques to optimize their oil production. Such like; bobi field is also using Gas re-injection. Gas Condensates fields are the most suited field for this operation

References References The development study on gas recycling injection in Yaha

Gas Condensate Field, Tarim Basin, China Effect of Gas Recycling on the Enhancement of Condensate

Recovery, Case Study: Hassi R’Mel South Field, Algeria Energy Information Administration:”U.S. Crude Oil, Natural

Gas, and Natural Liquids Reserves 2002 Annual Report:. December 2003

Moritis, G.:”EOR Continues to Unlock the Oil Resources”, Oil & Gas journal ,pp.45-52 April12,2004.

Simulation of Experimental Gas-Recycling Experiments in Fractured Gas/Condensate Reservoirs

Kenyen.D and behei.: Third SPE comparative Project: Gas cycling of retrograde condensate reservoir, SPE Paper 12278, Journal of petroleum technology p 981-997, Aug, 1987.a

Trans AIME Ballard,J.R. and Smith, L.R.” Reserves Engineering Design of a Law Pressure Rich Gas Miscible Slug Flood:Jour Pet .Teach

References (Continue...)References (Continue...) Gao, J., Zheng,D. and Guo, T.: “ Solubility of Methane, Nitrogen, Co2 and

a Natural gas mixture in Aqueous Sodium Bicarbonate Solutions under High Pressure Elevated Temperature”, J.Chem.Eng.Data, Vol.42, p 69-73, 1997.

Fundamental of Enhanced Oil Recovery by Jacques Hagoort Applied Reservoir Engineering by B.C Craft and M.F.Hawkins Petroleum Engineering Hand Book-II by Howard B.Bradly Stalkup, F.I.: “ Miscible Displacement”, SPE Monograph Series, New

York, p.129. Oil Reservoir Engineering Hand Book by G.Georege Segeler Mechanics of Secondary Oil Recovery by Charles Robert Smith Fundamental of Reservoir Engineering by L.P.Dake Enhanced Oil Recovery by Marcel Latil Reservoir Engineering HandBook By Tarek Ahmed WEBSITES: http://www.tutorvista.com/chemistry/realgases http://www.springerlink.com/index/h75555775817076.pdf http://www.rigzone.com/training/insight.asp?insight_id=345&c_id=4 http://www.naturalgas.org.com http://www.pet.hw.ac.uk/research/rfi/index.htm