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Petroleum Engineering Project Topics

A Case Study of Natural Flow and Tubing String Design for a Water Drive Reservoir

A Case Study of Natural Flow and Tubing String Design for a Water Drive Reservoir

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A Case Study of Natural Flow and Tubing String Design for a Water Drive Reservoir

Chapter One

OBJECTIVESย ANDย SCOPE OFย THEย WORK

Theย mainย objectivesย ofย thisย studyย include:

  • To design natural flow and artificial lift tubing strings for the whole life of a
  • To design and simulate along time the production conditions for natural flow, continuous liftand ESP for the later phases of the reservoir by imposing either a constant flowrate or aย constantย bottomย holeย flowing pressure.
  • To present a forecast of the production of oil and gas as well as the time where tubing strings should be replaced as a function of both the cumulative production and time.

Chapter Two

ย Literatureย Review

Theย Inflowย Performanceย Relationshipย (IPR)ย describesย theย behaviourย ofย aย wellโ€™sย flowingย pressure

andย productionย rate, whichย is an importantย tool inย understandingย theย reservoirย or well behaviourย andย quantifyingย theย productionย rate.ย Theย IPRย isย oftenย requiredย forย designingย wellย completion,ย optimizing well production, nodal analysis calculations, and designing artificial lift. Different IPRย correlationsย existย todayย inย theย petroleumย industryย withย theย mostย commonlyย usedย modelsย beingย thatย ofย Vogelโ€™sย andย Fetkovichโ€™sย (Mohammedย etย al,ย 2009).

RESERVOIRย NATURALย DRIVEย MECHANISMS

Natural drive mechanisms refers to the energy in the reservoir that allows the fluid to flow throughย theย porousย networkย andย intoย theย wells.ย Inย itsย simplestย definition,ย reservoirย energyย isย alwaysย relatedย toย someย kindย ofย expansionย (Cosentinoย etย al,ย 2001).ย Forย aย properย understandingย ofย reservoirย behaviour and predicting future performance, it is necessary to have knowledge of the drivingย mechanisms that control the behaviour of fluids within reservoirs. Several types of expansions takeย place inside and outside the reservoir, as a consequence of fluid withdrawals. Inside the reservoir,ย the expansion of hydrocarbons, connate water and the rock itself provides energy for the fluid toย flow. Outside the producing zone, the expansion of a gas cap and/or of an aquifer may also supply aย significant amount energy to the reservoir. In this case, the expansion of an external phase causes itsย influx into the reservoir and will ultimately result in a displacement process (Cosentino et al, 2001).ย There are basically six driving mechanisms that provide the naturalย energy necessary for oilย recovery:

  • Rock and liquid expansion drive
  • Depletion drive
  • Gas cap drive
  • Water drive
  • Gravity drainage drive
  • Combination drive

Theย attentionย ofย thisย projectย isย onย theย Depletionย driveย mechanismย alsoย knownย asย theย solutionย gasย drive mechanismย whichย is reviewed as follows.

SOLUTIONย โ€“ย GASย DRIVEย RESERVOIR

This driving form may also be referred to by the following various terms: Solution gas drive,ย Dissolvedย gasย drive orย Internal gasย drive.ย Aย solution gasย driveย reservoir isย oneย inย whichย the principalย drive mechanism is the expansion of the oil and its originally dissolved gas. The increase in fluidย volumes during the process is equivalent to the production (Dake, 1978). A solution โ€“ gas driveย reservoir is mostly closed from any outside source of energy, such as water encroachment. Itsย pressure is initially above bubble-point pressure, and, therefore, no free gas exists. The only sourceย of material to replace the produced fluids is the expansion of the fluids remaining in the reservoirย (Beggs, 2003). Some small but usually negligible expansion of the connate water and rock may alsoย occur.

When the reservoir falls below the saturation pressure, gas is liberated from the hydrocarbonย liquid phase. Expansion of the gasย phase contributesย to the displacement of the residual liquidย phase. Initially the liberated gas will expand but not flow, until its saturation reaches a thresholdย value, called critical gas saturation (Cosentino et al, 2001). Typical values of the critical saturationย ranges between 2 and 10% (Cosentino et al, 2001). When this value is reached, gas starts to flowย with a velocity proportional to its saturation. The more the pressure drops, the faster the gas isย liberated and produced, thus lowering further the pressure, in a sort of chain reaction that quicklyย leadsย to theย depletion of the reservoir (Cosentinoย etย al, 2001).

Atย theย surface,ย solutionย gasย driveย reservoirsย areย characterisedย inย generalย byย rapidlyย increasing in Gas โ€“ Oil Ratios (GORs) and decreasing oil rates. Generally no or little water isย produced.ย Theย idealย behaviourย ofย aย fieldย underย solutionย gasย driveย isย depletionย isย illustratedย inย fig.

2.3. The GOR curve has a peculiar shape, in that it tends to remain constant and equal to the initialย Rsi while the reservoir pressure is below the bubble point, then it tends to decline slightly until theย critical gas saturation is reached. This decline corresponds to the existence of some gas in theย reservoir, that cannot be mobilized (Cosentino et al., 2001). After the critical saturation is reached,ย the GOR increases rapidly and finally declines towards the end of the field life, when the reservoirย approachesย theย depletion pressure.

The most important parameter in solution โ€“ gas drive reservoirs is gas โ€“ oil relative permeability (Cosentino et al., 2001). Actually, the increase in the GOR curve is related to the increased gas permeability with respect to oil, as its saturation increases. The lower the critical gas saturation, the moreย rapidlyย theย gasย willย beย mobilisedย andย produced,ย thusย acceleratingย theย depletionย andย impairingย the finalย recoveryย (Cosentino etย al., 2001).

 

Chapter Three

Materialย Balanceย Forย Predictingย Theย Primaryย Recovery

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Tracyโ€™s calculations are performed in series of pressure drops that proceed from known reservoirย condition at the previous reservoir pressure p* to the new assumed lower pressure p. The calculatedย resultsย atย the new reservoirย pressureย becomeย โ€œknownโ€ย at theย next assumed lowerย pressure.

In progressing from the conditions at any pressure p* to the lower reservoir pressure p, consider thatย the incrementalย oilย and gas production areย โˆ†Npย and โˆ†Gp, or:

Nย pย =Nย p +ฮ”Nย p 3.1

Gย pย =Gย pย +ฮ”Gย p 3.2

where Nย pย ,Gย pย =ย ”ย knownย ”ย cumulative oilย and gas productionย atย previousย pressureย levelย p*

Nย pย ,Gย p =ย ”ย unknownย ”ย cumulativeย oilย andย gasย production atย newย pressureย levelย p

Chapter Four

Designย ofย Artificialย Liftย andย Tubingย Strings

ย DESIGN PARAMETER

Theย followingย dataย isย availableย forย theย oilย well:

Averageย reservoirย pressureย =ย 2740ย psiย Water Cutย = 0%

Initialย Gasย โ€“ย Liquidย ratioย (GLRi)ย =ย 721ย scf/stbย J* = 1.5

API =ย 25

Specific gravity to gas = 0.7ย Averageย Temperatureย =ย 170ย ยฐFย Reservoir depth = 7500 ftย Wellheadย pressureย =ย 150ย psi

Inclinationย angleย withย Horizontalย =ย 90oย (vertical well)

Nominalย tubing sizesย ofย 1/2โ€, 1โ€,ย 1ย 1/2โ€,ย 2ย 3/8โ€,ย orย 3ย 1โ„2โ€ย isย employedย inย theย design oftheย gasย lift.

CHAPTER FIVE

CONCLUSIONSย ANDย RECOMMENDATIONS

ย Conclusions

  • Reservoir pressure was maintained much longer in comparison to other drive mechanismwhen there is an active water drive preferably edge water drive reservoirs which maintains a steady-ย flowย conditionย for aย long timeย beforeย waterย breakthrough intoย the
  • In selecting the optimum tubing size both the hydrostatic loss and friction loss due to thetubing string must be carefully analysed. Optimum tubing string for the production of this reservoirย is the 2.375โ€ tubingย which produces the reservoir from an average pressure of 2740 psi at a GOR ofย 760ย scf/stbย up to aย pressureย of aboutย 1300 psi

Recommendations

Theย followingย areasย have beenย identifiedย forย improvementย inย theย developmentย ofย theย work

  • One of the assumptions in this work is the use of synthetic reservoir performance data basedon material balance a possible extension is by incorporatingย more practical condition byย including more wells andย theย performance with timeย betterย analysed
  • Furtheroilย productionย economicย analysisย shouldย beย inclusiveย inย theย workย soย thatย theย optimum productionย pattern of theย reservoirย willย beย determined

REFERENCES

  1. Beggs,,ย Productionย Optimizationย Usingย Nodalย Analysis,ย Secondย Edition,ย OGCIย andย Petroskillsย Publications,ย Tulsa,ย Oklahoma, pp.ย 150 –ย 153, 2003.
  2. Boyun, , Lyons, W. C., and Ghalambor, A., Petroleum Production Engineering, ElsevierScienceย andย Technologyย Books, 287 pp.,ย 2007.
  3. Craft,ย C.,ย andย Hawkins,ย M.,ย Appliedย Petroleumย Reservoirย Engineering,ย Secondย Edition,ย Prenticeย โ€“ Hall,ย Inc., New Jersey, pp. 370ย โ€“ 375, 1991.
  4. Cosentino,,ย Integratedย Reservoirย Studies,ย Technipย Editions,ย Paris,ย pp.ย 182ย โ€“ย 187,ย 2001.
  5. Dake,ย P.,ย Fundamentalsย ofย Reservoirย Engineering,ย Elsevier,ย Amsterdam,ย Theย Netherlands,ย 1978.
  6. Dake,ย P.,ย Theย Practiceย ofย Reservoirย Engineering,ย Revisedย Edition,ย Elsevier,ย pp.ย 86ย โ€“ย 109,ย 1994.
  7. Golan,,ย andย Whitson,ย C.ย H.,ย Wellย Performance,ย Secondย Edition,ย Prenticeย โ€“ย Hall,ย Inc.,ย 1995.
  8. Lyons,ย C.,ย Standardย Handbookย ofย Petroleumย &ย Naturalย Gasย Engineering,ย Vol.ย 1,ย Gulfย Publishing Company,ย Houston,ย Texas,ย 1996.
  9. Mohamed, E., Ahmed, E. H., Fattah, K. A., and El-Sayed, A. M. E., โ€œNew InflowPerformanceย Relationship for Solution-Gas Drive Oil Reservoirs,โ€ paper SPE 124041ย presented at theย 2009 SPE Annual Technical Conference and Exhibition held in Newย Orleans,ย Louisiana, USA, 4โ€“7 October
  10. Oudeman, P., โ€œOn the Flow Performance of Velocity Strings To Unload Wet Gas Wells,โ€paper SPE 104605 presented at the 15thย SPE Middle East Oil & Gas Show and Conferenceย heldย inย Bahrainย Internationalย Exhibitionย Centre,ย Kingdomย ofย Bahrain,ย 11ย โ€“ย 14ย March,

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