IPR Methods

7/22/2019 IPR Methods

1/48

Reservoir Engineering

1

Course (

1

st

Ed.)
http://www.about.me/AlamiNiamailto:[email protected]://www.about.me/AlamiNiamailto:[email protected]


2/48

1. Productivity Index (PI)

2. Inflow Performance Relationship (IPR)

3. Generating IPR

A.

Vogel

s Method

B.

Vogel

s Method (Undersaturated Reservoirs)


3/48

1. Future IPR Approximation

2. Generating IPR for Oil Wells

A.

Wiggins

Method

B. Standin

g

s Method

C. Fetkovi

ch

s Method

3. Horizonta

l Oil Well Performance

4.

Horizontal Well Productivity


4/48


5/48

IPR PredictionQuite often it is necessary to predict the wells

inflow performance for future times as thereservoir pressure declines.

Future well performance calculations require thedevelopment of a relationship that can be used topredict future maximum oil flow rates.

Several methods are designed to address the

problem of how the IPR might shift as the reservoirpressure declines.

2013

H. AlamiNia Reservoir Engineering

1

Course: IPR Methods for Vertical Oil Wells / Horizontal Well 5


6/48

IPR Prediction Cont.)Some of these prediction methods require the

application of the material balance equation togenerate future oil saturation data as a function ofreservoir pressure.

In the absence of such data, there are two simpleapproximation methods that can be used in conjunctionwith Vogels method to predict future IPRs.

2013

H. AlamiNia Reservoir Engineering

1

Course: IPR Methods for Vertical Oil Wells / Horizontal Well 6


7/48

IPR Prediction:1st Approximation MethodThis method provides a rough approximation of the

future maximum oil flow rate (Qomax)f at thespecified future average reservoir pressure (pr)f.

This future maximum flow rate (Qomax) f can be used inVogels equation to predict the future inflowperformance relationships at (pr)f.

2013 H. AlamiNia Reservoir Engineering 1 Course: IPR Methods for Vertical Oil Wells / Horizontal Well 7


8/48

IPR Prediction:1st Approximation Method Cont.)Step 1. Calculate (Qomax)f at (pr)f from:

Where the subscript f and p represent future andpresent conditions, respectively.

Step 2. Using the new calculated value of (Qomax)fand (pr)f, generate the IPR by:



9/48

IPR Prediction:2nd Approximation MethodA simple approximation for estimating future

(Qomax)f at (pr)f is proposed by Fetkovich (1973).The relationship has the following mathematicalform:

Where the subscripts f and p represent future and

present conditions, respectively.The above equation is intended only to provide a rough

estimation of future (Qo)max.



10/48


11/48

Wiggins MethodWiggins (1993) used four sets of relative

permeability and fluid property data as the basicinput for a computer model to develop equations topredict inflow performance.

The generated relationships are limited by theassumption that the reservoir initially exists at itsbubble-point pressure.



12/48

Wiggins Method Cont.)Wiggins proposed generalized correlations that are

suitable for predicting the IPR during three-phaseflow.

His proposed expressions are similar to that ofVogels and are expressed as:



13/48

Vogels vs. Wiggins IPR Curves



14/48


15/48

Standings MethodStanding (1970) essentially extended the

application of Vogels to predict future inflowperformance relationship of a well as a function ofreservoir pressure.

He noted that Vogels equation can be rearrangedas:

Standing introduced the productivity index J asdefined by J=Qo/ ((pr)-pwf) into above Equation toyield:



16/48

StandingsZero-Drawdown Productivity IndexStanding then defined the present (current) zero

drawdown productivity index as:

Where J*p is Standings zero-drawdownproductivity index. The J*p is related to theproductivity index J by:

J=Qo/ ((pr)-pwf) Equation permits the calculationof J*p from a measured value of J.



17/48

Standings Final Expressionfor IPR PredictionTo arrive at the final expression for predicting the

desired IPR expression, Standing combinesEquations to eliminate (Qo)max to give:

Where the subscript f refers to future condition.



18/48

Standings DrawdownProductivity Index J*P)Standing suggested that J*f can be estimated from

the present value of J*p by the followingexpression:

Where the subscript p refers to the presentcondition.

If the relative permeability data are not available,

J*f can be roughly estimated from:



19/48

Summary of Standings MethodStandings methodology for predicting a future IPR

is summarized in the following steps:

Step 1. Using the current time condition and the

available flow test data, calculate (Qo)max fromEquations below.

Step 2. Calculate J* at the present condition, i.e.,J*p.



20/48

Summaryof Standings Method Cont.)Step 3. Using fluid property, saturation, and relative

permeability data, calculate both (kro/oBo)p and(kro/oBo)f.

Step 4. Calculate J*f by using below Equation. Usethe other equation if the oil relative permeabilitydata are not available.

Step 5. Generate the future IPR by applying belowequation.



21/48

Disadvantagesof Standings MethodologyIt should be noted that one of the main

disadvantages of Standings methodology is that:

It requires reliable permeability information;

In addition, it also requires material balance calculationsto predict oil saturations at future average reservoirpressures.

It should be pointed out Fetkovichs method hasthe advantage over Standings methodology

In that, it does not require the tedious material balancecalculations to predict oil saturations at future averagereservoir pressures.



22/48


23/48


24/48

Fetkovichs MethodMuskat and Evinger (1942) attempted to account

for the observed nonlinear flow behavior (i.e., IPR)of wells

by calculating a theoretical productivity index from thepseudosteady-state flow equation.

They expressed Darcys equation as:



25/48

Pressure Function Concept



26/48

Fetkovichs Method: 1st CaseIn the application of the straight-line pressure

function, three cases must be considered:

Case 1: pr and pwf > pb

Where Bo and o are evaluated at (pr+ pwf)/2.

Case 2: pr and pwf < pb

Case 3: pr > pb and pwf < pb



27/48

Fetkovichs Method:2nd Case, Present IPRThe term (J/2pb) is commonly referred to as the

performance coefficient C, or:

To account for the possibility of non-Darcy flow (turbulent flow)in oil wells, Fetkovich introduced the exponent n to yield:

The value of n ranges from 1.000 for a complete laminar flow to0.5 for highly turbulent flow.



28/48

Fetkovichs Method:2nd Case, Calculation of C and NThere are two unknowns in the Equation:

The performance coefficient C and the exponent n.

At least two tests are required to evaluate these twoparameters:

A plot of p2r p2wf versus Qo on log-log scales will result in astraight line having a slope of 1/n and an intercept of C at p2rp2wf = 1.

The value of C can also be calculated using any point on thelinear plot once n has been determined to give:



29/48

Fetkovichs Method:2nd Case, Future IPRTo construct the future IPR when the average

reservoir pressure declines to (pr)f,

Fetkovich assumes that the performance coefficient C isa linear function of the average reservoir pressure and,

Therefore, the value of C can be adjusted as:

Fetkovich assumes that the value of the exponent n would notchange as the reservoir pressure declines.



30/48

Fetkovichs Method: Comparisonbetween Current and Future IPRs



31/48

Fetkovichs Method: 3rd CaseCase 3: pr > pb and pwf < pb

o and Bo are evaluated at the bubble-pointpressure pb.



32/48


33/48

Advantages of Horizontal Oil WellSince 1980, horizontal wells began capturing an

ever-increasing share of hydrocarbon production.

Horizontal wells offer the following advantages

over those of vertical wells:Large volume of the reservoir can be drained by each

horizontal well.

Higher productions from thin pay zones.



34/48

Advantagesof Horizontal Oil Well Cont.)Horizontal wells minimize water and gas zoning

problems.

In high permeability reservoirs, where near-wellbore gasvelocities are high in vertical wells, horizontal wells can

be used to reduce near-wellbore velocities andturbulence.

In secondary and enhanced oil recovery applications,long horizontal injection wells provide higher injectivityrates.

The length of the horizontal well can provide contactwith multiple fractures and greatly improve productivity.



35/48

Horizontal Oil Well vs. Vertical Oil WellThe actual production mechanism and reservoir

flow regimes around the horizontal well areconsidered more complicated than those for thevertical well, especially if the horizontal section of

the well is of a considerable length.Some combination of both linear and radial flow actually

exists, and the well may behave in a manner similar tothat of a well that has been extensively fractured.



36/48

IPRs for Horizontal WellsSeveral authors reported that the shape of

measured IPRs for horizontal wells is similar tothose predicted by the Vogel or Fetkovich methods.

The authors pointed out that the productivity gain from

drilling 1,500-foot (460m) long horizontal wells is two tofour times that of vertical wells.



37/48

Horizontal Well IllustrationFigure shows the

drainage area of ahorizontal well of length Lin a reservoir with a pay

zone thickness of h.Each end of the

horizontal well woulddrain a half-circular area

of radius b, with arectangular drainageshape of the horizontalwell.



38/48

Horizontal Well Drainage AreaA horizontal well can be looked upon as a number

of vertical wells drilling next to each other andcompleted in a limited pay zone thickness.

Assuming that each end of the horizontal well is

represented by a vertical well that drains an area ofa half circle with a radius of b, Joshi (1991)proposed the following two methods for calculatingthe drainage area of a horizontal well.

Joshi noted that the two methods give differentvalues for the drainage area A and suggestedassigning the average value for the drainage of thehorizontal well.



39/48

Joshi Method IJoshi proposed that the drainage area is

represented by two half circles of radius b(equivalent to a radius of a vertical well rev) at eachend and a rectangle, of dimensions L(2b), in the

center.The drainage area of the horizontal well is given then by:

Where

A = drainage area, acres

L = length of the horizontal well, ft

b = half minor axis of an ellipse, ft



40/48

Joshi Method IIJoshi assumed that the horizontal well drainage area is

an ellipse and given by:

Where a is the half major axis of an ellipse.

Most of the production rate equations require thevalue of the drainage radius of the horizontal well,which is given by:

Wherereh = drainage radius of the horizontal well, ftA = drainage area of the horizontal well, acres



41/48


42/48

IPR Calculations for Horizontal WellsFrom a practical standpoint, inflow performance

calculations for horizontal wells are presented hereunder the following two flowing conditions:

Steady-state single-phase flow

Pseudosteady-state two-phase flow



43/48

Horizontal Well Productivityunder SS FlowThe steady-state analytical solution is the simplest

solution to various horizontal well problems.

The steady-state solution requires that thepressure at any point in the reservoir does not

change with time.The flow rate equation in a steady-state condition

is represented by:

WhereQoh = horizontal well flow rate, STB/day

p = pressure drop from the drainage boundary to wellbore, psi

Jh = productivity index of the horizontal well, STB/day/psi



44/48

Productivity Indexof the Horizontal WellThe productivity index of the horizontal well Jh can

be always obtained by dividing the flow rate Qoh bythe pressure drop p, or:

Several methods are designed to predict theproductivity index from the fluid and reservoirproperties. Some of these methods include:Borisovs Method

The Giger-Reiss-Jourdan MethodJoshis Method

The Renard-Dupuy Method



45/48

Horizontal Well Productivityunder PSS RegimeThe complex flow regime existing around a

horizontal wellbore probably precludes using amethod as simple as that of Vogel to construct theIPR of a horizontal well in solution gas drive

reservoirs.If at least two stabilized flow tests are available,

however, the parameters J and n in the Fetkovichequation could be determined and used toconstruct the IPR of the horizontal well.In this case, the values of J and n would not only account

for effects of turbulence and gas saturation around thewellbore, but also for the effects of nonradial flowregime existing in the reservoir.



46/48

1. Ahmed, T. (2006). Reservoir engineering

handbook (Gulf Professional Publishing). Ch7


47/48

1. Vertical Gas Well Performance

2. Pressure Application Regions

3. Turbulent Flow in Gas Wells

A. Simplified Treatment Approach

B. Laminar-Inertial-Turbulent (LIT) Approach (Cases A.

& B.)


48/48

Documents

IPR Methods