FORMATION EVALUATION

PETE 663

Summer 2010

NET SAND/PAY, RESOURCES, AND RESERVES

Notes by J. Jensen, W. Ayers, D. Schechter

DEFINING NET PAY

• What is “net pay”?• Several definitions; sometimes confusing• How we determine reserves depends on

objectives and data available– Static: resource and reserve calculations; what is there and

estimated recoverable?– Dynamic: what will flow?

• Data used– Logs– Core– Well tests– Production– Seismic

NET SAND / PAY, RESOURCE AND RESERVE DETERMINATIONS

Methods• Volumetric (Static)

• Dynamic

• Production History

• Analogy

• Static DefinitionOOIP = 7758 Ah φ(1 - Sw)/Boi

• Assumes net properties• Evaluating net

– Identify any area without HC’s– Logs: apply series of criteria

• (Sw > cutoff) AND (Vsh > cutoff) AND (φ < cutoff) etc…• Compare with core, if available• Calibrate to seismic?

DETERMINING HYDROCARBONSIN-PLACE

Fluid Distribution

INPUTS TO VOLUMETRIC RESERVESGRC

0 150

SPCMV-160 40

ACAL6 16

ILDC0.2 200

SNC0.2 200

MLLCF0.2 200

RHOC1.95 2.95

CNLLC0.45 -0.15

DTus/f150 50

001) BONANZA 1

10700

10800

10900

h

Calculate φ, Sw

Modfoed from NExT, 1999

• Vshale• Thickness• Porosity

NET OIL PAY ISOPACH MAP

0

Well #245’

Well #121’

Well #564’

Well #355’

Well #449’

Dry Hole #10’

Dry Hole #22’

20

40

50

60

NExT, 1999

SOME TERMINOLOGY

MORE TERMINOLOGY

Also, calledTrue StratigraphicThickness (TST)

Measured Thickness (MT)

CORRELATIONTECHNIQUES

DATUM

Log patterns

Marker beds

WELL-LOG CORRELATION

Stratigraphic Cross Section

STRUCTURAL CROSS SECTION

B Marker

DATUM

RESERVOIR DETERMINATION

DEFINING NET PAY

Common alternatives for net pay definition– Use static criteria

• (Sw > cutoff) AND (Vsh > cutoff) AND (φ < cutoff) etc…

– Try to correlate k with log measurements

• Use core data

0.01

0.1

1

10

100

0 5 10 15 20

Perm

eabi

lity,

mD

Porosity, %

DEFINING NET PAYCore data & logs for net pay determination– Define k cutoff e.g., 1mD

0.01

0.1

1

10

100

0 5 10 15 20

Perm

eabi

lity,

mD

Porosity, %

– Define φ value e.g. φ = 10%– Apply net pay using log φ

value φ > 10%– Note errors arise

• k > 1 AND φ < 10%– 11 of 86– Prob(k > 1 AND φ < 10) = 13%

• k < 1 AND φ > 10%– 2 of 86– Prob(k < 1 AND φ > 10) = 2%

• Prob(k > 1 | φ < 10%) = 24%

DEFINING NET PAY

Deciding on predictor log(s)– What controls perm?– Carbonates

• Grain size and sorting less effect

• Diagenesis more important• Critical thresholds often seen

– Below φ = 10, k variable– Above φ = 10, k systematic

0.01

0.1

1

10

100

0 5 10 15 20

Perm

eabi

lity,

mD

Porosity, %

RESERVOIR DETERMINATION

Net-to-Gross Determination

Defining Gross Thickness, Net Sand,and Net Pay

Measure thickness (MT) of Well 1 < MT of Well 2

(Transitional)

Net Pay Map DeterminationA)

B)

C)

Combination Trap:Faulted Anticline andStratigraphic Pinch-Out

Structure Map and Cross Section

Summary

• OOIP = 7758 Ah φ(1 - Sw)/Boi

• Oil reserves = OOIP x R.F.

• OGIP = 43,560 Ah φ(1 - Sw)/Bgi

• Gas reserves = OGIP x R.F.

• Remaining reserves = Reserves at original conditions - cumulative production

Modfoed from NExT, 1999