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