Risking of Prospects and Segments

7/23/2019 Risking of Prospects and Segments

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Risking of prospects andsegments


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Probability concept Fundamental rules

Probability = 1- RiskP=1.0 means 100% certainty

P=0.0 means 0% certainty

1.0 0.0

0.9 0.1

0.8 0.2

0.7 0.3

0.6 0.4

0.5 0.5

0.4 0.5

0.3 0.7

0.2 0.8

0.1 0.9

0.0 1.0

RISK

PROBABILITY


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Probability concept Multiplication rule.

P=Pa x Pb x Pc x Pd.

Used when estimating theprobability of discovery formapped prospect.

Prospect probability is a product ofseveral independent factors (suchas reservoir, trap, charge and

retention).


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Probability concept Addition rule.

P=Pa + Pb.

Deal with several outcomes such as

the question of whether oil or gaswill be the dominant phase in theprospect being evaluated.


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Probability concept Combination rule.

(1-P)=(1-Pa) x (1-Pb).

Deals with interdependency betweenprospects.


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Risk model Estimate the probability of making

a discoveryMake the volume estimates less

wrong (White, 1993)

Establish risking guidelines prior toassessment

To provide consistency

Attempts to promote objectivity


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Risk levels

Split into prospect level and playlevel. Play attributes assumed to be common to

all prospects in the play are grouped in theplay level.

Prospect risk factors are assumed to beunique for each prospect and estimates

vary from prospect to prospect.


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Play and Prospect risk

Retention after accumulation

Migration into the structure

Presence of effective sealTiming of structuring

Presence of structurePresence of mature source rock

Prospect risk factorsPlay risk factors

Presence of effective porosityPresence of reservoir facies

Risk Model


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Probability of discovery The estimated prospect probability

is not the probability of making adiscovery but:

The probability of finding at leastthe minimum quantity of HC

estimated in our resourceassessment.

CCOP-REP Vung Tau 1996


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Probability of discovery The product of major probability

factors Pdisc = Pplay x Pprospectwhere Pplay = Preservoir facies x Pmature source x Ptiming

and Pprospect= Pporosity x Pgeometry x Pseal x Pmigration x

Pretention.

Probability factors are evaluated withrespect to presence andeffectiveness.


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Probability of regionallydistributed reservoir facies

0.0 - 0.2Reservoir unit not present in the play area

0.2 - 0.4Presence is based on analog model

0.4 - 0.6Regional distribution of the unit is probable

0.6 - 0.8Found in at least one well; convincing seismic dataclearly indicate a regional distribution of the unit

0.8 -1.0Found in all wells in the play area; facies modeling andseismic data clearly indicates presence of the reservoir

unit in between wells

Quantitativeprobabilityrange

Technical tests criteria

Describes the probability that a regionally

distributed facies that constitute the reservoirinterval in the mapped prospects andunmapped resources exist.


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Probability of sufficientmature source rock

0.0 - 0.2Presence of mature source rock is probable

0.2 - 0.4Presence is based on analog model

0.4 - 0.6Wells in play have HC shows/well samples show presenceof source rock & geochemical modeling predicts maturesource rock

0.6 - 0.8Found in at least one well; convincing seismic data clearly

indicate a regional distribution of the unit

0.8 -1.0Commercial production in play area, wells tested moveableHC

Quantitativeprobability

range


Describes the probability that a sufficientmature source rock exists.


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Source rock evaluation

Best done through basin modeling

Factors to be examined

Quality of potential source rock

Type of hydrocarbon generated

Areal and spatial distribution of mature

source rock within play area Poin in time for onset and end of oil

generation

Volume of hydrocarbon generated


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Probability of timing ofstructuring

Describes the probability that thestructures have been present before theend of the hydrocarbon generation.

0.0 - 0.2Unambiguous data suggest that the trap was not inexistecen priori to the end of HC generation.

0.2 - 0.4Unconvincing data indicate that the trap was not present

prior to the end of the HC generation

0.4 - 0.6Based on the available data, it is equally probable that thetrap was in existence prior to the end of the HCgeneration.

0.6 - 0.8Convincing data indicate trap existed before migration

0.8 -1.0Unambiguous data suggest trap existed before start ofmigration

Quantitative

probabilityrange



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Probability of the effective

porosity

0.0 - 0.2Reservoir rock has parameters lower than the minimum0.2 - 0.4Adequate reservoir parameters may exist in trend

0.4 - 0.6Existence of effective reservoir parameters is equallyprobable

0.6 - 0.8Lateral continuity is probable as indicated by seismic, well,and/or outcrop data

0.8 -1.0Identical reservoir rock parameters are found in field ordiscovery in immediate vicinity



Describes the probability of the existence of

an effective reservoir facies with reservoirparameters equal to or higher than the

minimum estimate


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Probability of

structure/geometric body

0.0 - 0.2Identical structure proven absent

0.2 - 0.4Structure poorly defined by seismic

0.4 - 0.6A firm conclusion cannot be drawn

0.6 - 0.8Convincing data indicates probable structure

0.8 -1.0Identical structure in immediate vicinity tested

successfully



Describes the existence of the mapped

structural/geometrical body with a bulk rockvolume equal or larger than the minimum

value used in the analysis.


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Probability of effective seal

0.0 - 0.2Sealing mechanism proven unsuccessful

0.2 - 0.4Sealing mechanism poorly defined

0.4 - 0.6Presence of seal is equally probable

0.6 - 0.8Same sealing rock unit tested in trend

0.8 -1.0Presence of thick, regionally extensive and effective sealing



Describes the probability of an efficient

top, base and lateral seal of thestructure.


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Probability of migration

0.0 - 0.2Trap is not within a migration pathway

0.2 - 0.4Migration path is complicated and tortuous

0.4 - 0.6Available data indicate that it is equally probable that HChave migrated into the trap

0.6 - 0.8Trap is situated within a migration pathway

0.8 -1.0Unambiguous data verify that HC migrated into similar traps



Describes the probability of efficient

migration of hydrocarbons from thesource to the mapped structure.


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Probability of retention after

accumulation Evaluates reactivation of faults,

regional uplift and tilting afteraccumulation

0.0 - 0.2Trap has experienced disturbances by tectonic movements

0.2 - 0.4Sealing mechanism after accumulation is poorly defined

0.4 - 0.6Equally probable that the trap has been or has not beenaffected by tectonic movements after accumulation

0.6 - 0.8Overlying sediments were eroded after accumulation

0.8 -1.0No indication of tectonic movement after accumulation




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Definition of terms Marginal probability

The chance that at least one field of at leastminimum size exists in the play. This chancereflects the regional, play-specific riskswithin the play

Conditional probability

The chance that the prospect would hold a

field of at least the minimum size oncondition that the play were regionallysuccessful

(D.A. White, 1993)


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Play probability Confirmed play

Probability (P) is 1 Tested and flowed HC to the surface

(technical discovery) Example:

1.0Marginal play probability

1.0Timing of structuring

1.0Presence of reservoir facies

1.0Presence of mature source rock

Probability (Play)Play risk factors

Marginal play probability = 1.0 x 1.0 x 1.0


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Play probability Unconfirmed play

Probability is between 0 and 1Play is not drilled yet or play has no

technical discovery Example:

0.9Marginal play probability

1.0Timing of structuring

1.0Presence of reservoir facies

0.9Presence of mature source rock

Probability (Play)Play risk factors

Marginal play probability = 1.0 x 0.9 x 1.0


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Prospect probability

Conditional probability The chance that the prospect will be an

accumulation on the condition that the play isfavorable to hydrocarbon accumulation (GeoX)

0.512Conditional prospect probability

1.0Retention after accumulation0.8Migration into the structure

1.0Presence of effective seal

0.8Presence of effective porosity

0.8Presence of structure

Probability (Prospect|Play)Prospect risk factors

Conditional prospect probability = 0.8 x 0.8 x 1.0 x 0.8 x 1.0


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Unconditional probability Probability of success = Pplay * Pprospect

0.54Dry hole risk

0.46Unconditionalprobability

0.9Marginal playprobability

0.512Conditional prospect

probability

ProbabilityPROSPECT WHOSE PLAYIS NOT CONFIRMED

0.488Dry hole risk

0.512Unconditionalprobability

1.0Marginal playprobability

0.512Conditional prospectprobability

ProbabilityPROSPECT WHOSE PLAYIS CONFIRMED

Unconditional probability = 0.9 x 0.512Unconditional probability = 1.0 x 0.512

Dry hole risk = 1 0.512 Dry hole risk = 1 0.46


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Risk dependency -a probability perspective

Would your estimate ofA2 COS change if youknew the outcome ofdrilling the A1 segment?

If YES, then you implythat there is risk

dependency between A1

A1

A230% COS

20% COSand A2.

Copyright 2004 GeoKnowledge

Shared risk approach to


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Shared risk approach to

modeling risk dependency Consider the segments A1 and A2. Theshared risk approach partitions the chanceof adequacy into ...

P(shared), that captures all chance ofadequacy that is shared between A1 and A2,and ...

Independent conditional probability for A1and A2, given that the shared probability isOK; P(A1|shared) and P(A2 |shared).

Thus ...

P(A1) = P(A1| shared) * P(shared) = 0.3

P(A2) = P(A2| shared) * P(shared) = 0.2

A1

A230%

COS20%COS


Geological interpretation of risk


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g pdependency

FULL dependency example, proven play

Geologic Setting:

Deepwater fan in a proven play.

There is a 30% chance that the

reservoir was deposited at A.

If the reservoir is proven at A, then

the chance at B will improve to 67%.

The reservoir cannot be deposited at B

without also being deposited at A.

A B

.30 .20

.10

.70 .50

alDecreasing

Reservoir COADistalProxim

What is probability that sand reached A? 30%

What is the probability that sand reached B, given thatit reached A? .2/.3 = 67%

Shared Shared Probability Independent ProbabilityShared x Independent

Segment Risk P(shared) P(segment | shared)P(segment)

A 1.00.30B .67.20

1 - .70 = .30.70


G l i l i t t ti f i k


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Geological interpretation of risk

dependencyPARTIAL dependency example, proven play

What is probability that the system was deposited? 50% (must be riskedseparately)

Given that it was deposited, what is the chance that it is present in A?

.3/.5 = 60% Given that it was deposited, what is the chance that it is present in B?

.2/.5 = 40%

Geologic Setting:

Channel system in a proven play.

There is a 50% chance that the channel was

deposited in this area.

It is more likely to be at A (Channel axis) than

at B (channel margin).

Due to the sinuosity of the channel, it could

have been deposited at B without being

deposited at A. Or it could have been

deposited in the area, but at neither A nor B.

*Total reservoir COA

Chance the channel was deposited = 50%

B

A.20*.30* Axis

Margin

Shared Shared Probability Independent ProbabilityShared x Independent

Segment Risk P(shared) P(segment | shared)P(segment)

A .60.30B .40.20

1 - .50 = .50.50



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Shared risks in GeoX 5.4 Set at the level of individual risk factors by

enrolling segments in risk dependency groups

System constrains value of shared probabilityaccording to chance of adequacy probabilities

for segments in risk dependency group

GeoX options for defining shared risksbetween segments

Shared Probability

Max Correlation

Play chance

Note: Technically speaking, these are all variationsof the same method.



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Organization and Flow

Risking of Prospects and Segments

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