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1SINTEF Petroleum Research
Recent advances in petroleum assessment,Trondheim 19 20 October 2005
Risk assessment.
Principles and experiencesKjell ygard
SINTEF Petroleum Research
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2SINTEF Petroleum Research
Risk assessment
The purpose of risk assessment in petroleum explorationis to estimate the probability of discovery prior to drilling
of a mapped prospect.
Play level evaluationCalculation of the economic value of prospectsAssessment of the undiscovered resources in a given area duringplay evaluation.
Ranking of prospects
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3SINTEF Petroleum Research
Risk assessment
High degree of uncertainty in exploration for oil and gas
Half of drilled exploration wells are dry
About 50% of the discoveries are non profitable
Geologists perform risk assessment in a subjective
manner
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4SINTEF Petroleum Research
Geological risk assessment
The Geological risk assessment requires an evaluation ofthose geological factors that are critical to the discovery of
recoverable quantities of hydrocarbons.The probability of discovery is defined as the product of thefollowing major probability factors, each of which must be
evaluated with respect to presence and effectiveness:Probability of:
Reservoir
Trap Hydrocarbon charge
Retention of hydrocarbons after accumulation
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The Probability Consept
1. Pprob. = 1 Prisk
2. The probability of the simultaneousoccurrence of several independent events isequal to the product of their individualprobabilities. P = Presx Ptrapx PHCx Pret
3. Given the occurrence of several mutuallyexclusive events, P = Pa+ Pb
4. The probability of either one or both of twoindependent events can be estimated bycalculating the risk that neither of the eventswill occur. (1-P) = (1 - Pa) x (1 Pb)
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Oil Prospect Reserve
Monte Carlo Calculation
1 ITERATION
Transform
ation
Access
Sou
rceArea
Conver
tibility
SealEfficiency
Gas/O
ilRa
tio
RecoveryF
ac
tor
Volum
eGasC
ap
OilSaturation
Porosity
NetTrapVolum
e
Minimum
Most Likely
Maximum
Phase
Form
atio
n
Volum
e
Factor
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Risk vs. Uncertainty
Risk is the probability that the parameter of interest
fails to work at the minimum level expected
Uncertainty is the variation in or the range of
possible outcomes
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Prospect Probabilities
The probability of discovery is a value that is based partlyon objective knowledge and historical data, partly on
extrapolations and partly on our subjective judgements oflocal geological parameters.
Post-drill evaluation
Reliability of the database
Relevant geological models
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Reservoir
Probability of existence of reservoir facies with minimumnet thickness and net/gross-ratio
Probability of effectiveness of the reservoir, with respect tominimum porosity, permeability and hydrocarbonsaturation
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Reservoir probability guidelines
Presence of effective reservoir facies
Porosity evaluation
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Trap mechanism
Probability of presence of the mapped structure with aminimum rock volume as prognosed in the volume
calculation. Geometrical body.
Probability of effective seal mechanism for the mappedstructure.
T m h i m b bilit g id li
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Trap mechanism probability guidelines
Structural/stratigraphic complexityregarding rock volume Effective seal mechnism
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Petroleum Charge
Probability of effective source rock in terms of theexistence of sufficient volume of mature source rock of
adequate quality located in the drainage area of themapped structure.
Probability of effective migration of hydrocarbons from the
source rock to the mapped structure at the right time.
Petroleum Charge= Effective drainage area X Thickness
map X TOC and HI X Transformation X Expulsion XSecondary migration
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15SINTEF Petroleum Research
Retention after accumulation
The probability of effective retention of petroleum in the prospect afteraccumulation
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16SINTEF Petroleum Research
Hydrocarbons indicators
Oil seepage, pockmarks at sea-bottom, gas anomalies inseismic data etc., are all indicators of hydrocarbons being
present.
A direct hydrocarbon indicator (DHI) is defined as a
change in seismic reflection character (seismic anomaly)which is the direct result of the reservoirs fluid contentchanging from water to hydrocarbons.
Real or false:- Opal A/CT and Opal CT/Quartz
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17SINTEF Petroleum Research
Direct Hydrocarbon Indicator
Rock PropertiesShould See Should not See
Do See
Do not See
DHI- Attribute
Poor rockproperties model
Seismic artifact
No prospect
Poor seismicquality
Relay on
geologicmodells andPetroleum
System
Seismic
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18SINTEF Petroleum Research
Risk assessment
Predicted
Not predicted
Not predicted Predicted
Ge
ophysica
ldriven
Geological driven
Reservoir presence
Reservoir deliverability
Seal presence
Seal capasity
Source presence
Access to charge
Retention afteraccumlation
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19SINTEF Petroleum Research
Petroleum Risk Assessment litterature
http://www.ccop.or.th/projects/RiskAssess.pdf
Rose, P R, 1987. Dealing with risk and uncertainty in exploration: how can weimprove? AAPG Bulletin, v. 77, no 3, p 319-326
Rose, P R, 1992. Chance of success and its use in petroleum exploration, in RSteinmetz, ed., The business of petroleum exploration: AAPG Treatise ofPetroleum Geology, Handbook of Petroleum Geology, p 71- 86
White, D A, 1993. Geologic risking guide for prospects and plays: AAPG Bulletin, v
77, p 2048-2061Otis, R and Schneidermann N, 1997. A process for evaluating exploration prospects.AAPG Bulletin, v 81, no 7, p 1087-1109.
Ulmishek, Gregory F., 1986: Stratigraphic aspects of petroleum resourceassessment, in Rice, D.D., ed., Oil and gas assessments Methods andapplications: AAPG Studies in Geology #21, p. 59-68.
Milton, N. J., and Bertram, G. T., 1992. Trap Styles-A New Classification Based onSealing Surfaces. AAPG Bulletin, v 76, no. 7, p 983-999.