Prospect Risk & Volume Assessment

Trainer(s): Jan de Jager
Duration: 5 sessions of 3 hours per day

Business context

A decision to drill an exploration well with the objective to find a new oil or gas field must be based on a sound assessment of the prospect risk and of the volumes: what is the chance that a well will find hydrocarbons, and how much could it be? Risk and volume assessments form the basis for decisions to drill a well or not, and as such form the link between subsurface evaluation and the business aspects of the petroleum industry.  This course explains how risks and volumes can be assessed in a realistic manner, based on a sound understanding of the geological details of the prospect as well as of its regional geological setting and current play understanding.

Who should attend

This course is designed in the first place for geoscientists working in exploration, for prospect portfolio analysts and for their direct supervisors. It is also a very instructive course for staff from disciplines working closely with exploration staff, such as reservoir engineers, petrophysicists and geophysicists.

Course content

The course will demonstrate that realistic risk and volume assessment is not a "black box" operation, but needs geological understanding of the prospect, and the regional setting.

Specific topics that will be discussed include:

  • The fundamentals of Risk and Volumes assessment; translating geological understanding into reasonable numbers and ranges.
  • The difference between risk and uncertainty.
  • Fundamentals of statistics; including explanation of distribution curves, understanding of expectation curves, do's and don'ts for adding risked volumes, and Bayes theorem.
  • Uncertainty of trap, reservoir, seal and charge, illustrated by examples.
  • Guidelines and exercises for estimating risks realistically and consistently.
  • Calculating volume ranges for prospects and for portfolios of prospects; how to add prospect volumes for a correct representation of prospect portfolios.
  • Incorporation of geophysical evidence (DHIs) in a realistic risk assessment. 

Learning, methods and tools

The VILT will be delivered online in5 sessions of 3 hours per day, with 2 breaks of 10 minutes per day. It is the intention to have at least 2 smaller exercises per day. Time will be reserved for recapitulation, questions and discussions. 

VILT will be conducted either via Zoom or Microsoft Teams. Presenting materials can easily be done on this platform. When participants need to ask a question, they can raise their hand, write notes or interrupt the Instructor by using their microphone. The presenter can switch to a screen where he/she can see all participants (also when each participant is sitting in another location e.g. at home). 

Each topic is introduced by a lecture, and learning is re-enforced by practical exercises and discussions. Hand-out material in paper and/or electronic format will be provided.

Day by day programme

DAY 1: Risks, Volumes and Uncertainty 

Introduction participants and course instructor 


An outline of the programme and the objective of the course.

Introduction to Risk & Volume assessment: the main concepts and discussion of how the results of risk & volume assessments are used in the business

  • Exercise: are we good estimators

Risks, Volumes and Uncertainty

The difference between risk and uncertainty, basics of essential statistical concepts, the play elements and workflow to assess prospect risks, biases in estimating uncertainties, the results of probabilistic volume assessments and their representation in expectation curves and frequency plots, exercises to enhance understanding of introduced concepts

  • Exercise: making an expectation curve and a probability density function

Prospects and Plays

Demonstration of how understanding of the regional geology, petroleum systems and hydrocarbon plays is an essential element in the assessment of risks & volumes for individual prospects; exercise on the use of play maps as aid in risk assessment

  • Exercise: prospect ranking based on a play map

DAY 2: The Risk Elements: Traps and Reservoirs 

Summary of Day 1

Re-cap of main learning points 


Risks and uncertainties associated with hydrocarbon traps, the difference between spill and leak points, how to deal with sealing faults and overpressures, what are the risks of stratigraphic traps, how to estimate realistic uncertainty ranges for hydrocarbon column length, exercises

  • Exercise: determining spill- and leak-points


Risks and uncertainties associated with reservoir rocks, how to deal with layered reservoirs, waste zones and irregularly shaped reservoirs, facies and depth trends in reservoir characteristics, exercises

  • Exercise: determining uncertainty distribution for porosity

DAY 3: The Risk Elements: Seals and Charge 

Summary of Day 2

Re-cap of main learning points 


Mechanisms of seal failure, how to deal with leaky seals and differential leakage of gas, overpressures and impact on seal risk and column length prediction, exercises to enhance understanding

  • Exercise: calculating shale gouge ratio


Impact of source rock types and timing issues for charge assessment, how to deal with mixed columns (oil and gas), formation volume factors (gas expansion and oil shrinkage), hydrocarbon saturations and recovery factors, the impact of long transition zones in tight reservoir rocks

  • Exercise: HC fill based on pressure information 

DAY 4: Risk and Volume assessment in practice 

Summary of Day 3

Re-cap of main learning points 

Risk assessment

Practical exercise in small break-out groups on prospect risk assessment, group discussion on the impact of positive and/or negative geological indications for the presence or absence of play elements

Exercise and discussion: Determining the Chance Factors for a prospect 

Volume assessment

Practical back-of-the-envelope volume calculation exercise, how to quickly calculate low, medium and high volumes for a prospect, recapitulation of how to select appropriate distributions

  • Exercise: Calculating low mid and high prospect volumes - back-of-the-envelope 

DAY 5: Bringing it all together 

Summary of Day 4

Re-cap of main learning points 

Volumes and portfolios

The impact of dependencies between prospects in a portfolio, risking and volume assessment of prospects with stacked reservoir-seal pairs, adding probabilistic prospect volumes statistically correct

Exercise: determining dependency between prospects 

Geophysical evidence

The impact on prospect POS (probability of success) of direct hydrocarbon indicators (DHIs) and/or positive (or negative) evidence form controlled source electromagnetics (CSEM) - consistent with Bayes' theorem

Exercise: Calculating an updated POS based on geophysical evidence 

Look-back studies

The only way to improve prospect predictions is by comparing our past predictions with actual well results. It will be shown how we can we best do this, and common industry trends will be discussed. 

Course Close-out