Doing Yet-To-Find Resources YTF with GeoX 5.8 JUL… · GeoX is a collection of assessment tools designed to support and promote high quality exploration decisions. It focuses the

GeoX Play Assessment Primer DRAFT

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Copyright © 2009 GeoKnowledge

DRAFT/3JULY09 STD GeoX 5.8

Doing Yet-To-Find Resources A GeoX Play Assessment Primer


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Thunes vei 2 • 0274 OSLO, Norway

Tel: +47-22941120 • Fax: +47-22941121

A Primer on Play Assessment with GeoX Copyright © 1992 - 2009 GeoKnowledge AS

All Rights Reserved.

No part of this software or documentation may be copied, photocopied,

reproduced, translated, or reduced to any electronic medium or machine-

readable form without prior written consent from GeoKnowledge AS.

The information in this document is subject to change without notice and

should therefore not be construed as a commitment by GeoKnowledge AS.

GeoKnowledge AS assumes no responsibility for any consequences

resulting from errors that may appear in this document.

The software described in this document is furnished under license and

may be used or copied only in accordance with the terms of such license.

Oslo, July 2009


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Table of Contents

INTRODUCTION .................................................................................. 1

OVERVIEW OF GEOX ........................................................................ 2

LOGGING ON TO GEOX .................................................................... 4

THE GEOXPLORER ............................................................................ 5

THE BASIC PLAY ASSESSMENT WORKFLOW ............................ 7

THE RIFT MARGIN CARBONATE PLAY ........................................ 9

CREATING A PLAY AND A PLAY ANALYSIS ...............................10

THE PLAY ANALYSIS NOTEBOOK ................................................12

DOCUMENTING A PLAY ANALYSIS ..............................................15

THE PLAY ANALYSIS SET-UP .........................................................17

SAVING THE PLAY ANALYSIS .......................................................18

OVERALL PARAMETERS ................................................................20

SHARED PLAY RISKS .......................................................................21

DEFINING THE POSTULATED FEATURES ...................................22

POSTULATED SETUP ........................................................................24

POSTULATED VOLUME INPUTS ....................................................25

CONDITIONAL RISKS .......................................................................27

CALCULATING YTF RESOURCES .................................................28

REVIEWING AND INTERPRETING RESULTS ..............................29

YET-TO-FIND RECOVERABLE RESOURCES.............................................30

ABOVE SCREENING THRESHOLD YTF ...................................................33

SIZE-BY-RANK TABLE AND DIAGRAM ....................................................34

PERCENT YTF VOLUME-BY-SIZE DIAGRAM ...........................................35

APPENDIX A: PLAY ANAYSIS INPUTS ..........................................37

ABOUT SETUP ANALYSIS ......................................................................38

ABOUT DEFINITION: ENROLMENT .........................................................40

ABOUT DEFINITION: DISCOVERY HISTORY CHART ................................42

ABOUT THE OVERALL PARAMETERS .....................................................43

ABOUT CORRELATION (OVERALL) ........................................................45

ABOUT SETUP HC FLUIDS MODELLING (POSTULATED) ...........................47

ABOUT THE VOLUME SETUP (POSTULATED) ..........................................48

ABOUT VOLUME WITH AREA, THICKNESS & GF (POSTULATED) ............50

ABOUT VOLUME W. AREA-THICKNESS_IN_TABLE (POSTULATED)..........52

ABOUT THE FLUIDS SETUP (POSTULATED) ............................................54

ABOUT FLUIDS PARAMETERS USING DIRECT ENTRY (POSTULATED) .......55

ABOUT FLUIDS PARAMETERS USING EQUATIONS (POSTULATED .............57

APPENDIX B: GLOSSARY ................................................................59


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1


Introduction This is a short Primer

1 on doing the play assessment with GeoX. It

focuses the basics of doing assessment of single (part) plays and

complements the GeoX Primer on assessment of segment risks and

resources.

The rest of the Primer is organized as follows. The next section provides a

short overview of GeoX with the key elements that support your risk and

resource assessment workflow. The following sections take you through

the basics of getting started with GeoX in terms of what we call the

housekeeping tasks of creating a play folder, creating a play analysis and

documenting the assumptions and context of the analysis. Thereafter we

go through the basics of entering the necessary input parameter estimates

for doing an assessment of the Yet-To-Find potential in a part play with

postulated features. We review in detail the main input context, the overall

play parameters, the field size distribution, the fluid, and the risk input

estimates. The last sections review the results.

Appendix A reviews in more detail the main input of the GeoX play

analysis tool.

The Primer complements the one-day course on "Doing Play Fairway

Assessment with GeoX". It is meant to be a reference that you can consult

after the course. However, it alternatively can also provide an introduction

to doing assessments with GeoX for someone that has not taken the

course.

1 prim·er1 [ pr m r ] n.

1. A book that covers the basic elements of a subject.


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Overview of GeoX GeoX is a collection of assessment tools designed to support and promote

high quality exploration decisions. It focuses the critical integrative,

judgement-intensive exploration decisions that rely on the assessment of

resources, risks and full cycle economics. It provides a complete

framework for consistent, best practice evaluation of exploration

opportunities.

The GeoX workbench has 3 main tools: gPlayR for the play-level

evaluation of Yet-To-Find resources, gSegmentR for the evaluation of

risks and resources at the level of single container exploration targets, and

gFullCycle for the evaluation of after-tax economics of exploration

ventures. Additional tools are available for aggregating analyses,

classifying resources and assessing exploration portfolios. The gPlaySum

tool for the analysis of risks and resources in a play fairway that consists of

multiple part plays complements the gPlayR tool.

GeoX has a relational database that supports industry-standard database

systems such as Oracle or SQL Server. The database is used to store,

access and link analyses organized in a basin-play-segment framework.

The database supports integrative application of the family of tools. The

database also facilitates sharing and exchanging data with colleagues,

other applications and other systems.

Analyses are the primary work unit. There is a different type of analysis

for each GeoX tool. Tools are launched according to the type of analysis

that is accessed in the GeoX database. For example, gPlayR is launched

when you access (or create a new) a play analysis. Analyses are viewed,

edited and estimated in a notebook-format interface with a uniform and

consistent syntax across all GeoX tools.

In this primer we will refer to the GeoX tools by referencing the type of

analysis that is associated with the tool. In other words, when we refer to a

play analysis, we either are referring to the analysis of specific play or the

gPlayR tool in general.

By enabling you to maintain multiple analyses of an exploration target, the

system supports a process where you can consider systematically

alternative hypotheses and scenarios. Analyses are Test, Approved or

Historical, where both the Approved and all Historical analyses are read-

only from the database. This status categorization and administration


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enables you to maintain a systematic record of how ideas, data and

understanding evolve through the exploration life cycle.

The focus of this Primer is the gPlayR tool for analysis of the YTF potential

of a play. However, all GeoX tools share a common notebook format with

the same set of functions for accessing, editing, calculating, storing,

printing and exchanging analyses. Once you master the mechanics of

using gPlayR you are also well positioned to do the other tools in the

workbench.

The segment is the basic assessment building block in GeoX. It is the

smallest definable assessment unit2. Examples of segments include

individual reservoir units and fault compartments. A segment must be

within a single play or sub-play

A play is a family of postulated potential accumulations, mapped potential

accumulations, assessed potential accumulations & discoveries that have

the same geological controls on gross reservoir, hydrocarbon source & top

seal. The play (part-play) is the basic assessment unit (BAU) in play

assessment with GeoX.

A prospect is a collection of segments. It can for example be a series of

stacked reservoirs, or a group of fault compartments, or combinations of

reservoir units and fault blocks. A prospect can span multiple plays as it

can contain segments that are located in different plays.

Consider the Alpha prospect (schematic cross-section below). Alpha

includes 4 segments (A, B, C and D). There are three reservoir units (C, D

and A-B) where unconformity separates the C and D units from the A-B

unit. The two segments (C&D) above the non-conformity are in the “U”

(upper) play while the A and B segments below the non-conformity are in

the “L” (lower) play. The A and B fault compartments are in the same

reservoir unit. Alpha spans two plays: Play U and Play L.

2 As we will see, one might also consider the play analysis as a separate assessment unit.

However, plays are assessed as composed of postulated potential accumulations that can

be viewed as segments. In GeoX 5.8.0 the postulated potential accumulation is defined

separately from the play analysis and the smallest assessment unit is then clearly the

segment.


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Logging on to GeoX GeoX is typically installed as a Citrix-application. This means that you

access GeoX via Citrix.

Once you have accessed GeoX, the system will first open the GeoX splash

screen and then immediately after that it will display the GeoX login-

panel.

In order to be able to use GeoX you need a username and a password.

Please consult your GeoX coordinator for your username and password.

Enter your username and your password and click OK. The system will

close the login-panel and open the GeoXplorer (see next page).

Problem Note – logging on: You might not be able to log on to GeoX for a number of reasons:

1\ You entered an incorrect username. 2\ You entered an incorrect password. 3\ All your GeoX licenses are in use.

For the two first reasons you will be asked if you want to retry. Retry, but this time with the correct username and password. If all licenses are in use, the system will show the name of the users that are active.


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The GeoXplorer The GeoXplorer is your window to the GeoX database. It gives you access

to assessments, lets you engage the GeoX tools and supports reporting

across analyses in the database. The GeoXplorer is also used to export and

import analyses.

The GeoX data is organized in a hierarchical basin-play-segment structure.

Basins can be divided into sub-basins and plays can be divided into part-

plays.

As noted earlier, the segment is the smallest assessment unit. Segments

are located within a play or part-play. Prospects, on the other hand, can

span multiple plays as prospects are defined as a collection of one or more

segments. Prospects can therefore also be located at either the basin or

the play level.

The GeoXplorer Assessment tab has two main panes: a left (“Folder”)

pane with a hierarchical tree and a right-pane with a list of the contents of

the selected elements in the left pane.

Analyses are the lowest level of the GeoX database hierarchy, and are only

shown in the right pane of the GeoXplorer. Analyses can be opened with a

double click or by entering the GeoXplorer File menu - Open command.

There are different icons for the different type of analyses in the GeoX

database. “ ” is the icon for segment folders and segment analyses.

“ ” is the icon for play folders and play analyses. There can be multiple

analyses in a folder.

AnalysesAlternate assessments of thesegment, prospect or play.

FoldersExploration

“targets" that contain analyses

Part-Play

Analysis in the A1 CB Segment folder.

Oracle database

Basin


FoldersExploration


Play

Segment

Prospect AnalysesAlternate assessments of thesegment, prospect or play.

FoldersExploration


Part-Play

Analysis in the A1 CB Segment folder.

Oracle database

Basin


FoldersExploration


Play

Segment

Prospect


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Detail - Versioning:

Analyses are in one of three states: Test, Approved or Historical.

There can be multiple analyses in the Test state, only one in the

Approved state and multiple in the Historical. Approved and

Historical analyses are read-only. When a new analysis is

approved, then the existing Approved analysis becomes Historical.

The version of the analysis is indicated on the analysis icon.

Security permissions define what part of the database you can see and

what you can do with the data that you see. Permission to create a new

basin or rename existing basins is always limited to one person or a small

group of persons.


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The basic play assessment workflow The play assessment workflow with GeoX can be divided into substantive

activities such as entering input estimates or reviewing results and

“housekeeping” activities such as creating and saving the play analysis.

The main housekeeping activities involve either accessing an analysis in

the database or creating a new analysis. The analysis is attached to a play

(part-play) folder. You need to create the play folder in the appropriate

location in the basin-play hierarchy if this has not already been done.

Play analyses must be saved explicitly as nothing is automatically saved.

Once the play analysis tool (gPlayR) has been launched and the system has

opened a play analysis, you are ready to start doing your analysis of the

Yet-To-Find (YTF) resources in the play.

The Calculation activity is more or less instantaneous. It involves having

the play analysis tool do the Monte Carlo simulation to produce

probabilistic estimates of number of accumulations in the play, in-place

and recoverable YTF, discovered and ultimate resources based on your

estimates of the relevant input variables.

There are seven overall play assessment input activities:

• Document: Editing documentation of the context, main attributes of

the play, and issues that have been considered or need to be reviewed.

Most of the documentation inputs have no direct impact on the

assessment results. However, documentation facilitates sharing,

maintenance and reuse of the analysis.

• Setup: Establishing global settings for the play analysis. These

settings involve what hydrocarbon phases are active, the limits (large

field minimum, resource minimum, etc) to be used, number of trials

and seed for the Monte Carlo simulation.

• Definition: Defining the model used to calculate the size and success

rate of postulated and mapped potential accumulation. Definition is

also used to enrol assessed prospects and discoveries in the play.

• Overall: Defining the estimated number of postulated and mapped

potential accumulations in the play in addition to some play-level

inputs such as areal extent of the play and the discovered resources in

the play.

• Risks: Entering estimates of the shared chance of adequacy of the

different factors that control the success of the play.

• Postulated & Mapped Features: Entering the volumetric and

conditional risk estimates for postulated and mapped features. The

features are assumed to have the same field size distribution and

conditional risks.

• Correlation: Entering estimates of the relevant across-features

correlation groups and correlations at the overall level of the play.


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There is a separate notebook tab for doing the Setup, Volume, Fluids,

Risks and Correlation inputs for the postulated (and mapped) features.

The input pages on this tab are identical to the pages for the corresponding

segment analysis notebook. The only exception is that there is only one

tab on the Analysis Setup page for the HC fluids.

Once the analysis has been calculated, you review the resulting estimates

of chance of success, in-place and YTF recoverable resources. Additional

results such as intermediate and yield estimates as well as the size-by-rank,

rosy future, variance diagram and resource diagram are used to reality

check (RC) and interpret the results: Do the results make sense? How do I

make sense of the results?


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The Rift Margin Carbonate Play The review of the basic play assessment workflow considers a couple of

part plays (B and E) in the West Sea rift margin carbonate play. The

primary assessment targets are an Early Cretaceous platform carbonate

reservoir that was deposited during the post-rift phase. The play is

unproven and the boundaries are defined by the limits of reservoir facies.

A recent seismic survey has enabled the delineation of six prospects (A1,

A2, A3, B1, B2 and B3) with segments in both the carbonate E part-play

as well as in an overlaying clastic reservoir play. The segments have been

assessed (see Table).

The only shared play risks in the Carbonate E (CB-E) part-play are

reservoir quality (0.9) and source and migration (0.8). We are confident

of both reservoir presence as well as the trap with sealing at the play level.

Segment Analysis

P(Discovery)

[%]

Oil Rec. Resources

Mean [million STB]

A1 CB Oil Only 25.9 105.3



B1 CB Oil Only 15.1 241

B2 CB Oil Only 20.2 189

B3 CB Oil Only 21.6 135.8 Table 1. Assessed segments in part play “CB-E”

Source and migration (0.8) is the only shared play risk in the Carbonate B

(CB-B)part-play. We will start the assessment with the CB-B part-play.


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Creating a play and a play analysis In order to create an analysis of thus part-play, you first need to create a

part-play folder for the part-play. The folder needs to be located correctly

in the basin-play structure of the GeoX database, in this case the East Sea

basin and the cret-cb play.

Basins are typically pre-defined as part of the process of setting up the

GeoX database. Permissions for creating new basins are limited. In our

case, the West Sea basin has already been defined. In order to create a

folder for the Carbonate B part-play:

1 Select the “cret cb” play and right click the mouse.

2 Select New part play.

3 Enter “CB-B” in the Add part play dialog box and click OK. The CB B

play has been added to the cret cb play.

4

You are now ready to create a play analysis of the CB B part-play.

GeoX supports the use of alternative templates for new analyses. A

template is an analysis that has been populated with pre-defined content in

terms of both analysis setup and data. Templates can have default values

for inputs with statistical distribution that match company best practice

workflows. Templates can have default correlations that are generally

valid. The template is selected when you create a new analysis

Your GeoX installation can have templates3 for doing play assessment.

Here we will use the GeoX default template.

1 Select the “CB B” part play and right click the mouse.

3 Templates are created in the GeoXplorer in the section under the Templates tab. They

can refer to any analysis under the Assessments tab of the GeoXplorer.


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2 Select New play analysis. The system opens the New play analysis

dialog box.

3 Select the “GeoX default values” public template.

4 Replace the default name of the analysis with the label “Postulated w.

Direct FSD” and click OK. The system opens a play analysis notebook

using the selected template.

Advice – play analysis names: The name of the play analysis should be brief, but descriptive. What differentiates this analysis from other analyses in the play folder? For a first analysis, it is often useful to name the analysis according to the type of volume modelling option that has been used – for example “Direct FSD OE”. Do not include part-play name, basin name, your initials, or the date. This information is defined by the name of the play folder that the analysis is attached to as well as the location of play in the basin-play hierarchy. GeoX provides a default analysis name (“Play analysis N”). The analysis name can always be changed later


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The play analysis notebook Once you have created a new play analysis the system opens the play analysis

notebook for the “Postulated w Direct FSD” analysis of the CB-B part play --

as indicated in the title bar of the notebook.

The notebook has a set of Input pages and a set of Results pages. You “write”

the Input pages with your input data and then “read” the Results once you

have gotten GeoX to calculate the results.

To write or read the pages, you browse the left hand page list. Some pages

have multiple tabs that give you access to the sub-pages. The Results are

organized in separate sections for In-Place results and Recoverable results.

You can browse directly to any page in the notebook, enter data in whatever

sequence you want. However, we recommend that you follow the workflow

implied by the structure of the input page sequencing.


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The play analysis notebook menu bar consists of two parts: The command

menus and the toolbar with a message field.

The toolbar gives rapid access to frequently used functions: Saving analyses,

printing analyses, viewing distributions, entering input parameter estimates,

calculating, setting the units, setting the presentation format and selecting the

currency. Using the Units toggle on the toolbar, you can instantly change

between Field Units and SI (Standard International) units. Changing units can

also be done using the View>Units from the Command menu.

Note

• Units can be set separately for Inputs and Results. Results units apply to

hydrocarbon volumes. The Units toggle sequences through the following

four alternatives:

You also use the toolbar buttons to switch between percent and decimal

representation of parameters (such as porosity, HC saturation, risks, etc) that

vary between 0 and 1.

The stoplight (Analysis status) indicator is green when analysis inputs and

analysis results are consistent (i.e. you have done a Calc after the most recent

input estimate edit).

Toggle Inputs Results

SI SI SI Field Field Field SI/Field SI Field Field/SI Field SI

Save Analysis

Edit parameter

Calculate

Toggle percent/decimal

Analysis status

View distribution

Toggle units

COMMAND MENU

TOOLBAR


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The Messages section gives feedback on verification issues that the program

has identified in terms of your analysis.

There are two main types of messages: WARNINGS (indicate by the yellow

warning icon) and ERRORS (indicated by the red error icon). Errors have to

be corrected in order to proceed with calculation (or other operation

involved); warnings are just that: the system is telling you that there is an

input that is unusual, but does not necessarily imply that something is wrong.

When you created the “Postulated w Direct FSD” analysis using sample

values, you get one error message. It is informing you that you need to define

a resource analysis – either a postulated or by enrolling an assessed

prospect/segment or by enrolling one or more discoveries. Double click on

the message in order to review the message text.


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Documenting a play analysis We recommend that you first enter a short documentation of your analysis.

The Summary tab of the Description page can be used for free-text

documentation. Typically you might want to include a brief overview of

the play and the play analysis. Examples of entries might be key

assumptions and critical uncertainties, key issues that need to be looked at

in more detail, etc.

Documentation is obviously important. It facilitates use, reuse and sharing

of analyses. A good analysis name can do a lot.


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The Properties sub-page covers the structured attributes that are used to

document the analysis. The properties complement the free-format

documentation that can be entered on the Summary sub-page.

Consider the case of the “Location” property (the properties available on

your installation will most certainly be different from the ones shown

here):

1 Select the property

2 Click Edit

3 Select the appropriate value from the list of Alternatives

4 Click OK


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The play analysis set-up The Setup page controls the stochastic (Monte Carlo) simulation and the

limits for the estimations done by the simulation. We will revisit these

attributes when we get to calculation.

WE WILL LOOK AT RESOURCE LIMITS AFTER ENTERING ESTIMATES FOR

POSTULATED PROSPECTS

.


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Saving the play analysis Play analyses are not automatically saved. We therefore recommend that

you do a save of your analysis at regular intervals in the workflow.

Start by saving your analysis once you have completed the set-up and your

initial documentation.

To save, click the Save button on the toolbar.

The system opens the Save analysis dialog box. The first time you save an

analysis you can edit the name of the analysis. You can also enter a

description of the main changes in the analysis relative to the previous

change. The system uses this information to provide a log of the changes.

The first time you save the analysis, the system enters automatically a text

that documents that the analysis was created in the database with this save.

In the case the analysis is based on a template, the change documentation

also includes the id of the template.


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After the save, you will see the new play analysis in the right-hand

window of the GeoXplorer.


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Overall Parameters We are now ready to start editing the estimates of the input parameters that

are attributes of the play as a whole. These estimates are entered on the

Overall, Risk and Correlation pages of the Main play analysis notebook

tab.

We start with the estimates that are entered on the Overall input page. The

most important is the estimates of the number of postulated features (there

are no mapped features in CB-B). We also enter an estimate of the areal

extent of the CB-B part-play. This latter estimate is used to calculate key

play performance indicators (such as yield and feature counts per square

km or 1000 acres).

Enter the area of CB-B (2000 km2) and an estimate of the number of

postulated features [stretched beta, 28, 40, 75].

We have opened a distribution viewer on the number of postulated

features. It shows that the distribution for the number of postulated

features is an integer distribution.


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Shared Play Risks The GeoX risk model can be customized to fit your company best practice.

Here we use the current default GeoX risk model with four risk factors.

The shared play risks are entered on the Risk page of the Main play

analysis notebook while the conditional risks are defined with the

postulated or in the enrolled assessed prospects.

For the CB-B part-play, the only shared play risks are associated is with

source and migration. The resulting overall chance of success of the play

(the marginal play probability) is 80%.

We are now ready to define the attributes of the postulated features.

Note

• If there are discoveries enrolled in the play analysis then the play risks

need to be set to 1.0.


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Defining the postulated features We are now ready to define the postulated potential features in the play.

To do this we need to create a template for the potential accumulations.

The template also applies to the mapped features. However, there are no

mapped features for the CB-B part-play.

The template is created on the Template tab of the Definition page.

1 Click Add on the Template tab of the Definition page.

2 Select the “New segment analysis...” to add a segment analysis

template. The system opens the “New postulated reservoir template”

selector.

3 Enter “Direct FSD” as the template name

4 Select the “Sample values” template values and click OK.

The system creates a new notebook tab for the postulated features labelled

“Direct FSD”.

Note

• Notice that once you have created the postulated feature tab, the error

message in the Message section (“no resource analysis defined”) is no

longer active.


23


The postulated feature inputs are identical to the Inputs of a segment

analysis. The only exception is that there is no setup page for the Monte

Carlo simulation with limits. This is here defined on the Main tab of the

play analysis notebook.


24


Postulated Setup We now are ready to enter the inputs that define the postulated potential

accumulation. We start with Setup where the postulated is defined as an

oil accumulation – i.e., as set by default.


25


Postulated Volume Inputs Browse to the Setup tab of the Volume page and select the “Direct

estimation of total volume” volume modelling option.

Select the Volume Parameters tab of the Volume page and enter an

estimate of the total volume (in OE) as a lognormal distribution with mean

of 56 MM STB OE, a standard deviation of 23 MM STB OE, and a low

end truncation at 10 MMSTB OE.


26


Similarly, enter an estimate of the GOR for the postulated on the Fluids

page (a uniform distribution with a minimum of 600 scf/STB and a

maximum of 900 scf/STB).


27


Conditional risks Enter estimates of the conditional segment risks on the Risk page. The

conditional risks are the probability that the geologic controls are adequate

for the individual postulated features – given that all the play controls are

OK.

For the postulated features of the CB-B part-play, we estimate that the

chance of adequacy of trap and seal is 60%, the chance of adequacy of

reservoir presence is 50%, the chance of adequacy of reservoir quality is

80% and the chance of adequacy of source and migration is 90%.

We see that the resulting overall conditional chance of success of a feature

(or what is labelled the conditional segment probability) is 21.6%. This

conditional chance is often also referred to as the Future Success Rate

(FSR) for the postulated features in the part-play (play).


28


Calculating YTF resources Having completed the inputs, you are now ready to have GeoX calculate

the corresponding estimates of chance of success, in-place resources and

recoverable resources for drilling out all the postulated features in the play.

On the Setup page set the Number of trials to 1000. The system will

simulate 1000 success cases where success is defined as when the play

works (in other words the shared geological controls work).

We set an economic screening threshold at 70 MM STB. The system will

report success volumes and risked YTF volumes above this threshold.


29


Reviewing and interpreting results The Results pages provide both the main results in terms of chance of

success as well as estimates of in-place and recoverable resources. In

order to further support verification and interpretation of results the system

shows a number of other reports and diagrams that we will review after an

initial review of the Recoverable Resources results.


30


Yet-To-Find Recoverable resources The Yet-To-Find (YTF) resources table in the Recoverable section is a key

result report.

.

The variables reported on are:

Number of postulated accumulations [integer] is the conditional number of

accumulations from postulated features assuming that the marginal play

probability is 1.

Number of mapped accumulations [integer] is the conditional number of

accumulations from mapped features assuming that the marginal play

probability is 1.

Number of enrolled accumulations [integer] is the conditional number of

accumulations from enrolled prospects (segments) assuming that the

marginal play probability is 1.

Number of accumulations [integer] is the conditional total number of

accumulations assuming that the marginal play probability is 1.

Note

• The "MC (N)-r" distribution type is a risked Monte Carlo distribution.

Unconditional number of accumulations [integer] is the risked total

number of accumulations.

Accumulation size [1e6 m3 OE or 1 e6 bbl OE] is the success amount of

recoverable hydrocarbons in an accumulation assuming that the marginal

play probability is 1.


31


Conditional prospect potential [1e6 m3 OE or 1 e6 bbl OE] is the risked

amount of recoverable hydrocarbon in an accumulation under the

assumption that the marginal play probability is 1.

Conditional B play YTF potential [1e6 m3 OE or 1 e6 bbl OE] is the YTF

amount of recoverable hydrocarbon expected to be found in the play under

the assumption that the marginal play probability is 1, that there exists at

least one undrilled accumulation in the play, and that all features are

drilled out. This success case estimate of the YTF play potential therefore

ignores that there are a finite number of targets available for drilling.

Conditional A play YTF potential [1e6 m3 OE or 1 e6 bbl OE] is the YTF

amount of recoverable hydrocarbon expected to be found in the play under

the assumption that the marginal play probability is 1 and that all features

are drilled out. This estimate of the success case YTF play potential should

be close to the B potential when there are a large number of features in the

play.

Unconditional play YTF potential [1e6 m3 OE or 1 e6 bbl OE] is the

risked YTF amount of recoverable hydrocarbons in the play if all features

in the play are drilled. If the marginal play probability is 1 then the

unconditional play potential and the conditional play potential are

identical.

Note

• The conditional play potential is the success volumes for the play, i.e.,

the Yet-To-Find volumes to be found given that the play works. The

unconditional play potential is the risked Yet-To-Find volumes in the

play – i.e., the conditional volumes risked by the chance of success of

the play.

Double clicking on the appropriate notebook cell opens a graphical display

and table of the output variable distribution.


32


Let us look at the distribution of the success case total number of

accumulations (in this case the same as the success case number of oil

accumulations).

We see that we are sure that there are at least 3 accumulations if the play

succeeds. There will not be more than 20 accumulations. The expected

number of accumulations is close to 10 (9.79). This is consistent with a

mean estimated 44.4 features and a conditional chance of success

(conditional segment probability or FSR) of 21.6% (44.4 * 0216 = 9.6

success case discoveries).

Let us now look at the estimated success YTF volumes (conditional A

potential) and risked YTF volumes (unconditional potential) in the play.

The mean success YTF volume is 551 MM STB OE. The risked YTF

volume is 441 MM STB OE. The difference reflects that there is a 20%

chance that the play does not work.


33


Above Screening Threshold YTF The Yet-To-Find (YTF) resources above the screening threshold are

shown in the Above Screening Threshold section. As the screening

threshold was defined as 70 MM STB oil, we need to look at the oil

results.

We see that the accumulation size is truncated at 70 MM STB. The results

indicate that only 1.49 accumulation above 70 MM STB. We also see that

there is a 23% chance that there are no accumulations above 70 MM STB.

The success case YTF potential above 70 MMSTB is approximately 128

MM STB.


34


Size-by-rank table and diagram The size-by-rank table and diagram provides an estimate of the size

distribution of the postulated accumulations in the play. The size-by-rank

distribution is based on the ranked size distribution of the accumulations in

the play obtained on a trial-by-trial basis. The output is the distribution

together with the mean and 90% confidence interval of the ranked

accumulation sizes.

We see that in CB-B part-play we expect that the largest accumulation has

mean resources of 100 MM STBOE. The P05 value for this largest

expected accumulation is 140 MM STBOE while the P95 value is

approximately 65 MM STBOE (the upper and lower values of the stick

plot).


35


Percent YTF volume-by-size diagram This diagram shows percent of the part-play YTF potential as a function of

size of accumulations in a log-probit format. The curve (in red) is the

percent of total YTF potential in accumulations that are larger than the

accumulation size indicated on the x-axis.

The blue curve is the inverse cumulative probability distribution for the

size of the YTF accumulations in the play.

From the diagram we can for example read that 10% of the total YTF

resources in the CB-B part-play are in accumulations with 100 MM

STBOE or larger.


36


More Functionality

This Primer has covered the basics of the GeoX functionality for assessing

the YTF resources in a play. There is a significant additional functionality

that we have not covered because it would take us beyond the scope of the

Primer. The most important elements not covered are:

• Enrolling discoveries and assessed features. This functionality lets

you estimate the YTF potential as the sum of the potential in

postulated, mapped and assessed features. By including discoveries

you can get a complete picture of the ultimate recoverable potential in

the play.

• Small fields. The estimates that we have considered cover large fields

– fields that have been explicitly counted, sized and risked. The play

tool also has a facility for projecting the number and size of fields in

the lower end of the field size distribution.

• Additional volume and fluids modelling options. As shown in the

simple example covered, the play tool makes use of the full range of

volume and fluids options available for modelling segments.

• Trial browsing. The trial browsing option enables you to inspect and

analyze all your Monte Carlo trials. This is useful when you want to

both verify and interpret your play assessment.

• Multiple scenarios. The gScenarioPlay tool enables you to do a

probabilistic aggregation of multiple alternative scenarios for your

play.

For situations where you want to consider play fairways with multiple

part-plays or when you want to estimate the YTF potential in areas of

interest with stacked plays, gPlaySum is the tool you need to consider.

This tool lets you do aggregation of plays while honouring all risk and

volume dependencies.


37


APPENDIX A: Play Analysis Inputs This appendix documents the play analysis notebook input pages.

The review does not cover input pages for all alternative volume and fluids

modelling options. However, the main input variables are covered.


38


About Setup Analysis The Analysis tab of the Setup page is used to set up the play assessment

method to be used for estimating YTF resources in the play. It is also used

to limits on resources and for defining the basis for estimating the small

field fraction potential in the play.

Sample size [selection list or integer number] defines the number of trials

to be included in the Monte Carlo simulation.

Initial seed number box [integer] defines the initial seed used when use

initial check box has been checked.

Use initial see check box [check] determines if the Monte Carlo simulation

is to use the seed defined in the initial seed number box.

Note

• Using the same initial seed assures that simulation runs have the same

series of random numbers.

Resource limits control low-end and high-end truncation as well as

estimation of resources above a screening threshold and potential

resources in small fields:

• Resource base minimum defines the minimum field size that is

considered when calculating the small field fraction.

• Large field minimum defines the minimum size of an accumulation

considered a success in the estimate of mapped and postulated features.

• Large field maximum defines a maximum field size that is considered

realistic given the exploration maturity of the play.

• Screening threshold defines the minimum economic volume required

in an accumulation.


39


The resource base minimum is used to estimate the small field fraction

YTF resources in the play. The small field fraction is the fraction of

resources in estimated accumulations below the large field minimum but

larger than the resource base minimum.

Small field extrapolation [Lognormal; Pareto; Exponential] is used to

choose the method for extrapolating small fields. Lognormal is the most

conservative (gives the least number of small fields) estimator while pareto

and exponential imply a "J" shaped field size distribution with potentially a

large number of small fields.

Notes

• Different limits will apply to oil (with associated gas) and gas (with

associated condensate) accumulations. Multiphase accumulations will

be classified as either oil or gas depending on the relative amounts of

oil and free gas in the accumulation.

• Estimation of small field fraction requires that you check both the

Resource base minimum and the Large field minimum.

Risk Model Template gives the label of the risk model template that has

been used with the analysis. Segment analyses that are enrolled in the play

analysis need to have the same risk model template if they are to be

aggregated in a prospect analysis.


40


About Definition: Enrolment4 Used to define the set of assessed discoveries and assessed prospects

(segments) that are enrolled in the play analysis.

The enrolment selector only permits enrolment of analyses of discoveries

and prospects (segments) in the play (part-play) that the play analysis is

attached to. You can only enrol a single analysis from each discovery or

prospect (segment).

The enrolment table shows the discovery date for the enrolled discoveries

as well as the estimated total OE resources in the discovery and the un-

risked OE resources in a prospect (segment). Discoveries are sorted

according to discovery date.

Prospects that have segments in the play can be enrolled. The play

analysis tool will use the play fractional estimates from the prospect that

are in the play.

Note

• Verification warnings will indicate whether enrolled segments and

prospects do not belong to the play (part play) that the analysis is

attached to. The enrolment selector supports enrolment across plays

and basins; enrolment errors are not caught before you try to calculate

the play analysis.

Analyses are enrolled by clicking the Add button. The system opens a data

base selector that is used to select the analyses to be enrolled.

Enrolled segments and prospects can be removed with a standard MS

Windows syntax: To remove all, select all by clicking on the first in the

4 Definition page is a part of the Advanced FSD option on the play analysis tool.


41


enrolment set, keeping down the CAPS key and then selecting the last in

the set. For removal of multiple analyses that are not contiguous, use hold

down the CTRL key.


42


About Definition: Discovery History Chart5 The chart shows the cumulative discovered OE resources as a function of

discovery sequence. With less than 10 discoveries each discovery is time-

stamped on the chart; with more than 10 discoveries, main intervals of

discovery dates are shown on the upper horizontal scale.

5 Definition page is a part of the Advanced FSD option on the play analysis tool.


43


About the Overall Parameters Together with the tab used to define the postulated and mapped features,

the inputs on the Overall page primarily define the inputs for the

calculation of total resources and Yet-To-Find resources in the play for

postulated and mapped potential features. Some overall input parameters

are used solely for estimating yield factors or other indicators of play

prospectivity.

Area of assessment unit [km2 or 1000 acres] is the areal extent of the play.

This parameter is only used to calculate resource and feature density

estimates.

Number of mapped prospects [integer] is the number of mapped potential

accumulations in the play that would be considered for drilling if the play

were to be fully explored.

Number of postulated prospects [integer] is the number of postulated

(speculative) potential accumulations in the play that would be considered

for drilling if the play were to be fully explored.

Note

• The distinction between mapped and postulated features is only used to

distinguish the basis for the estimates of number of potential

accumulations. In estimating the Yet-To-Find resources the mapped

and postulated prospects are lumped together and share a common

postulated template.

Conditional segment probability uncertainty multiplier is a factor that is

used to modify the estimated conditional segment probability estimate on a

play analysis trial basis.


44


Note

• In a single play analysis trial – where all prospects are drilled out, the

system uses the same value of the conditional segment probability

uncertainty multiplier. The mean of the uncertainty multiplier should

be 1.0 or else the multiplier will change the expected value of the

estimated conditional segment probability.

If Area Yield assessment method has been selected:

Area of assessment unit [km2 or 1000 acres] is the areal extent of the play.

Area yield [1e6 m3 OE/km2 or 1e6 STB OE/1000 acres] is the richness of

the play in terms of recoverable hydrocarbons per unit of area.

Feature density [number/km2 or number/1000 acres] is the number of

features that are potential accumulations per unit of area. This parameter

is used to generate an estimated number of prospects in the play.

Discovered resources [1e6 m3 OE or 1 e6 bbl OE OR 1e9 m3 GE or 1e9

scf GE ] is the discovered resources in OE (or GE) that have been

discovered in the play.

YTF threshold for effective assessment [1e6 m3 OE or 1 e6 bbl OE OR

1e9 m3 GE or 1e9 scf GE] is the YTF resources in the play that will define

a minimum amount of risked resources ( in OE or GE) that makes the play

an effective exploration opportunity.

Exploration efficiency [decimal or %] is a measure of the extent to which

the largest fields have been (or will be) discovered first. A discovery

sequence of ever decreasing field sizes represents 100% efficiency.

Random selection of prospects would result in an efficiency of 0%. A

discovery sequence where the smallest fields are discovered first has –

100% efficiency.

Note

• Exploration efficiency is currently not used in the play assessment. It

will be used to generate discovery sequences for predicting creaming

curves.


45


About Correlation (Postulated & Overall) The correlation page for the postulated internal FSD parameters is used to

specify how two or more input parameters that are used to define the size

of postulated potential accumulations are correlated.

Across Feature correlations are defined for individual parameters. They

are prefixed with “PLAY GROUP”.


46


The Play level sub-page is used to specify play level correlations in terms

of two or more overall play parameters and/or Play Group parameters that

have Across Feature correlations.

A statistically defined correlation varies between –1 and +1, where 0 is the

no correlation value (default). The intensity of statistical correlation is

indicated using a 9-point scale: Max negative, high negative, medium

negative, low negative, zero, low positive, medium positive, high positive

and max postive correlation. These intervals correspond to correlation

scores of –1.0, –0.9, -0.6, -0.3, 0.0, 0.3, 0.6, 0.9 and 1.0.


47


About Setup HC fluids modelling (postulated) The HC fluids tab of the Setup page of the postulated template is s used to

indicate what HC phases for the postulated. The choice of HC phase

defines the relevant subset of input parameters that are active on the

Volume and Fluid Input pages. Together with the volume set-up and the

fluid set-up, these setups define the ACTIVE PARAMETER SET in the

postulated template.

The "oil, gas, OR multiple phase" option defines a case where mutually

exclusive alternative HC phase scenarios are active. If the HC phase

risking option is active in the risk model, then you enter the relative

probability of the different phase outcomes on the HC phase risking sub-

page of the Risk Input page.


48


About the Volume Setup (postulated) This setup page is used to select among alternative approaches to

modelling rock volumes and hydrocarbon pore volumes in postulated

potential accumulations.

There are two alternative approaches for direct entry of hydrocarbon

volumes:

1) Direct entry of Field Size Distribution (FSD) estimate of hydrocarbon

volumes for each active phase

2) Direct entry of Field Size Distribution (FSD) estimate of OE (Oil

Equivalent) hydrocarbon volumes. With this alternative you also need

to enter an estimate of GOR and condensate yield on the Fluid page.

The alternative approaches for modelling hydrocarbon pore volume are:

3) Direct entry of net rock volume estimate.

4) Direct entry of gross rock volume estimate and an estimate of the net-

to-gross ratio.

5) Direct entry of estimates of area of closure, reservoir thickness, a

geometric factor and the net-to-gross ratio.

6) Direct entry of estimates of area of closure, reservoir thickness, column

height, closure length-to-width ratio, closure flat-top ratio and net-to-

gross ratio. The system computes a geometric factor on a trial-by-trial

basis.

7) Direct entry of estimates of the net-to-gross ratio and a function that

describes the relationship between the height of the hydrocarbon

column height and gross rock volume


49


8) Direct entry of estimates of the net-to-gross ratio and a function that

describes the relationship between height of hydrocarbon column,

closure area at top of reservoir and reservoir thickness

In addition to the estimate of net rock volume under closure, there is a

need to indicate how much of this volume is filled with hydrocarbons in

order to calculate the hydrocarbon pore volume. In the 3 first approaches,

you enter directly an estimate of the percentage of the net rock volume

under closure that is filled with hydrocarbons (trap fill). When modelling

rock volumes as a function of depth and as a function of hydrocarbon

column, area and thickness (alternatives 7 & 8), you also need to enter the

HC water contact (OWC or GWC) column as well as the column height to

the closure’s spill point.

In cases with multiple HC phases, you also need to indicate either the

share of HC pore volume that is free gas (alternatives 3, 4, 5 and 6) or the

gas oil contact (GOC) column (alternatives 7 & 8).


50


About Volume with Area, Thickness & GF (postulated) The volume page defines the main inputs for hydrocarbon pore volume

estimation for postulated potential accumulations using a depth-

independent representation. With this option, you enter area of closure,

reservoir thickness and geometric factor (GF) as a basis for calculating the

gross rock volume.

Area of closure [km2 or 1000 acres] is the area within a trap above the

spill point. A minimum threshold value is required.

Reservoir Thickness [m or ft] is the possible range for the thickness of the

reservoir, or the amount of vertical closure in a situation where structural

amplitude is less than individual reservoir thickness.

Geometric factor [fraction or %] is a correction factor that accounts for the

thinning of a full hydrocarbon column at the edge.

Note

• If you do not have an estimate of the geometric factor, consider using

the modelling option where you enter estimates of thickness, column,

Length-Width and Flat Top fraction of the structure.

Net/Gross Ratio [fraction or %] is the proportion of the reservoir thickness

made up of sand.

Porosity [fraction or %] is the amount of interconnected void space in the

reservoir rock.

Trap Fill [fraction or %] is the trapped hydrocarbon volume as a

percentage of the porous volume under closure.


51


Gas Fraction [fraction or %] is the relative proportion of the filled net rock

volume (NRV x Trap Fill) that is made up of gas.

Oil Saturation [fraction or %] is the oil saturation.

Gas Saturation [fraction or %] is the gas saturation.


52


About Volume w. Area-thickness_in_Table (postulated) The volume page defines the main inputs for hydrocarbon pore volume

estimation for postulated potential accumulations using a depth-dependent

representation. The inputs are entered on two sub-pages labelled "Depth

vs Area table" and "Other Volume Parameters". Depth is here column

height.

The Depth vs Volume diagram tab provides a graphical representation of

the GRV as input in the Depth vs Area table. The Trap Geometry Graph

tab provides a graphical representation of how area and thickness vary

with column height.

Gas Oil Contact [meters or feet] is the height the gas column in a

multiphase potential accumulation.

HC Water Contact [meters or feet] is the height the hydrocarbon column. .

Spill Point Depth [meters or feet] is the height of the column from crest to

spill point of the closure.

Notes

• Sampling of HC column height between the column intervals in the

Area and Thickness = f(column height) table is done by interpolation.

For columns larger than the largest in the table, the last value is used.

Depth [meters or feet] is the column height of the corresponding area

estimate. The crest of the closure is when the column has a height = zero.


53


Area [km2 or 1000 acres] is the estimated area of the structure at the given

column .

Thickness [meters or feet] is the isochore reservoir thickness at the specific

column.

In the Monte Carlo simulation, volume realizations are derived from

interpolation between the input columns. There are three choices of

interpolation:

• AREA: Linear interpolation of areas. Implies that area changes

linearly between heights in table. Does not have any shape

assumptions.

• RADIUS: Linear interpolation of radius in areas as if the areas were

circular, hence assuming that the radius is changing linearly between

the column heights in the table. The method does not assume a strictly

circular shape of structure, but it does assume that the shape of the

structure does not change between column height intervals.

• COMBINED: A combination of Area and Radius. The method

assumes the shape of a running field (two semi-circles attached to the

short sides of a rectangle). A new input parameter, Length-Width

Ratio, describes the shape of the area. A higher Length-Width Ratio

results in a more oblong shape. Length-Width Ratio equal to one gives

a circular shape.

The interpolation method affects the area at a column height between two

input column height intervals, and the total volume. The chosen method

may impact the estimated GRV significantly.

54

About the Fluids Setup (postulated) The entries on the Set-up tab of the Fluids page is used to select among the

alternative representations of the parameters that define surface condition

HC resources: Either formation volume factors or gas expansion/ oil

shrinkage factors; Either direct entry of wet gas shrinkage factor or

indirect entry via a proportionality factor between condensate yield. In

addition there is an option to input functions that define the formation

volume factors as well as secondary phase yields as a function of reservoir

depth. The fluids page is also used to define recovery factors.

Reservoir parameters can be modelled either by direct entry of the

parameter values or indirectly using equations that define how the

reservoir parameters vary with reservoir depth.

For direct entry of reservoir parameters:

Formation factors. Used to select among the alternative representations of

the parameters that define surface condition HC resources:

EITHER as formation volume factors

OR as gas expansion/ oil shrinkage factors

Wet Gas Shrinkage. Used to select between direct entry of a wet gas

shrinkage factor or indirect entry via a factor that models wet gas

shrinkage as proportional to condensate yield.

55

About Fluids parameters using Direct Entry (postulated) The Fluids page defines, together with the volume page, the main inputs

for estimation resources at surface conditions. The active fluids

parameters are defined on the Fluids Setup page.

Oil Form. Factor (Bo) [m3/Sm3 or bbl/STB] is the oil formation volume

factor. This is a number greater than 1.0

Oil Shrink. Factor (1/Bo) [Sm3/m3 or STB/bbl] is the oil shrinkage factor.

This is a number less than 1.0.

Gas Oil Ratio [Sm3/Sm3 or scf/STB] is the ratio of associated gas to oil.

Gas Form. Factor (Bg) [m3/million Sm3 or cf/million scf] is the gas

formation volume factor. This is a number less than 1.0

Gas Expans. Factor (1/Bg) [Sm3/m3 or scf/cf] is the gas expansion factor.

This is a number greater than 1.0

Wet Gas Shrinkage Factor [decimal or %] defines how much of the dry

gas remains after removal of the condensate liquids phase (100% means no

shrinkage).

Condensate Extraction Factor [Sm3/million Sm3 or STB/million scf]

defines the relationship between condensate yield and the wet gas

shrinkage.

Note

• With the option to enter wet gas shrinkage indirectly by entering the

Condensate Extraction Factor (CE), then the wet gas shrinkage is


56


computed = (1 – (Condensate Yield/ CE)). The default value for CE

(1666) is a good empirical estimator of the relationship between

condensate yield and wet gas shrinkage.

Condensate Yield [Sm3/million Sm3 or STB/million scf] is the yield of

condensate from wet gas.

Recovery Factor Oil [fraction or %] is the amount of oil in-place that can

be recovered.

Recovery Factor Assoc. Gas [fraction or %] is the amount of associated

gas in-place that can be recovered.

Recovery Factor Gas [fraction or %] is the amount of in-place non-

associated gas that can be recovered.

Recovery Factor Condensate [fraction or %] is the amount of condensate

in-place that can be recovered.

57

About Fluids parameters using Equations (Postulated The Fluids page with the Setup for reservoir parameters as a function of

reservoir depth is used to define the depth dependent reservoir parameter

functions.

The fluids equations define Oil Formation Volume Factor (Bo), Gas

Formation Volume Factor (Bg), the Gas Oil Ratio (GOR) and the

Condensate yield (CGR) distributions as a function of reservoir depth.

Reservoir depth is defined as stochastic estimate.

There are 6 depth related fluid parameters:

• Original reservoir pressure (Pe) [bars or psi]

• Reservoir temperature (T) [Deg K or R]

• Gas-Oil Ratio (Rs) [ sm3/sm3or scf/STB]

• Oil Formation Factor (Bo) [sm3/sm3or bbl/STB]

• Gas Compressability (Z) [real]

• Condensate Yied ( C) [sm3/1000 sm3or STB/1000 scf]

These variables are modelled as a function of depth using one of four

different functional forms: Zoned linear, exponential, power and

logarithmic. Each function is expressed using two parameters A and B that

describe the depth gradient (A) and a constant (B). In the zoned linear

there is a depth parameter in addition to the A and B parameters for each

zone.


58


Depth floor [m or feet] is an estimate of at what depth oil cracks into gas.

It is used to estimate the probability that the depth of reservoirs are below

the depth floor. This latter estimate affects the relative probability of oil

and gas accumulations.

59

APPENDIX B: GLOSSARY This is a short glossary of key terms used in the GeoX play assessment

tools (unique GeoX terms labelled with a GeoX reference).

Assessment unit

The basic building block for assessment of the YTF hydrocarbon resource

potential in an area of interest (AOI). In play assessment, the basic

assessment unit is either a play or a part-play. The YTF potential in the

area of interest is the aggregate of the potential in all the assessment units.

See also Play; Part-play.

Accumulation

An individual body of naturally occurring petroleum in a reservoir. Also a

connected hydrocarbon reservoir. See also Feature.

Conditional Play Potential (GeoX)

Estimated success case YTF hydrocarbon resources in a play. The

condition is that all shared geological controls at the play-level are

adequate. See also Conditional A Play Potential; Conditional B Play

Potential.

Conditional A Play Potential (GeoX)

The success case YTF potential in the play that includes outcomes where

the play succeeds, but where none of the counted or assessed features

succeed (in other words when one or more of the conditional geological

controls are not adequate).

Conditional B Play Potential (GeoX)

The success case YTF potential in the play that only includes outcomes

where there is at least one accumulation (discovery). The conditional A

and the conditional B potential are the same in cases where there are a

large number of postulated, mapped and assessed features or where the

conditional segment probability (FSR) is relatively high.

Conditional segment probability (GeoX)

Probability that a potential accumulation succeeds. For postulated

features, this is the same as the Future Success Rate. See also Future

Success Rate.

Exploration efficiency

A measure of the extent to which the largest fields have been (will be)

discovered first. A discovery sequence of ever decreasing field sizes

represents 100% exploration efficiency. Random selection of prospects

would result in 0% efficiency. A sequence where the smallest fields are

discovered first implies a negative exploration efficiency.

Feature

A lead, prospect, field, discovery, dry test that all have in common that

they represent a discrete and distinct configuration of geology that has

been predicted or proven to be suitable for containing hydrocarbons. See

also postulated feature; mapped feature.


60


Feature-based approach

Feature-based approach to assessment of the success case YTF resource

potential in a play is based on estimating the number of potential features,

their independent chance of success (FSR) and their size (the size of the

corresponding field). For frontier plays with limited information, we use

analogs to postulate both the number of potential accumulations and their

size. In mature plays, the YTF potential is the sum of the resources in

each of the assessed prospects in the play – if we assume that we have

been able to map and assess all the prospects. See also Discovery process

approach; Area yield approach; Postulated feature.

FSR

Future Success Rate. Future Success Rate

Chance of success of a postulated or mapped feature in a play (part-play)

given that the play works (all the shared geological controls are adequate).

See also conditional segment probability.

Large field (GeoX)

Field that is counted, risked, and seized explicitly. Distinguished from

small field where the count and seizing is projected from the estimates for

the large fields. See also Small field; Small field fraction.

Large field maximum (GeoX)

No future discoveries larger than this maximum are expected in the play.

The count of postulated and mapped features is for fields less than the

large field maximum and larger than the large field minimum. See also

Large field; Large field minimum; Feature based approach.

Large field minimum (GeoX)

Size of smallest large field that is counted and risked. When using

estimates of count from calibration area, then large field minimum is size

for which no future discoveries larger than this minimum are expected in

the calibration area.

Mapped feature

A feature that has been located, but that has not necessarily been assessed.

See also Postulated feature; Prospect; Feature.

Marginal play probability (GeoX)

Probability that all the shared play controls are adequate. This probability

is estimated by the product of the probability that each of the shared

controls are adequate. Failure of one or more shared geologic controls

means that the play does not work. A play with one or more discoveries

has a marginal play probability of 1.0.

Part-play (GeoX)

A sub-division of a play that is given a separate folder in GeoX. Part-

plays can be further sub-divided into part-plays. If the play folder

represents a play fairway, then the part-play can represent a common play


61


element where all the shared play risks are identical. See Play; Play

fairway.

Play

A play is a delineated area containing a collection of potential

accumulations (postulated as well as mapped and assessed exploration

targets), accumulations (fields) and dry tests with shared regional geologic

controls on source, migration, reservoir and trap.

Play fairway A play fairway defines an area with similar shared geologic controls on the

occurrence of hydrocarbons. A play has identical shared geologic controls.

The play fairway therefore is broken down into plays or part-plays that

capture the regional spatial variability in shared geologic controls.

Postulated features

Features that have not been located (mapped), but that are assumed to be in

the play. Sometimes called conceptual features. Typically we get

estimates of the postulated features in a play by using a relevant analog as

a basis. Alternatively we might have an area within the play with good

data. The estimate from this calibration area is projected to the whole area

of the play. See also Mapped feature.

Resource minimum (GeoX)

Smallest field of potential interest.

Size-by-rank diagram (GeoX)

Provides an estimate of the size distribution of the largest, next to laregest,

etc predicted fields in the play. The size-by-rank distribution is based on

the ranked size distribution of the accumulations in the play obtained on a

trial-by-trial basis. The size-by-rank is generated for the postulated and

mapped features that succeed.

Small field (GeoX)

A field smaller than Large Field Minimum and larger than Resource

Minimum. Small fields are projected from the estimates of the number

and size of the large fields. GeoX offers three different algorithms for the

projection. They reflect different assumptions concerning the distribution

that best describes the overall field size distribution: lognormal, Pareto

and exponential. See also Large field; Large Field Minimum; Resource

minimum

Small field fraction (GeoX)

The fraction of the total Yet-To-Find resources in the play that are

estimated to be in small fields (fields with a size greater than the Resource

minimum and larger than the Large field minimum).

Unconditional play potential (GeoX)

The risked Yet-To-Find resource potential in the play. The unconditional

estimate also includes the outcomes where the play fails and the outcomes

where there are no discoveries event though the all the shared geological


62


controls in the play are adequate. For a proven play the conditional and

unconditional play YTF potential are identical. See also Conditional play

YTF potential.

Yet-To-Find resources

Undiscovered resources in the play or other area of interest. Denotes the

resources that might be discovered if all the features in the play are drilled

out.

YTF resources

Yet-To-Find resources in play or larger assessment unit.

%YTF volume-by-size diagram (GeoX)

Diagram that shows the percent of the Yet-To-Find resources in the play as

a function of the size of the YTF accumulations.

Documents

Doing Yet-To-Find Resources YTF with GeoX 5.8 JUL… · GeoX is a collection of assessment tools designed to support and promote high quality exploration decisions. It focuses the