This document discusses methods for estimating hydrocarbon volumes in oil and gas accumulations, including deterministic and probabilistic volumetric estimation methods. Deterministic methods average reservoir property data from wells, cores, and seismic to estimate field-wide properties, while probabilistic methods use statistics and analog data to predict trends away from sample points. Accurate reserve estimates are important for evaluating an oil and gas company's value and longer-term prospects. The document provides terminology and formulas for calculating metrics like STOIIP and GIIP using data on reservoir area, thickness, porosity, water saturation, and gas formation volume factor.

1. HC estimation methods
(just Geologist method)

2. other methods ?

3. Introduction
Volumetric estimationis concerned with quantifying how much oil and gas exists in an
accumulation.
The estimate will vary throughout the field lifetime as
 More informationbecomes available
 The technology for gathering and interpreting the data improves.
A volumetric estimateis therefore a current estimate, and should be expected to change over
time.
Two main methods of estimating volumetrics are used;
1. Deterministic
2. Probabilistic.

4. 1. Deterministic methods average the data gathered at points in the reservoir, from
 well logs,
 cores,
 seismic,
to estimate the field-wide properties.
2. Probabilistic methods use predictive tools, statistics, analogue field data and input regarding
the geological model to predict trends in reservoir properties away from the sample points.

5. Commercial Application
The volumetrics of a field, along with the anticipated recovery factors, control the reserves in
the field; those hydrocarbons which will be produced in the future.
The value of an oil or gas company lies predominantly in its hydrocarbon reserves which are
used by shareholders and investors as one indication of the strength of the company,
both at present and in the future.
A reliable estimate of the reserves of a company is therefore important to the current value as
well as the longer term prospects of an oil or gas company.

6. 1. Deterministic Method
Volumetric estimates are required at all stages of the field life cycle.
In manyinstances a first estimateof "how big" an accumulation could be is requested.
If only a "back of the envelope" estimateis needed or if the data available is very sparse a quick
look estimation can be made using field wide averages.
"back of the envelope" ::: done quickly to provide a rough estimate

7. Some terminologies

8. Thickness (h) : the isochore thickness of the total interval ("gross thickness") regardless of
lithology.
 An isochore map displays lines of equal thickness in a layer where the thicknesses are
measured vertically.
Isochore maps in geology are also referred to as True vertical Thickness (TVT) maps
Net sand : the height of the lithologic column with reservoir quality, i.e. the column that can
potentially store hydrocarbons.
NOS : the length of the net sand column that is oil bearing.
GRV : is the gross rock volume of the hydrocarbon-bearing interval and is the product of the
area (A) containing hydrocarbons and the interval thickness (h)
GRV =A . H
Units : ([ft3] or [acre.ft] or [m3])

9. Isopach vs isochore
An isopach is a line that connects points of equal true thickness (i.e. measured perpendicular to
bedding), whereas...
An isochore is a line that connects points of equal vertical thickness.
INCLUDE THIS SLIDE IN MAPPING

10. STOIIP
GIIP
Sw
Bg
Bo

11. Formuale
STOIIP
GIIP •7758 = conversion factor from acre-ft to bbl
•43560 = conversion factor from acre-ft to ft3

12. When and how to get
the data ?

13. Area
The area can be measured from a map.
There are two methods:
 Depth
 Thickness

14. Depth method

15. Thickness method

16.  h :: drilling ,coring, logging
 Sw or So : coring, logging
 Bg or Bo :: coring, fluid samples and testing.

17. ACCURACY
Dependent on quality of reservoir description.
Reserves estimates often high because this method does not consider problems of reservoir
heterogeneity.

18. Problem:
A reservoir has following properties.
A= 1214.057 hectres
h= 9.144 m
Porosity= Φ = 0.15
Swi= 20%
T=150 F
Pi = 2600 psi
z= 0.82
Bgi= ?
Calculate
◦ Reservoir Pore volume
◦ GIIP
CONVERSIONS
1 HECTRE = 2.47 ACRES
1 m = 3.28 ft
R = F + 460
=0.00543 𝐟𝐭 𝟑/𝐬𝐜𝐟