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ESTIMATION AND
CLASSIFICATION OF
RESERVES OF PETROLEUM
OVERVIEW
Reserves(Petroleum) are the amount of crude oil,
natural gas that can be produced profitably in the
future from subsurface reservoirs
Making a good estimate of recoverable resources is
crucial to a company’s financial position since future
recovery is a measure often used to ascertain a
company’s borrowing future worth.
Depending on the scope of their operation, operators
of oil and/ or gas properties require estimates of
reserves and judgment about the degree of uncertainty
in those estimates
Of concern in the estimation and classification of
reserves are:
• Potential resources of crude oil
• Volume and degree of uncertainty of reserves on prospects being developed,
• Sizing and design of equipment to process reserves and transport them to market, and
• Opportunities for additional profit from incremental reserves that might be attributable to stimulation of producing wells,infill drilling, equipment modifications or additions, or improved recovery projects
Overview (2)
UNCERTAINTIES IN RESERVOIR ESTIMATES
Estimates of oil and/ or gas from subsurface reserves are controlled to
a significant degree by the heterogeneities of the reservoir
The degree of uncertainty in estimates of reserves depends
mainly on
The degree of geologic complexity
Maturity of the property,
The quality and quantity of geologic and
engineering data,
The operating environment, and
The skill, experience and integrity of the
estimators
Definitions of Petroleum Fluids
• Petroleum is a general term to apply to all
naturally occurring mixtures of predominantly
hydrocarbons. Petroleum includes natural gas ,
crude oil, and natural bitumen.
• Crude oil is the portion of petroleum that exists
in the liquid phase in natural underground
reservoirs and remains liquid at atmospheric
conditions of temperature and pressure
Classification crude oil
• Crude oil may be subclassified as: extra heavy
(stock-tank gravity less than 10° API), heavy
(stock-tank gravity 10 to 22.3°API), MEDIUM
(stock tank gravity 22.3 to 31.1°API).
• Crude oilk also has been classified as
naphtheric, mixed base, or paraffinic. This
classification is based on a characterisation
factor determined from density and atmospheric
boiling point curves.
Classification natural gas
• Natural gas may be subclassified as
associated or nonassociated gas.
Associated natural gas is found in contact
with or dissolved in, crude oil in a natural
underground reservoir.Nonassociated
natural gas is found in a natural
underground reservoir that those not
contain crude oil
Classification
• Solution gas, also(incorrectly) called
casing head gas is natural gas that is
dissolved in reservoir oil under initial
reservoir cnditions of pressure and
temperature and that is liberatedfrom
solution by reduction in pressure and
temperature as the oil is produced through
surface gas/oil separation equipment
Classification
• Lease condensate
Also called condensate or distilllate, is a
petroleum liquid consisting mostly of
pentanes and heavier that is in the
gas(vapor) phase under initial reservoir
conditions and that condenses to the liquid
phase when the gas is produced
Classification
• Plant Products
Plant products are petroleum liquids and associated products that have been extracted from lease gas at a central plant generally utilising absorption and/ or refrigeration processes. Plant product typically include ethane, propane, butane, and heavier components reffered to as natural gasoline
CLASSIFICATION OF RESERVES
• Because reserves of oil and/or gas are the commercially recoverable portion of accumulations of fluid hydrocarbons in the spaces of rocks, estimates of reserves should always be qualified to indicate the degree of uncertainty. The most used qualifiers are “proved,””probable”and “possible,”
• Generally procedures to estimate and classify reserves(ECR) have been described as deterministic or probabilistic
methodology
deterministic Procedures
Typically use the “best estimate” of the “true
value” of each relevant imput parameter in
a data set to calculate for each data set, a
single “best estimate” of reserves. Such
reserves, or part of such reserves, may be
classified as proved, probable, and/ or
possible.
Probabilistic Procedures
Typically use the full range of potential
values of each relevant input parameter in
a data set to calculate, for each data set, a
set of reserve estimates that reflect the
frequency distribution of the basic data.
Lehee’s Classification
A. Proved