This document discusses reservoir rock properties and how core samples are used to characterize reservoirs. Reservoir rocks must have porosity and permeability to store and transmit fluids. Core samples provide information on lithology, porosity, permeability and other properties essential for evaluating a reservoir's fluid storage and flow capabilities. Whole core samples are most representative but sidewall cores provide additional data points. Both core types are analyzed to understand factors like relative permeability needed for reservoir modeling and production forecasting.

1. Introduction
 What are the reservoir rock properties?
 The importance of reservoir rock & fluid
properties
 How fluids flow through the reservoir rock
and how this flow can be altered to produce
greater recovery and profits
 Provides good understanding in reservoir
management, Simulation and EOR, etc.

2. Reservoir Fluid Properties?
 What are reservoir fluids?
 Crude oil
 Natural gas or
 Drinkable water?

3. Reservoir Rocks
 Oil created by the source rock won’t be useful unless
it winds up being stored in an easily accessible
container, a rock that has room to “suck it up”
 A reservoir rock is a place that oil migrates to and is
held underground.
 Examples of reservoir rocks includes:
 Sandstones
 Limestone and /or Carbonate rocks

4. Characteristics of Reservoir Rocks
A good reservoir rock must have porosity
in which petroleum can exist. Even though a
reservoir rock looks solid to the naked eye,
a microscopic examination reveals the
existence of tiny openings in the rock, called
pores.
Another characteristics of reservoir rock is
that it must be permeable. That’s the
pores of the rock must be connected
together so that hydrocarbons can move
from one pore to another

5. Source of data: Coring
 Coring are processes used to recover formation samples from
petroleum reservoirs.
 Reservoir rock samples are used for reservoir description and
definition, reservoir characterization and to enhance both geological
petrophysical nature of the reservoir.
 Physical sample of reservoir rock core is essential to evaluate the two
most significant characteristics:
 the capacity and ability of the reservoir rock to store and conduct
petroleum fluids through the matrix.
In addition, data on formation’s lithology and production potential
are obtained through coring program.

7. ROCK MATRIX AND PORE SPACE
Rock matrix Water Oil and/or gas

8. FOUR MAJOR COMPONENTS OF
SANDSTONE
Framework
Sand (and Silt) Size Detrital Grains
Matrix
Silt and Clay Size Detrital Material
Cement
Material Precipitated Post-Depositionally,
During Burial. Cements Fill Pores and
Replace Framework Grains
Pores
Voids Among the Above Components

9. MATRIX
FOUR COMPONENTS OF SANDSTONE
FRAMEWORK
(QUARTZ)
FRAMEWORK
(FELDSPAR)
PORE
0.25 mm
CEMENT

10. CORING ASSEMBLY AND CORE BIT
PDC Cutters
Fluid
vent
Drill collar
connection
Thrust bearing
Outer barrel
Inner barrel
Core retaining
ring
Core bit

11. Coring
Unlike a normal drill bit, which crushes
the rock into small pieces, a core bit can
be visualized as a hollow cylinder with
cutters on the outside.
The cylinder of rock that is cut by the bit
is retained within the core barrel by an
arrangement of steel fingers or slips.
Core diameters are typically from three
to seven inches and are usually about 90
feet long.
• Whole core sampler
• Side-wall core sampler

12. Whole Core Photograph,
Misoa “C” Sandstone,
Venezuela
WHOLE CORE
Photo by W. Ayers

13. SIDEWALL SAMPLING GUN
Core bullets
Formation rock
Core sample
The sidewall sampling tool can be used to
obtain small plugs from the formation.
The tool is run on a wireline after the hole
has been drilled. Some 20 to 30 bullets
are fired from each gun at different
depths.
The hollow bullet will penetrate the
formation and a rock sample will be
trapped inside the steel cylinder. When
the tool is pulled upwards, wires
connected to the gun pull the bullet and
sample from the borehole wall.
Sidewall cores are useful for identifying
hydrocarbons zones, when viewed under
UV light. Qualitative inspection of
porosity is possible; however, the cores
may have been crushed during the
collection process, so quantitative
sampling of porosity is questionable.

14. SIDEWALL CORING TOOL
Coring bit
Samples
A newer wireline tool
actually drills a plug
out of the borehole
wall, thus avoiding
crushing of the
sample.
Up to 20 samples can
be individually cut
and are stored inside
the tool.

15. WHOLE CORE ANALYSIS vs.
PLUGS OR SIDEWALL CORES
WHOLE CORE
 Provides larger samples
 Better and more consistent representation of
formation
 Better for heterogeneous rocks or for more complex
lithologies

16. WHOLE CORE ANALYSIS vs.
PLUGS OR SIDEWALL CORES
PLUGS OR SIDEWALL CORES
 Smaller samples
 Less representative of heterogeneous formations
 Within 1 to 2% of whole cores for medium-to high-porosity
formation
 In low-porosity formations,  from core plugs tends to
be much greater than  from whole cores
 Scalar effects in fractured reservoirs

17. Coring
whole core
core plug

18. INFORMATION FROM CORES
Standard Analysis Special Core Analysis
 Porosity
 Horizontal permeability
to air
 Grain density
 Vertical permeability to air
 Relative permeability
 Capillary pressure
 Cementation exponent
(m) and saturation
exponent (n)
*Allows calibration of wireline log results