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.

Reservoir Fluid Properties?

What are reservoir fluids? Crude oil Natural gas or Drinkable water?

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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

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

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.

ROCK MATRIX AND PORE SPACE

Rock matrix Water Oil and/or gas

Framework

Matrix

Cement

Pores

Sand (and Silt) Size Detrital Grains

Silt and Clay Size Detrital Material

Material Precipitated Post-Depositionally,During Burial. Cements Fill Pores andReplace Framework Grains

Voids Among the Above Components

FOUR MAJOR COMPONENTS OF SANDSTONE

MATRIXFRAMEWORK

(QUARTZ)

FRAMEWORK(FELDSPAR)

PORE

0.25 mm

CEMENT

FOUR COMPONENTS OF SANDSTONE

PDC Cutters

Fluidvent

Drill collarconnection

Inner barrel

Outer barrel

Thrust bearing

Core retainingring

Core bit

CORING ASSEMBLY AND CORE BIT

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.

Coring

• Whole core sampler

• Side-wall core sampler

Whole Core Photograph,Misoa “C” Sandstone,

Venezuela

WHOLE CORE

Photo by W. Ayers

SIDEWALL SAMPLING GUN

Core bullets

Core sample

Formation rock

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.

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.

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

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

WHOLE CORE ANALYSIS vs. PLUGS OR SIDEWALL CORES

PLUGS OR SIDEWALL CORES

Coring

core plug

whole core

INFORMATION FROM CORES

Porosity

Horizontal permeability to air

Grain density

Vertical permeability to air

Relative permeability

Capillary pressure

Cementation exponent (m) and saturation exponent (n)

Standard Analysis Special Core Analysis

*Allows calibration of wireline log results