RESERVOIR PETROPHYSICS

PETE 311

PETROPHYSICS

Petrophysics is the study of rock properties and rock interactions with fluids (gases, liquid hydrocarbons, and aqueous solutions).

Modified from Tiab and Donaldson, 1996, p. 1

RESERVOIR PETROPHYSICSPETE 311

COURSE DESCRIPTION

Systematic theoretical and laboratory study of physical properties of petroleum reservoir rocks

• Lithology• Porosity• Compressibility• Permeability • Fluid saturations• Capillary characteristics• Rock stress• Fluid-rock interaction

RESERVOIR PETROPHYSICSCourse Objectives

By the last day of class, the student should be able to:

1. Define porosity; discuss the factors which affect porosity and describe the methods of determining values of porosity;

2. Define the coefficient of isothermal compressibility of reservoir rock and describe methods for determining values of formation compressibility;

3. Reproduce the Darcy equation in differential form, explain its meaning, integrate the equation for typical reservoir systems, discuss and calculate the effect of fractures and channels, and describe methods for determining values of absolute permeability;

 

RESERVOIR PETROPHYSICSCourse Objectives

4. Explain boundary tension and wettability and their effect on capillary pressure, describe methods of determining values of capillary pressure, and convert laboratory capillary pressure values to reservoir conditions;

5. Describe methods of determining fluid saturations in reservoir rock and show relationship between fluid saturation and capillary pressure;

6. Define resistivity, electrical formation resistivity factor, resistivity index, saturation exponent, and cementation factor and show their relationship and uses; discuss laboratory measurement of electrical properties of reservoir rocks; and demonstrate the calculations necessary in analyzing laboratory measurements;

RESERVOIR PETROPHYSICSCourse Objectives

7. Define effective permeability, relative permeability, and permeability ratio; reproduce typical relative permeability curves and show effect of saturation history on relative permeability; illustrate the measurement of relative permeability; and demonstrate some uses of relative permeability data.

8. Describe three-phase flow in reservoir rock and explain methods of displaying three-phase effective permeability.

9. Demonstrate the techniques of averaging porosity, permeability, and reservoir pressure data.

10. Demonstrate capability to perform calculations relating to all concepts above.

11. Design and conduct experiments to determine porosity, rock compressibility, absolute and relative permeability, fluid saturation, capillary pressure, and electrical properties of reservoir rocks; analyze and interpret experimental data; and prepare laboratory reports.

(These are minimum skills to be achieved/demonstrated)

PETROPHYSICS

• Why do we study petrophysics?

Cross Section Of A Petroleum System(Foreland Basin Example)

Overburden Rock

Seal Rock

Reservoir Rock

Source Rock

Underburden Rock

Basement Rock

Top Oil Window

Top Gas Window

Geographic Extent of Petroleum System

Petroleum Reservoir (O)

Fold-and-Thrust Belt(arrows indicate relative fault motion)

EssentialElements

ofPetroleum

System

(modified from Magoon and Dow, 1994)

O O

Sed

imen

tary

Bas

in F

ill

O

Stratigraphic Extent of

PetroleumSystem

Pod of ActiveSource Rock

Extent of Prospect/FieldExtent of Play

Timing of formation of the major elements of a petroleum system, Maracaibo basin, Venezuela.

PETROLEUM SYSTEM

From Schlumberger Oilfield Glossary

DEFINITIONS - SEDIMENTARY ROCK

Sedimentary Rock

Clastic Sedimentary Rocks (Such as Shale, Siltstone, and Sandstone)Consist of Broken Fragments of Pre-Existing Rock (cf. Detrital)

Carbonate Sedimentary Rocks (andEvaporites) May Form by ChemicalPrecipitation or Organic Activity

Rock Formed from the WeatheredProducts of Pre-Existing Rocks andTransported by Water, Wind, and Glaciers

CLASTIC AND CARBONATE ROCKS

Clastic Rocks

Consist Primarily of Silicate Minerals

Are Classified on the Basis of:

- Grain Size - Mineral Composition

Carbonate RocksConsist Primarily of Carbonate Minerals

(i.e. Minerals With a CO Anion Group)

- Predominately Calcite (Limestone) - Predominately Dolomite (Dolomite

or Dolostone)

3-2

Classified by Grain Size and Texture

Relative Abundances

Mudstone(Siltstoneand shale;

clastic)~75%

Sandstoneand conglomerate

(clastic)~11%

Limestone andDolomite

(carbonate) ~14%

SEDIMENTARY ROCK TYPES

Grain-Size Classification for Clastic Sediments

Name Millimeters Micrometers

BoulderCobblePebbleGranuleVery Coarse SandCoarse SandMedium SandFine SandVery Fine SandCoarse SiltMedium SiltFine SiltVery Fine SiltClay

4,096256644210.50.250.1250.0620.0310.0160.0080.004

500250125

623116

84

(modified from Blatt, 1982)

Commonly, phi-sizes are used for sediment analysis

Carbonate rocks can be classified according to the texture and grain size.

DUNHAM’S CLASSIFICATION - CARBONATES

From Schlumberger Oilfield Glossary

SealReservoir

rock

Seal

Migration route

Oil/watercontact (OWC)

Hydrocarbonaccumulation

in thereservoir rock

Top of maturity

Source rock

Fault(impermeable)

GENERATION, MIGRATION, AND TRAPPING OF HYDROCARBONS

Seal

DESCRIBING A RESERVOIRStructural Characterization

This structural trap is formed by an anticline and a normal fault. From Schlumberger Oilfield Glossary

STRUCTURAL HYDROCARBON TRAP

Closure. In map view (top), closure is the area within the deepest structural contour that forms a trapping geometry, in this case 1300 ft [390 m]. In cross section A-A', closure is the vertical distance from the top of the structure to the lowest closing contour, in this case about 350 ft [105 m]. The point beyond which hydrocarbons could leak from or migrate beyond the trap is the spill point.

DOMAL TRAP

From Schlumberger Oilfield Glossary

• Are hydrocarbons in this field oil or gas? • What is the volume of hydrocarbons In this trap?• What are the reserves?

A reservoir-drive mechanism whereby the oil is driven through the reservoir by an active aquifer. As the reservoir depletes, the water moving in from the aquifer below displaces the oil until the aquifer energy is expended or the well eventually produces too much water to be viable.

WATER DRIVE

From Schlumberger Oilfield Glossary

What is the DriveMechanism?

A gas-drive system utilizes the energy of the reservoir gas, identifiable as either as free or solution gas, to produce reservoir liquids.

GAS EXPANSION DRIVE

From Schlumberger Oilfield Glossary

What is the DriveMechanism?

Are there other drive mechanisms?

TYPES OF HYDROCARBONS

• Composition

• Molecular structure

• Physical properties

PHYSICAL PROPERTIES OF HYDROCARBONS

• Color• Refractive Index• Odor• Density (Specific Gravity)• Boiling Point• Freezing Point• Flash Point• Viscosity

FLUID DENSITY

˚ API = 141.5

= specific gravity

- 131.5

˚ API = API gravity

• What are the standard reporting conditions?

FLUID VISCOSITY

• Importance

• Units – centipoises (μ, cp)

• Strongly temperature dependent

• Standard reporting conditions

Drillship Jackup Submersible Land RigSemisubmersible

DRILLING RIGS

From Schlumberger Oilfield Glossary

From Schlumberger Oilfield Glossary

ROTARY DRILL BIT, WORN

RESERVOIR POROSITY

Definition: Porosity is the fraction of the bulk volume of a material (rock) that is occupied by pores (voids).

• Origins and descriptions

• Factors that effect porosity

• Methods of determination

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