1 Introduction

Instructor: Graham Webber

18/11/2015

Petrophysics: Definition

• “The study of rock properties and their interactions with fluids.”

• “The description of oil and or gas distributions and the production flow capacity of reservoirs, from interpretations of pore systems and fluid interactions using all available data.”

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The aim…

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Requirements for a hydrocarbon reservoir

• Source rock• The origin of the hydrocarbons trapped in

the reservoir is organic material in shales. The source rock is not necessarily in direct contact with the reservoir.

• Reservoir rock• A rock with both storage capacity and the

ability to allow fluids to flow is required to store the hydrocarbons.

• A seal• A seal is required since without it the

hydrocarbon would be lost from the reservoir over geological time.

• Hydrocarbons migrate upward from the source beds until they escape to surface or are trapped by an impervious barrier.

• Oil and gas accumulates by expelling water from the porous rocks.

Gas

Oil

Water

Impermeable bed

Porous bed

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Reservoir Rocks

• In nearly all cases reservoirs are found in sedimentary rocks:

• Clastics – composed of fragments of rock• Sandstones• Conglomerates• Silts• Shales

• Biogenic• Coal• Reef limestone

• Chemical• Chalk • Limestone• Dolomite• Evaporite

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Origin of sandstones: clastic depositional environm ents

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Component rocks in clastic reservoirs

• Sandstone (most often)• SiO2 (quartz)

• Shale• Silicate rock with small

particle sizes silt-clay.

• Contain a variable clay component.

• Contain organic material.

Reservoir rock

Non-Reservoir rock& Seal

Source Rock Sediments containing organic material: Shale

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Component rocks in carbonate and evaporite reservoi rs

• Limestone• CaCO3

• Dolomite• MgCa(CO3)2

• Tight limestone or dolomite

• Halite (Salt)• NaCl

• Anhydrite • CaSO4

• Shale

Reservoir rock

Non-Reservoir rock& Seal

Source Rock Sediments containing organic material: Shale8

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Carbonate depositional environments

Petrophysical data

• Logging while drilling data• Wireline logs• Core coverage and depth shifts• Core data

• Conventional • Special

• Formation pressure data• Directional survey data• Formation tops• Fluid contacts• Formation evaluations• Perforation intervals• Etc

The petrophysicist is responsible for building and maintaining a database of all of the petrophysical data for a field or prospect.

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Petrophysics: What do we interpret from well logs?

• Depth• Location of permeable formations• Porosity• Thickness of reservoirs• Net Sand / Net Pay• Subsurface Pressures• Fluid phases, gas, oil, water• Fluid saturations Sw, So, Sg

• Moveable Hydrocarbons• Depth of formations• Environment of Deposition• Lithology• Temperature• Velocity/Time• Seismic responses• Correlation with other wells

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Petrophysics place in the subsurface world

Petrophysics

Geology-reference depths

-rock composition

-deposition

-facies

Geophysics-sonic and density

-fluid subsReservoir

Engineering-permeability

-saturation-height

-pressure

Drilling-logging and

sample planning

-pore pressure

Production

Technology-well completion

design

-perforation depths

Geomechanics-rock strength

-stress orientation

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Petrophysics contribution to calculating hydrocarb on in place

Stock Tank Oil initially in place STOIIP

Gross rock volume GRV

Gross reservoir ` G

Net reservoir N Logs, well tests, core (permeability)

Porosity Ø Logs, core, (stressed porosity)

Water Saturation Sw Logs, core, (Archie m & n, Dean Stark SwSaturation-height (core capillary pressure)

Oil Formation volume Factor B0 PVT lab measurements (generally between 1 and 2)

Geophysicist Geologist Petrophysicist Reserv oir Engineer (PVT)

0

1)1(

BS

G

NGRVSTOIIP w •−•••= φ

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The petrophysicists contribution to Reservoir model ling

• Modelling a reservoir is a complex and integrated task.

• Petrophysics contributes in many ways:

• Clay/Shale Volume (a key for well correlation and facies determination).

• Porosity estimation at well locations.

• Water Saturation at well locations.

• Estimates of Rock Types or Facies.

• Permeability estimates and models.

• Saturation Height relationships models.