Overview of a geophysicist workflow.

Prince Felix Igweze. (Covenant University) 2015.

Prince Felix Igweze.Department of Physics – Applied Geophysics.

Covenant University.

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IT Trainee at Orion EnergyJuly 2015.


SAFETY AWARENESS

Please put cell phones on silence to avoid distractions.

In case of any electrical or safety hazard quietly gather at the muster point.


OBJECTIVES.

• To gain a fundamental understanding of these disciplines through theoretical and practical approach.

• To interact with various professional, getting an insight on work flow of various disciplines.

• To get a first hand understanding of team integration across various disciplines in the quest to explore for oil/gas resources.


GEOLOGY(Ogheneworo Offeh)

GEOPHYSICS(Goodluck Oboh/Mr Gbenga)

PETROPHYSICS.(Azubikwe Ndupu)

GEOMODELLING.(Ogheneworo Offeh)

Reservoir Engineering.(Adewale Taiwo/Damilola Olabimtan)

Prince Felix(Intern, Orion Energy)

REPORTING PROCESS.


AT THE END OF THIS PRESENTATION YOU SHOULD :

Have a fundamental understanding of various oil exploration disciplines and workflow.


QUOTE

A man who moves a mountain is a man who start by carrying small stones – Confucius


WHAT IS GEOLOGY ?

Geology is the study of the earth surface and interior, and how they give rise to the featuresThat we observe today.


SEDIMENTARY PROCESS

SEDIMENTS : Unconsolidated (“loose”) granular geologic material.

SEDIMENTARY ROCKS: Rocks formed by the breakdown of preexisting rocks by physical process that resolve to their erosion, consolidation and digenesis.


TYPES OF SEDIMENTS

1. Terrigenous clastic sediments

2. Carbonate sediments.

3. Evaporites.

4. Iron stone

5. Phosphate rocks.

6. Silliceous sediments.

7. Volcanic sediments.

1. Sandstone

2. Limestone

3. gypsum

4. Hematite

5. Phosphate


DEPOSITIONAL ENVIRONMENTSTERRESTRIAL TRASITIONAL MARINEAlluvial fan Delta complex Marine

Braided river Beach Submarine fan

Meandering river Lagoon Basin

Lake Dunes


ALLUVIAL FAN

• Fan shaped deposit of water transported material.• Formed when fast flowing streams flattens, slow and spreads.• It has 3 zones : Proximal, Intermediate and Dital grains.

Alluvial fan

BRAIDED RIVER

Resurrection river, Alaska.Example of a braided river.

• Exist near mountainous regions.• Occurs in rivers with high slope.• Formed when threshold level of sediment load or slope is reached. causing streams to split and the formation of braided channel shape.


DELTA.

• Landforms created at the mouth of a river where that river flows into an ocean, sea, estuary, lake.

• Formed by deposition of sediments by rivers.

• Divided into DELTA FRONT (Sand bars) and DELTA PLAIN (Channels bay and food plain).

• Types include: River, Wave and Tide dominated deltas.

Delta Lagoon Meandering riverIn Sacramento, USA.


Syncline. Anticline Isocline

FOLDS : When sedimentary strata are bent or curved as a result of plastic deformation.

LimbAxial Plane


Overturned fold. Recumbent fold Chevron fold

Anticline

A fold in seismic section


FAULTS are planar fractures in rocks in which the rock on one side of the fracture has moved with respect to the other.

Fault terminologies


MAJOR TYPES OF FAULT MOTION

Strike slip fault.

Normal fault

Reverse fault

Fault in seismic section.

Graben


RESERVOIRS .

A subsurface pool of hydrocarbons contained in porous of fractured rock formation.

FEATURES OF A RESERVOIR.

1. Oil and gas source rock.

2. Migration.

3. Reservoir rock.

4. Seals.

5. Traps.A typical oil/gas reservoir.


SOURCE ROCK

• Rocks from which hydrocarbon have generated from.

• Types : 1. Formed from algae remains (Generate waxy crude oil). 2. Formed from marine planktonic remains (Produce both oil and gas). 3. Formed from terrestrial plants. (Produce light oil, e.g coal and coaly shales).

MIGRATION

• Oil and gas move away from source rock.

• Porosity is required for movements.

• Classified into secondary and primary migration.


RESERVOIR ROCKS

• Contains connected pore spaces used to reserve the fluid inside.

• In the oil industry sedimentary rock are the most important reservoir rocks.

PHYSICAL CHARACTERISTICS OF A RESERVOIR

1. Depth.

2. Area and thickness.

3. Porosity.

4. Permeability.


SEAL CAP

• An impermeable rock that forms a seal around reservoir rock

• Examples : Shales and Evaporites

TRAPS

• Configuration of rock suitable for containing hydrocarbons

• Types : 1. Structural traps 2. Salt-dome traps 3. Stratigraphic traps 4. Combination traps


The most successful man is the average man with laser like focus – Bruce Lee


OUTLINE.Definition of seismic interpretation.

General overview

Seismic Acquisition

Seismic Processing

Seismic Interpretation

Seismic interpretation workflow. Things to know before interpretation Reflectivity Polarity. Wavelet and phaseness. Synthetic seismogram.


Simply put, seismic interpretation is a geophysical technique used in the extraction of subsurface information from seismic data.

WHAT IS SEISMIC INTERPRETATION ?

A 2-D Seismic Line Image.


GENERAL OVERVIEW.

Exploration Seismology is divided into 3 parts :

Seismic Acquisition.

Seismic Processing.

Seismic Interpretation.

Weight drop

Vibroseis


SEISMIC DATA ACQUISITION.

• Energy Sources are used to generate shockwaves.

• Subsurface formation reflect waves.

• Reflections are recorded by geophones/hydrophones in traces.

Geophone

Hydrophone cable

t = 0

SEISMIC DATA PROCESSING.

Distance

Time

Time taken to reach a certain layer


A Basic Seismic Line

SEISMIC TRACE

• Represents response of elastic waves to velocity and density contrast across layers of rock

SEISMIC NOISE

• Anything other than the desired signal e.g environment noise, diffraction, refraction, multiples.

SEISMIC RESOLUTION

• Ability to distinguish between two sedimentary sequences on a seismic section.


OBJECTIVES OF SEISMIC PROCESSING.

• To improve signal to noise ratio mainly through CMP stacking.

• To improve vertical resolution mainly through deconvolution.

• To improve lateral resolution mainly through migration aka imaging.


SEISMIC INTERPRETATION.

• Seismic data comprises of seismic images.

• Images represent lithological boundaries of the subsurface

• Lithological boundaries vary in acoustic impedance.

• Understanding of the subsurface how it affect wave reception is required.

Seismic shot gather captured by geophones 2.5m apart.


1. Base Map : Shot point location.

2. Seismic section : Inclines and crossline.

3. Available wells.

4. Velocity data from wells : From check shot and VSP.

5. Formation top of the well : To determine the well.

6. Logs and reports.

TO START INTERPRETATION WE MUST HAVE :


REFLECTIVITY.

• Reflections are recorded from velocity or density contrast in the rock sequence.

POLARITY (Reverse and Normal Polarity).

THINGS TO KNOW BEFORE SEISMIC INTERPRETATION.

• The state of having two opposite tendencies.

• The normal and reverse polarity are based on positive amplitude (peaks) and negative amplitude (trough).

• In seismic we have two types of polarity: Reverse and normal polarity


WAVELETS AND PHASENESS.

Minimum Phase Wavelets: Short time duration and concentration of energy at the start. It has a minimum point / energy at time 0.

Zero Phase Wavelets: Shorter duration than the minimum phase equivalent. Wavelet is symmetrical with a maximum point / energy at time 0.

• Wavelets are used to describe short time series.

• The two most important are: Minimum and zero phase wave form

Minimum phase wavelett

zero -phase wavelet Zero phase wavelet.


SYNTHETIC SEISMOGRAM (SYNTHETIC).

• A direct one dimensional model of acoustic energy travelling through the layers of the earth.

• Derived from convolving reflectivity from logs (density) with wavelet from seismic data.

• Helps to improve seismic interpretation.


CHECKSHOT SURVEY.

• Used to measure travel time from surface to known depth

• P wave velocity can be measured by lowering geophone to desired depth, sending energy and measuring resulting signals

• From this we can estimate time (velocity/depth) and plot in time/depth scale

VERTICAL SEISMIC PROFILING (VSP).

• Used for correlation with surface seismic data

• Produces higher resolution of the seismic surface

• Measurements are made in a vertical well bore, geophone are inside the bore


REFLECTION COEFFICIENT.

• This is the ratio of the amplitude of the displacement of a reflected wave to that of the incident wave

12

12

1122

1122

ZZZZ

vvvvR

Mathematically:where:•ρ = rock density•υ = rock velocity•1 = parameters above the interface•2 = parameters below the interface

ACOUSTIC IMPEDENCE.

• Acoustic impedance (Z) = density (ρ) χ velocity (V)


WORKFLOW

Scan/Load Seismic Data

Well to Seismic Tie(VSP/Synthetic Seismogram/Checkshot)

Fault Interpretation

Interpret/Map Horizon/Regional Marker

Generate Time Maps/Grids

Depth Conversion

Volumetrics(Calculate GRV/Estimate STOIIP)

Proposed Wells(Appraisal/Development)

Literature Review

Velocity Analysis (TZ)

Attribute Extraction

Petrophysical Input.

Load/QCWell Data.

Field Wide Correlation


1. SCAN/LOAD SEISMIC DATA.

An Exabyte tape.2. QUALITY CHECK WELL DATA.

• Seismic sections• Available well data (well log and formation tops)• Velocity data of wells (from check shot and VSP)

• Well header• Deviation survey• Wireline logs.• Check for polarity, identify peaks, through and zero crossing• Check for phaseness


3. WELL – TO – SEISMIC TIE.

• Create synthetic seismogram to know formation top the tie with seismic section.

• From well, we know the depth of the event (Formation tops).

• Plotting values to depth and time (check shot) we can extract values of time for certain depth (to mark depth on seismic section).

• Allows well data measured in depth to be compared to seismic data measured in time.


PROCEDURES FOR PICKING FAULTS.

Define a fault frame work or fault plane by tying together with horizontal plane sections.

Initialize control with vertical and horizontal sections.

Finding and marking structures on the horizon

Pick major faults on vertical sections

Fault segments

Horizon picking

Fault Polygons


INTERPRETATION / MAP HORIZON / REGIONAL MARKERS.

• In geology, horizon refers to either a bedding surface where there is marked change in lithology.

• In the interpretation of seismic reflection data, horizons are the reflectors (or seismic events) picked on individual profiles.

• These reflectors represent a change in rock properties across a boundary between layers of rock, particularly seismic velocity and density.

Fault Polygons


PICKING AND INTERPRETATION OF HORIZONS.

• Horizons can be picked according to the time of the occurrence in the seismic section.

• Since horizons on sections are so much, interpretation is done in grids. Starting from those close to the well.

• When picking our horizons we put the strength and continuity of events into consideration.

• We use our inline and crossline to accurately map out our horizons.

Picking of horizon on seismic data.

• Determine formation top and bottom


SEISMIC ATTRIBUTE.

• This are quantities extracted from seismic data that can be analyzed in order to enhance information that might be more difficult to depict in traditional seismic image..

• Primary attributes analyzed on seismic data include: Two way time travel. Amplitude. Frequency. Phase difference.

• This attributes help to enhance information such as lithology, horizons, faults etc.


DEPTH CONVERSION.

• Depth conversion is an important step of the seismic reflection method, which converts the acoustic wave travel time to actual depth, based on the acoustic velocity of subsurface medium (sediments, rocks, water).

• The two broad categories of depth conversion are:

Direct time depth conversion.

Velocity modelling for depth conversion.

PETROPHYSICAL INPUTS

STOIIP (Stock Tank Oil -Initially - In – Place): This is the volume of oil in a reservoir prior to production.

This could be achieved using Checkshots, Synthetic seismogram or VSP.


GENERATION TIME MAPS/GRIDS.

• Time Maps: These is a seismic data consisting of equal elevations in time.

TWO WAY TIME MAP (TWT).

• Take values of horizon at each shot point.

• Put values at line on base map.

• Repeat step at each line.

• Loaf fault polygon on map

• Contour values to get two way time map.


VELOCITY MAP

• Put the average velocity determined at each well.

• Repeat for each well and contouring velocity values to get velocity map.

DEPTH CONTOUR MAP

• Extract depth values from velocity and two way time map.

• Depth converted maps shows the depth of intersected horizon.


VOLUMETRICS / PROPOSED WELLS.

THE VOLUMETRIC EQUATION

STOIIP = GRV * Net/Gross Ratio * Porosity * Oil saturation * (1/Bo)

GIIP = GRV * Net/Gross * Porosity * Gas saturation * (1/Bg)

Recoverable oil = STOIIP * Recovery factor for oil

Recoverable gas = GIIP * Recovery factor gas

HCPV (Hydrocarbon pore volume) = GRV * Net/Gross Ratio * Porosity * HC saturation

GRV = Area * Depth

These are used to place appraisal wells


Fall Seven times and stand up eight – Japanese Proverb


RESERVOIR ENGINEERING.


OVERVIEW

What is reservoir engineering?

Role in an asset management team.

Tools used by a reservoir engineer.

Who can become a reservoir engineer.

Reservoir engineering workflow.


WHAT IS RESERVOIR ENGINEERING ?

• This is carried out by a reservoir engineer.

ROLES IN AN ASSET MANAGEMENT TEAM.

• To make initial estimate of the volume of hydrocarbon in a reservoir.

• To take account of any volume during production.

• To determine how long a reservoir can produce.

• Plan on most optimized way to produce wells.

• Reservoir engineering is the application of science to optimize the recovery of oil and gas.


TOOLS THAT HELP IN ANALYSIS.

WHO CAN BECOME A RESERVOIR ENGINEER.

• Anyone with a Bachelors degree or Masters in petroleum engineering can become a reservoir engineer.

• A bachelors degree in petroleum engineering consist of courses in reservoir engineering, production engineering, drilling engineering, geology and fluid mechanics,

• Entry level requirements require a bachelors or masters degree in petroleum engineering.

• Eclipse.

• Sclumbeger PVTI.

• Eclipse Office.

• Prosper.

• Saphir

• MBA


RESERVOIR ENGINEERING WORKFLOW.

Data QC and validation

Review of reservoir parameters

Production performance analysis

PVT analysis

Material balance calculation

Well performance (Nodal) analysis

SCAL analysis

Dynamic model construction and simulation


DATA QC AND VALIDATION.

REVIEW OF RESERVOIR PARAMETER.

• Review parameter of different time periods for consistency.

• Parameters include : Pressure, temperature, production data, static model.

• Check data for the required field.

• QC is done with respect to convention and previously produced reservoirs in the field.

• List of data we QC are : 1. PVT report. 2. Historical pressure data. 3. Historical temperature data. 4. Production data.


PRODUCTION PERFORMANCE ANALYSIS.

• Receive data and make a plot over time, make deductions about the historical performance of the reservoir.

• Example of data received include : Gas oil ratio (GOR), Water cut profile, reservoir pressure profile, oil and gas rate.

PVT ANALYSIS.

• Analysis is carried out and certain parameters are gotten. These include : Gas Oil Ratio (GOR). Formation Volume Factor Oil (Bo). Formation Volume Factor Gas (Bg).


MATERIAL BALANCE CALCULATIONS.

• Used to determine the drive mechanism.

• These drive mechanisms are the main contributors to pressure.

• Examples of such drive mechanisms include :

Gas drive. Solution drive. Gravity drive. Rock and liquid drive. Water drive.


WELL PERFORMANCE (NODAL) ANALYSIS.

• Its purpose is to build a replica of the well for dynamic simulation.

• Depicts the well properties in the dynamic model.

• Used to show how different wells perform in each part of the reservoir.

SCAL ANALYSIS.

• SCAL : Special Core Analysis.

• Involves evaluating the relative permeability, how formation contents will move with respects to other contents present.

• It gives real permeability curve, capillary pressure curve.

• It tells us how fast or slow the fluid moves.


DYNAMIC MODEL CONSTRUCTION AND SIMULATION

• Data gotten from the previous steps are incorporated into the static model for dynamic simulation.


OVERVIEW

Mission of a petrophysicist

Log interpretation an log types

Basic steps in quick log interpretation.


MISSION OF A PETROPHYSICIST.

To identify the quality resources in the subsurface.

To provide evaluation of the nature of formations fluid and rock properties.


LOG INTERPRETATION.

• A SONDE is used to measure formation properties as a function of depth.

• The recorded curves are called wireline logs.

LOG TYPES.

Logs can be classified in three families:

Reservoir Thickness : Non Reservoirs from reservoirs.(Gamma ray and spontaneous potential)

Porosity : Calculate porosity, identify lithology and differentiate oil from gas.(Density, Neutron, Sonic logs.

Resistivity: Used to calculate hydrocarbon saturation.(Laterolog, Induction and micro resistivity log).


RESERVOIR THICKNESS LOG.GAMMA RAY LOG.

• This is the most commonly used reservoir thickness log.

• The gamma radioactivity of a formation can be used to discriminate between reservoir and non reservoir.

• Reservoir rocks )Sandstone, Limestone, Dolomite) contain none or small amount of radioactive elements (K, Th, U).

• Non reservoir rocks contain large amounts.

High radioactivity.

Low radioactivity.


• The gamma ray log helps to determine reservoir net/gross.

• NET/GROSS RATIO: The ratio of the total amount of pay footage to total thickness of reservoir.

RESISTIVITY LOG.

• Calculation of hydrocarbon saturation.

• Resistivity is measured on logs based on resistivity of rock minerals, fluids and hydrocarbon.

• Hydrocarbon bearing zones have high resistivity.

• When resistivity measurement is carried out, measurements can be affected by mud filtrate that have invaded the formation zone.

• Three different resistivity measurements are taken to negate this effect and measure the true formation resistivity.


THESE MEASUREMENTS ARE:

LLD : (Laterolog deep) Looks deep into the reservoir. It is hardly influenced by the mud cake and uninvaded zone. It will usually read the resistivity of the uninvaded zone (Rt).

LLS : (Laterolog shallow) Looks shallow into the reservoir and measures the resistivity of the invaded zone. It is influenced by the mud cake and invaded zone and can e used to correct the LLD.

MSFL : (Micro spherically focused log). Reads the resistivity of the invaded zone close to the well bore.


POROSITY LOG.

DENSITY LOG.

• The tool works in such a way that it emits gamma ray from a device into the formation.

• The density is directly proportional to the electron density and inversely proportional to the gamma rays.

• From the electron density the bulk density is calculated.

Summary of Quick look evaluation.


BASIS STEPS IN QUICKLOOK LOG EVALUATION.

1. Review the logs. - Review quality of the wireline logs. - Use logs from surrounding well to identify anomalies.

2. Identify reservoir rocks (Gamma ray). - Discriminate potential reservoir rock from non permeable rock. - Intervals with low GR are probably sand (reservoir) and intervals with high GR are probably shale (non reservoir).

3. Discriminate hydrocarbon zones (Resistivity + density/neutron). - Water-bearing zones are characterized by low resistivity and oil-bearing zone vice versa.

4. Gas/Oil differentiation. - We can discriminate gas and oil bearing intervals by looking for high density/neutron separation in our log.

• Prince Felix Igweze. (Covenant University) 2015.

5. Calculate porosity and confirm lithology. (Density/Neutron). - We calculate porosity using the density log, possibly in combination with the neutron log.

Porosity (ɸ) = (ῤma - ῤLOG) / (ῤma - ῤfl)

ῤma = Matrix Density.

ῤLOG = Density Log.

ῤfl = Fluid Density.

• In hydrocarbon bearing zones we approximate the invaded zone fluid density (ῤfl )using the mud filtrate density and an estimated hydrocarbon density with:

ῤfl = 0.7ῤmf + 0.3ῤhc


ARCHIE EQUATION.

• The amount of hydrocarbon can be calculated via water saturation obtained from resistivity log using the Archie equation.

THE ARCHIE EQUATION FOR WATER-BEARING ROCK.

• In a clean water bearing reservoir, all pore spaces is filled with formation water.

• The total resistivity of water bearing zone (Ro) depends on the resistivity of the water (RW), the amount of water

present (equal to Ǿ) and the shape of water body (cementation factor : m)

• Thus the first Archie equation: Ro = RW Ǿ-m


ARCHIE EQUATION FOR HYDROCARBON - BEARING ROCK.

• In a hydrocarbon bearing zone part of the water is replaced by oil and gas.

• Total resistivity also depends on water saturation (Sw) and geometry of coating grains (n).

I = Rt / Ro = Sw -n

• “I” (Resistivity Index) – Increase of the resistivity of the hydrocarbon filled rock over resistivity of the water filled rock.

THE COMBINED ARCHIE EQUATION.

• The combined equation gives the following equation which describes how actual measured resistivity depends on water resistivity.

Rt = Rw Ǿ -m Sw -n

Rt = Resistivity of hydrocarbon nearing zone.


6. ESTABLISH WATER RESISTIVITY RW

• We can find this by taking average values of entire water bearing intervals and apply the first Archie equation.

Rw = Ro Ǿ-m

7. CALCULATE WATER SATURATION SW IN HYDROCARBON BEARING RESERVOIR (RESISTIVIT/POROSITY).

• Calculate the hydrocarbon saturation, Sh , from the combined Archie equation.

Rt = Rw Ǿ -m Sw -n

Sh = 1 - Sw

• If there are no water bearing interval, Rw can be estimated using local well data, regional knowledge, the SP log or measurements from water samples taken from the formation in nearby well.


8. REPORTING.

• The following information are summarized by for each major reservoir and fluid type:

1. Total net hydrocarbon sand count.2. Average porosity.3. Average hydrocarbon saturation.4. Observed fluid contacts and sources.5. Petro physical parameters used.6. Special considerations and peculiarity of the evaluation.


REFRENCE.

http://homepage.ufp.pt

http://www.slideshare.net

Wikipedia.com


THE END

Overview of a geophysicist workflow.

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Transcript of Overview of a geophysicist workflow.