Geology for Drilling Engineers_Rev0

8/11/2019 Geology for Drilling Engineers_Rev0

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DM01: Geology for Drilling Engineers Rev 0

convection currents in the asthenosphere (relatively plastic layer of the upper mantle of the Earth on which the

tectonic plates of the lithosphere move).

The lithosphere which comprised of crust at the surface and a portion of the mantle that is cool and rigid is

split into sections called plates that move towards and away from each other.

When these plates meet they are either; converging, diverging or sliding past each other (transform boundary).

Boundary Principle Mechanism Example

Convergent are areas where plates move toward each other and collide.

Oceanic vs oceanic: one plate dive beneath the other. A deep

trench is formed in the ocean floor along the line of convergencewhich is called subduction zone.

Oceanic vs continent:, the lighter continental crust overrides the

ocean floor. The descending plate melts fractionally, often

producing a volcanic arc along the edge of the continent.

Continent vs continent: thick continental crust, instead of sliding

down into the mantle, it crumples, folding and breaking into

huge slabs that pile on top one another hence great mountain

ranges are pushed up.

East Philippine,

Marianas Trench

Off the coast of South

America along Peru-

Chile trench

Alps & Himalayan

Divergent Where plates move away from each other, forming either mid

oceanic ridges or rift valleys.

The region in which a rift begins to form is uplifted; after

separation of the continental masses, the rift zone itself remainshigher than the seafloor on either side.

Mid Atlantic Ridge


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Transform (slide) occur when two plates grind past each other with only limited

convergent or divergent activity

A fault is break along which two blocks of the crust slide past

one another. As a consequence of relative plate motion, the

ocean floor is crisscrossed with faults.

Along the edge parallel to its motion, a plate slides past its

neighbour with very little interaction

San Andreas fault

zone in California

3) List as many reservoir trap types as you can and give the reservoir names. Note (Use your own or

other company reservoirs as example - information from internet sources is acceptable.)

Structural traps

1. Thrust fault: Turner Valley Field, Alberta

2.

Fault: Dunvegan Field, Alberta, Cendor Field, Malaysia

3. Fold/Anticline: Bubbles and Jedney gas fields in northeastern British Columbia, Lukut Field Brunei.

4.

Reef: West Texas & New Mexico

Salt dome: East Coast, Canada

Pinch Out / lateral variation: Crossfield, Calgary. Marlim & Baracuda, Brazil

Hydrodynamic traps; Kutei Basin, Kalimantan Indonesia

Combine Structural / Stratigraphic: Hugoton-Panhandle, Texas

4) Briefly describe three reservoir drive mechanisms.

Water drive reservoir

HC are in contact with a large volume of water bearing sand.

Driving energy comes primarily from the expansion of water as the reservoir is produced.

Gas cap drive

There is existing free gas in the reservoir accumulated at the top of the reservoir in the form of gas

cap.

This gas cap drive receives it energy from the high compressibility of the gas cap.

But there are is also the expansion of oil and its dissolved gas and the gas coming out of solution when

bottom hole pressure reach bubble points pressure.

Gravity drainage drive

Gravity drainage is where the relative density forces associated with the fluids cause the fluids; the oil,

to drain down towards the production well.

The tendency for the gas to migrate up and the oil to drain down clearly will be influenced by the rate

of flow of the fluids as indicated by their relative permeabilities.

5) For at least two of the reservoirs mentioned in Q3, state which drive is believed to be present.

Gas cap drive: Turner Valley Field

Water Drive: Kutei Basin, Kalimantan Indonesia & Lukut Field, Brunei, Cendor Field, Malaysia

6) What are the main naturally occurring petroleum series? Describe the salient features of each and

outline their principal uses.


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Petroleum series naturally in form of gaseous (natural gas), liquid (crude oil and condensate) and solid

(asphalt). Organic in origin. Consists of thousands of chemical compound mainly C & H molecules + other minor

amounts of N2, CO2, S, O2.

1. Natural gas: mixture of hydrocarbons of lower molecular weight (C1-C5). The principal component is

methane CH4. Wet gas is a mixture of gas and light oil fractions. Biogenic gas is another origin of

natural gas which formed by bacterial activity in shallow sediments.2. Condensate: coloured or colourless liquid hydrocarbon mixture with approximately over 50 deg API

gravity.

3. Crude oil is a brown coloured hydrocarbon mixture of less than approx. 50 deg API gravity, which is

often found together with associated gas. It is made up of complex hydrocarbons (C5 and higher has

different composition in different reservoirs.

4. Asphalt: solid form of hydrocarbon, and is commonly found in tar sands.

These petroleum series are made of hydrocarbon series:

Alkanes CnH2n+2 consist only of carbon and hydrogen atoms joined by single covalent

bonds Alkanes with more than three carbon atoms may have straight and

branched isomers.

Cycloalkanes have ring structures (but are not aromatic compounds) with

two fewer hydrogen atoms per molecule than the corresponding alkane;

many have more than one ring.

Commercial sources include petroleum and natural gas.

Uses, often as mixtures, include fuels, solvents, and raw materials.

Paraffin.

Alkenes CnH2n containing one or more carbon-to-carbon double bonds

contain less than the number of hydrogens found in the corresponding

saturated compound, alkane

The lower alkenes and dienes which have up to five carbon atoms are

gases at room temperature and pressure. Higher alkenes are colorless

liquids or solids. Like other hydrocarbons, alkenes are insoluble in water.

Alcohols CnH2n+1OH Alcohols have an odor that is often described as biting and as hanging

in the nasal passages. Ethanol has a slightly sweeter (or more fruit-like)

odor than the other alcohols.

In general, the hydroxyl group makes the alcohol molecule polar.

Two opposing solubility trends in alcohols are: the tendency of the polar

OH to promote solubility in water, and the tendency of the carbon chain

to resist it. Thus, methanol, ethanol, and propanol are miscible in water

because the hydroxyl group wins out over the short carbon chain.

Benzenes C6H6 Its molecule is composed of 6 carbon atoms joined in a ring, with 1

hydrogen atom attached to each carbon atom

Benzene is a colorless and highly flammable liquid with a sweet smell.

It is mainly used as a precursor to heavy chemicals, such as ethylbenzene

and cumene, which are produced on a billion kilogram scale

7) Again, for at least two of the reservoirs in Q3, state which are the principal petroleum products.

1. Lukut Field, Brunei: Crude oil

2.

Cendor Field: Crude oil & condensate

8) What is Diagenesis? Give an example of relevance to oil and gas exploitation.


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Diagenesis is the process of forming a sedimentary rock from the clastic grains. May also be in conjunction with

several geochemical processes such as cementation reactions and chemical dissolution.

When animal or plant matter is buried during sedimentation, the constituent organic molecules (lipids,

proteins, carbohydrates and lignin-humic compounds) break down due to the increase in temperature and

pressure.Occurs in the shallow subsurface near normal temperature & pressure and results in the creation of two

primary products: kerogens and bitumens.

9) Describe three main areas of structural geology using annotated sketches.


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Geology 2: Down Hole Pressures

1) What datum do Geophysicists & Geologists use to compare reservoir formation depths?

Mean Sea Level (MSL)

2) What effect can local hills (hills higher than the wells location) have on

a. The shallow water pressure just below the rig? ( i.e, water table)

Pressure gradients increased as a consequence of the horizontal variation in the height of the water surface

(the hills and valleys) from water table. Specifically, water piled up in a hill creates a zone of high pressure, due

to an increase in the height of the water column. In response, water flows down the pressure gradient. The

steeper the pressure gradient, the faster the water will flow

b. The reservoir pressure?

Reservoir will experience subnormal pressure because surface elevation of a well is much higher than the

subsurface water table or sea level. This subnormal pressure can cause lost circulation problems in wells drilled

with liquid drilling mud.

3) Describe overburden pressure.

Overburden stress is defined as the pressure exerted by the weight of the overlying sediments.

The overburden load is supported by the vertical stress in the grain framework

Related to compaction theory where during deposition, sediments are compacted by the overburden

load and are subjected to greater temperatures with increasing burial depth.

Geology 3: General Questions

1) What would a Drilling Engineer consider when planning a well in a subduction zone/orogenic

suture? Give three examples of subduction/orogenic suture zones around the world.

To consider when planning a well in subduction zone/orogenic suture:

Geological characterization

Tectonic reconstruction

Earthquake and plate tectonic movement history

In-situ stress measurement

Accretion the gradual process in which formation layers are formed and added over time

Long term geophysical monitoring

P&A planning

Distance from faults

Changes of fluid behaviour

Simulation of earthquake, tsunami and strong ground motion.


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Example of area:

1. Southern Kanto, Japan

2.

North Island of New Zealand

3. Mexico

4.

Cascadia

5.

Indonesia

2) Briefly describe the following:

a. Clastics composed of fragments, or clasts, of pre-existing minerals and rock

Sandstone is a clastic rock and its properties often make it an excellent reservoir

rock. Sandstone can be any colour though often found in the form of tan, brown,

yellow and red etc. It is distinguishable from other clastic rocks by the size of the

grains of quartz or feldspar that it is predominantly composed of.

Clastic metamorphic rocks include breccias formed in faults, as well as some

protomylonite and pseudotachylite.

Clastic igneous rocks include pyroclastic volcanic rocks such as tuff, agglomerate

and intrusive breccias

b. Carbonates Carbonate reservoirs are often developed as coral reef build-ups on a shallowmarine shelf.

Thus the primary fabric and mineralogy of carbonate reservoirs are controlled by

deposition, through biological activity (e.g., the building of reefs by coral), and by

precipitation (small carbonate grains - ooids - are built by carbonate

precipitation around a nucleus).

All limestones are largely composed of the minerals calcite and aragonite,

otherwise known as calcium carbonate. This effectively means that some

limestones can be cap rocks and others can be reservoirs. Some limestones can

be easy to drill and others can be harder to drill. Some limestones might be tight

and solid and others might give rise to loss circulation through jointing, caverns

or through good permeability and porosity.

c. Evaporites a water-soluble mineral sediment that results from concentration andcrystallization by evaporation from an aqueous solution

There are two types of evaporate deposits: marine, which can also be described

as ocean deposits, and non-marine, which are found in standing bodies of water

such as lakes.

Evaporites are considered sedimentary rocks.

Example:

o Anhydrite is a fibrous Evaporite mineral / rock, commonly white or a

shade of off white in colour that is often found in association with halite

and other rock salts and carbonates.o Halite is another Evaporite rock. Often a clear or white colour though

can be shades of other colours. Halite and other rocksalts are notorious

for their "plastic" nature and typically cause drilling / well problems

when they "flow" ( Salt tectonics ). Halite is also an impermeable rock

and often forms a very effective seal or caprock.

d. Granite Granite is a light-colored igneous rock with grains large enough to be visible withthe unaided eye. It forms from the slow crystallization of magma below Earths

surface.

Granite is very hard and one of the oldest material for construction was ignored

as reservoir

Granite reservoirs are prolific in Viet Nam, Libya, and Indonesia. Lesser known

granite reservoirs exist in Venezuela, United States, Russia, and elsewhere.Indonesia is blessed with a combination sedimentary, metamorphic, and granite

reservoir with a single gas leg. Japan boasts a variety of volcanic reservoirs.


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e. Basalt A fine grained, sometimes glassy, igneous rock.

Commonly forms sheets (sills) of molten rock which cools to form hexagonal

column

One of extrusive igneous rock that often contain gas bubbles and include lavas

Due to compaction usually very little or no porosity

f. Coal is a combustible black or brownish-black sedimentary rock

organic, not crystalline

Coal is composed primarily of carbon along with variable quantities of other

elements, chiefly hydrogen, sulphur, oxygen, and nitrogen

Throughout history, coal has been used as an energy resource, primarily burned

for the production of electricity and/or heat, and is also used for industrial

purposes, such as refining metals

Today as one of unconventional resource, called Coal Bed Methane (CBM)

o CBM did not migrate from the source rock into the reservoir rock

o Coal is the source rock and the reservoir rock

o The methane does not occur as free gas in the pore space of coal (only

1-2%)

3) What considerations would a Drilling Engineer make when planning to drill to an oil trap that is

bounded by a salt dome to one side? Discuss the possible complications with the two main options

for well path positioning (through the salt or around and in from the side)

Consideration

Information gathering; seismic analysis, pressure, temperature, properties of the salts etc

Pre-drill modelling

Real time monitoring and calibration

Manage problems zones above salts

Understanding salt creep is essential

Calculate borehole closure rate vs temperature

Choose best MW program for casing design

Appropriate technology as well to reduce open hole time

Predict and prepare to manage the exit of salt

Risk prediction, prevention, and mitigation as well as to identify best practices.

Casing shoe placement is critical, top & bottom

To either drill around (mostly applied) with consideration of:

o Rock fabric alterations and fracturing- Lost circulation (WBM or OBM?)

o Shale Sloughing & Stability- Geomechanical properties, Low fracture gradients, Breakout

o

Shallow or deep salt?- Maturity of overlying rocks (smectite)o Overpressure - uplift and/or encapsulation of sediments & Gas Clouds

Or drill through salt with:

Entry and Exit rubble zones, Gas clouds, Immature shale (gumbo)

Borehole Closure (salt creep)

Temperature Gradients

Clean or Dirty salt? (Cold or Hot)

Dissolution/Washouts/Leaching

MW control & Mud Type

Inclusions / Xenoliths (rafts)Overpressured & Reactive shales (gumbo)

Casing Placement (top & bottom)

Salt Flow (life of well)


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Exiting the salt

o prediction & preparation for location and angle of wellbore exit

Well path positioning complication

Drilling along side Drilling through

Unstable formations Low/high pore pressure

Rubble zone

losses

severe washouts, moving salts can lead to tabular placement

failure or restricted acces

high pressure blocks of dolomites etc)

stuck pipe

limited time exposure to open hole

4) When selecting casing points, what geological and/or geophysical information would an Engineer

require?

Pore pressure

Fracture gradient

Or LOT & FIT result

Lithology

5) Describe four methods for estimating or determining downhole pressures. At least one should be

relevant for each of the following cases;

a. Before drilling.

Information from offset wells;

o logs, bit records,

Analogy to known characteristics of the geologic basin

Seismic data

o

The use of seismic as a method for detecting and quantifying abnormal pressure involves the

relationship between computed sound velocity and the degree of sediment compaction.

o

Under normal compaction, density increases with depth. For this reason the interval velocity

also increases with depth, so travel time decreases

b. During drilling.

Penetration rate: D-exponent, Combs Method, Moores Method, Equivalent Depth Method etc

o Bits drill through overpressured rock faster than through normally pressured rock (if

everything else remains the same)

o When drilling clean shale this fact can be utilized to detect the presence of abnormal

pressure, and even to estimate the magnitude of the overpressure.

MWD & LWD

Kicks

Change in mud properties


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c. After drilling a well.

Resistivity/ conductivity:

A rock matrices have very low conductivity

Recorded resistivity depends on their porosity, the nature of the fluid contained in the pores and its

dissolved salt content. Under normal compaction conditions, a unit increase in shale resistivity with depth corresponds to a

unit reduction in porosity under the effect of overburden stress.

Entry into an undercompacted zone is revealed by a fall in resistivity due o a relative increase in

porosity. Although it has opposite effect of the porosity increase, magnitude is and order of smaller.

Density

If a source of gamma ray is applied to the wall of a borehole, an interaction takes place between the

gamma rays and the material due to essentially to gamma/electron collisions.

The energy of the incident is photon is partly transmitted to the electron ejected from an atom.

The number of electrons in atoms are approximately proportional to their density, collision are

therefore more numerous, the denser the material.

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Geology for Drilling Engineers_Rev0