2 reservoir geology

8/2/2019 2 Reservoir Geology

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Chapter 2Chapter 2Reservoir GeologyReservoir Geology

Reservoir Engineering (CHE 482)Reservoir Engineering (CHE 482)

School of Chemical & MaterialsSchool of Chemical & Materials

Engineering (SCME), NUSTEngineering (SCME), NUST

IslamabadIslamabad

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2. Reservoir Geology2. Reservoir Geology

The flow of fluids and transportThe flow of fluids and transport

of species through porous mediaof species through porous media

occur in a macroscopic systemoccur in a macroscopic systemwith geometric boundaries andwith geometric boundaries and

internal structure. When theinternal structure. When the

system is subsurface formationssystem is subsurface formations

of the earth, it is described by theof the earth, it is described by thestructural geology of the system.structural geology of the system.

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2.1. Subsurface Macro.1. Subsurface MacroStructuretructureDepositional Environmentsepositional Environments The formations making up the earth's crust isThe formations making up the earth's crust is

described by the term "described by the term "faciesacies". This is an". This is aninterpretative description that has many levels;interpretative description that has many levels;igneous, metamorphic, and sedimentary facies.igneous, metamorphic, and sedimentary facies.

The sedimentary facies is of most interest withThe sedimentary facies is of most interest with

respect to fluid flow. The sedimentary facies isrespect to fluid flow. The sedimentary facies is

broadly divided into sandy or sandstone facies,broadly divided into sandy or sandstone facies,

shaly facies, and carbonate facies.shaly facies, and carbonate facies.

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Glacial SedimentsGlacial Sediments

Glacial sediments result from glacial erosion,Glacial sediments result from glacial erosion,transport, and deposition as a result of flow of icetransport, and deposition as a result of flow of ice

as well as the transport by the water from theas well as the transport by the water from the

melting ice.melting ice.

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Alluvial FansAlluvial Fans

Alluvial fan sediments are deposits of sediments in regionsAlluvial fan sediments are deposits of sediments in regionsof high relief, generally where streams issue from mountainsof high relief, generally where streams issue from mountains

onto a level plain. The fan starts at theonto a level plain. The fan starts at the apexapex , which is the, which is thesource of sediments from regions of higher relief. Sedimentsource of sediments from regions of higher relief. Sediment

transport from here will tend to follow the steepest slopetransport from here will tend to follow the steepest slope

downward, and the sediments will therefore spread out in adownward, and the sediments will therefore spread out in afanan . The largest pebbles will be deposited near the apex.. The largest pebbles will be deposited near the apex.Sediment will become finer-grained downslope, even if there isSediment will become finer-grained downslope, even if there is

no reduction in the steepness of the slope.no reduction in the steepness of the slope.

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Eolian DepositsEolian Deposits

Eolian (From Eolus, the God of winds.) depositsEolian (From Eolus, the God of winds.) depositsare wind blown sand dunes, which commonly occur,are wind blown sand dunes, which commonly occur,

in deserts or near the seacoast where there is a lack ofin deserts or near the seacoast where there is a lack of

vegetation.vegetation.

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Fluvial deposits are sediments that are the result of riversFluvial deposits are sediments that are the result of riversDelta SedimentationDelta Sedimentation Deltas form where rivers carrying a large supply ofDeltas form where rivers carrying a large supply of

sediment empty into a sea coast where it can not besediment empty into a sea coast where it can not betransported away as fast as it is deposited. Thus it is intransported away as fast as it is deposited. Thus it is in

the transition region between the fluvial and marinethe transition region between the fluvial and marine

environments. The Mississippi River delta is a goodenvironments. The Mississippi River delta is a good

example.example.

Fluvial or River DepositsFluvial or River Deposits

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Barrier IslandsBarrier Islands Barrier islands are beach deposits that are separated fromBarrier islands are beach deposits that are separated from

the mainland by a lagoon. Well sorted, coarse sand (beachthe mainland by a lagoon. Well sorted, coarse sand (beach

sand) is deposited on the front side of the island from thesand) is deposited on the front side of the island from thesand that is transported and sorted by wave action. Assand that is transported and sorted by wave action. As

the island subsides, clay sediments from the lagoonthe island subsides, clay sediments from the lagoon

cover the backside.cover the backside.

Fluvial or River Deposits, cont..Fluvial or River Deposits, cont..

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Continental Shelf and SlopeContinental Shelf and Slope The continental shelf is the gentle sloping margin ofThe continental shelf is the gentle sloping margin of

the continents from the shore to the continental slopethe continents from the shore to the continental slope

where the slope increases to about 2-6. For thewhere the slope increases to about 2-6. For themost part, the sediments are deposited at a slow ratemost part, the sediments are deposited at a slow rate

from relatively still water and the deposits are mostly clayfrom relatively still water and the deposits are mostly clay

and silt. The maximum deposition of organic materialand silt. The maximum deposition of organic material

occurs on the continental slope where we have theoccurs on the continental slope where we have the

greatest upwelling of nutrients from the deep andgreatest upwelling of nutrients from the deep and

have less oxidation compared to the more turbulenthave less oxidation compared to the more turbulentcontinental shelf. These sediments have the potentialcontinental shelf. These sediments have the potential

for being thefor being the source rocksource rock for petroleum.for petroleum.


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Submarine CanyonsSubmarine Canyons When the slope of the sea floor exceeds some criticalWhen the slope of the sea floor exceeds some critical

angle, instabilities may occur. This can be in the formangle, instabilities may occur. This can be in the form

ofof turbidity currentsturbidity currents that have a higher densitythat have a higher densitythan the surrounding water because of its load ofthan the surrounding water because of its load ofsediment. These downward moving currents erode thesediment. These downward moving currents erode the

canyon, the entrained sediment increases the density,canyon, the entrained sediment increases the density,

and this further increases the current. The base ofand this further increases the current. The base of

the sand will contain the coarse sediment that is thethe sand will contain the coarse sediment that is the

first to settle from the turbidite current. The grain size willfirst to settle from the turbidite current. The grain size will

become fine upward because the fine material will be thebecome fine upward because the fine material will be thelast to settle. Clay layers are deposited between turbiditylast to settle. Clay layers are deposited between turbidity

current events. Each sand unit corresponds to thecurrent events. Each sand unit corresponds to the

sediment carried by a single turbidity current.sediment carried by a single turbidity current.


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Carbonate FaciesCarbonate Facies The carbonate sediments constitute a large group of variedThe carbonate sediments constitute a large group of varied

origin. Common to them all is that they consist largely oforigin. Common to them all is that they consist largely of

carbonate minerals. They may be deposited as biogeniccarbonate minerals. They may be deposited as biogenic

sediments, as chemical precipitates, or less commonly as casticsediments, as chemical precipitates, or less commonly as castic

sediments eroded from other carbonate rocks. We often findsediments eroded from other carbonate rocks. We often findelastic carbonate grains forming a minor component ofelastic carbonate grains forming a minor component of

sandstone and conglomeratessandstone and conglomerates..


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Carbonate Facies in a ReefCarbonate Facies in a Reef Many large petroleum reservoirs are found inMany large petroleum reservoirs are found in

carbonate reef formations. Reefs will continue growingcarbonate reef formations. Reefs will continue growing

and keep up with basin subsidence or sea level rising asand keep up with basin subsidence or sea level rising aslong as the organisms which build reefs grow andlong as the organisms which build reefs grow and

build faster than the rate of breakdown throughbuild faster than the rate of breakdown through

biological and mechanical decomposition. Reefs arebiological and mechanical decomposition. Reefs are

often surrounded by organically rich shale which mayoften surrounded by organically rich shale which may

form source rocks. Reefs are good hydrocarbon traps.form source rocks. Reefs are good hydrocarbon traps.


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Carbonate Facies in a Reef

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Alterationslterations The structure of sediments soon becomes altered from theThe structure of sediments soon becomes altered from the

configuration it had at deposition. Macroscopic alterationsconfiguration it had at deposition. Macroscopic alterations

occur due to deformation of the earth's crust oroccur due to deformation of the earth's crust or tectonictectonic activity andactivity and erosionrosion . Some other alteration mechanisms will be. Some other alteration mechanisms will bediscussed below:discussed below:Compactionompaction

Well-sorted sand has aWell-sorted sand has a porosityporosity of 35-45%, whereas recentlyof 35-45%, whereas recentlydeposited clay contains 50-80% water. As additional sedimentdeposited clay contains 50-80% water. As additional sediment

settles on the deposit, the overburden compresses the claysettles on the deposit, the overburden compresses the clay

and it will compact as it loses water. Compacted clay isand it will compact as it loses water. Compacted clay is

calledcalled shaleshale . This results in the rapid (on a geological time. This results in the rapid (on a geological timescale) subsidence that is common in coastal areas of recentscale) subsidence that is common in coastal areas of recent

deposits. Because of different degree of compaction betweendeposits. Because of different degree of compaction between

sand and clay, the subsidence will not be uniform betweensand and clay, the subsidence will not be uniform between

areas under laid by clay and by sand. This will result inareas under laid by clay and by sand. This will result in

deformation of the overlying formations.deformation of the overlying formations.

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Alterations, cont..lterations, cont..Fracturingracturing Deformation of the formation will result inDeformation of the formation will result in

fracturing if the formation is deformed beyond itsfracturing if the formation is deformed beyond its

ductile limit. Very ductile formations are clays, shalesductile limit. Very ductile formations are clays, shales

and unconsolidated sand. Brittle formations that areand unconsolidated sand. Brittle formations that are

subject to fracturing are the carbonate formations.subject to fracturing are the carbonate formations.

Sandstone formations are in between. Rocks canSandstone formations are in between. Rocks can

withstand significant compressive stress but littlewithstand significant compressive stress but little

tensile stress. The figure illustrates a type of fracturing.tensile stress. The figure illustrates a type of fracturing.

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Alterations, cont..lterations, cont..Faultingaulting After a formation deforms beyond some limitingAfter a formation deforms beyond some limiting

amount it will fracture and the two sides will beamount it will fracture and the two sides will be

displaced relative to each other. A fracture withdisplaced relative to each other. A fracture withdisplacement is called a fault. The figuredisplacement is called a fault. The figure

illustrates the different types of faults. If aillustrates the different types of faults. If a

permeable formation is displaced by a fault such thatpermeable formation is displaced by a fault such that

it is against an impermeable formation, the fault mayit is against an impermeable formation, the fault may

act as a no flow boundary of the formation or aact as a no flow boundary of the formation or asealingealing fault. The types of faults illustrated above are (a)fault. The types of faults illustrated above are (a)normal fault, (b) reverse fault.normal fault, (b) reverse fault.

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Alterations, cont..lterations, cont..Stratigraphytratigraphy The branch of geology called stratigraphy describes theThe branch of geology called stratigraphy describes the

geometry of the formation of interest. It treats thegeometry of the formation of interest. It treats theformation, composition, sequence, and correlation of theformation, composition, sequence, and correlation of the

stratified rocks. The shape of the formation is displayedstratified rocks. The shape of the formation is displayed

on aon a structure map,structure map, which is a contour map of thewhich is a contour map of thesubsea depth of the top of the formation of interest orsubsea depth of the top of the formation of interest or

some easily correlative interval.some easily correlative interval.

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Alterations, cont..lterations, cont.. Migration and Accumulation of Hydrocarbonigration and Accumulation of Hydrocarbon The petroleum in oil reservoirs was generated fromThe petroleum in oil reservoirs was generated from

organic material (or inorganic material) in rock that isorganic material (or inorganic material) in rock that is

called thecalled the source rocksource rock . As the material. As the material maturesmatures underunderthe action of temperature and time, some liquidthe action of temperature and time, some liquid

hydrocarbon phase may be generated. If the liquidhydrocarbon phase may be generated. If the liquid

hydrocarbon exists at a saturation that is high enough orhydrocarbon exists at a saturation that is high enough or

if the solid phases have sufficient oil- wettingif the solid phases have sufficient oil- wetting

surfaces it can exist as a continuous phase.surfaces it can exist as a continuous phase.

Since hydrocarbon is less dense than water, itSince hydrocarbon is less dense than water, it

will then percolate upward through the water filledwill then percolate upward through the water filledrock. This process is called oilrock. This process is called oil migrationigration . If there is a. If there is abarrier or trap to stop this upward migration of oil,barrier or trap to stop this upward migration of oil,

then oil willthen oil will accumulateccumulate in this trap. Some commonin this trap. Some commontypes of traps are shown in the figure on the right.types of traps are shown in the figure on the right.

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Alterations, cont..lterations, cont..

Migration and Accumulation of Hydrocarbon19


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2.2. Subsurface Micro.2. Subsurface MicroStructuretructure The relative rate of transport of componentsThe relative rate of transport of components

through the medium is strongly dependent on thethrough the medium is strongly dependent on the

minerals composing the medium. Here, theminerals composing the medium. Here, the

discussion of minerals will be divided intodiscussion of minerals will be divided intosandstone and carbonate facies.sandstone and carbonate facies.

2.2.1..2.1. Sandstoneandstone Mineralsinerals Sandstone are rocks composed primarily of silicateSandstone are rocks composed primarily of silicate

minerals, e.g., silica, feldspar, and clays.minerals, e.g., silica, feldspar, and clays.

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Sandstone Minerals, cont..andstone Minerals, cont..Silicailica Silica (silicon dioxide) is the mineral generally most abundantSilica (silicon dioxide) is the mineral generally most abundant

in sandstone because the crystalline form of silica,in sandstone because the crystalline form of silica, quartzquartz ,,is present in abundance in most non carbonate source rock.is present in abundance in most non carbonate source rock.Opalpal is an amorphous form of silica that can contain asis an amorphous form of silica that can contain asmuch as 20% water as pore water and water of hydration.much as 20% water as pore water and water of hydration.Opal formed by precipitation has been shown to consist ofOpal formed by precipitation has been shown to consist of

packed spheres which will diffract light in a "play of colors"packed spheres which will diffract light in a "play of colors"

if the conditions are right, i.e., precious opal. The opal ofif the conditions are right, i.e., precious opal. The opal of

importance in petroleum reservoirs is diatomite, the sedimentimportance in petroleum reservoirs is diatomite, the sediment

consisting of the skeletons of the single cell algae, diatoms.consisting of the skeletons of the single cell algae, diatoms.

Diatomite has a porosity as high as 60% with most of the poreDiatomite has a porosity as high as 60% with most of the porespace within the body cavities. The challenge is that unfracturedspace within the body cavities. The challenge is that unfractured

diatomite has a permeability that is much less than onediatomite has a permeability that is much less than one

millidarcy.millidarcy.

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Sandstone Minerals, cont..andstone Minerals, cont..Feldspareldspar Feldspar is a mineral that is abundant in igneous rocks such asFeldspar is a mineral that is abundant in igneous rocks such as

granite. It constitutes 60% of the Earth's crust. It has the generalgranite. It constitutes 60% of the Earth's crust. It has the general

formula, MAl(Al,Si) 3O 8 ,where M = K, Na, Ca. Sandstone thatformula, MAl(Al,Si) 3O 8 ,where M = K, Na, Ca. Sandstone that

contains abundant feldspar is calledcontains abundant feldspar is called feldspathicfeldspathic . Feldspar is an. Feldspar is anabundant mineral that chemically decomposes in the presence ofabundant mineral that chemically decomposes in the presence of

water to form clays.water to form clays.

Claylay The clay minerals are layer silicate materials. The crystal latticeThe clay minerals are layer silicate materials. The crystal lattice

consists of two or three layers of silica (SiO 2) like or aluminaconsists of two or three layers of silica (SiO 2) like or alumina

(Al 2O 3) like layers. A common feature of clays is that they(Al 2O 3) like layers. A common feature of clays is that they

are finely dispersed and thus have a large specific surface area.are finely dispersed and thus have a large specific surface area.

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Carbonate Mineralsarbonate Minerals2.2.2. Carbonate Minerals.2.2. Carbonate Minerals The common carbonate rock,The common carbonate rock, limestonelimestone , is formed from, is formed from

marine animals. Magnesium containing brine (e.g., sea water)marine animals. Magnesium containing brine (e.g., sea water)

percolating through limestone will result in some of the calciumpercolating through limestone will result in some of the calcium

being replaced by magnesium and the resulting rock is calledbeing replaced by magnesium and the resulting rock is calleddolostoneolostone and the resulting mineral is calledand the resulting mineral is called dolomitedolomite [CaMg(CO 3 2) ] when it has equal amounts of calcium and[CaMg(CO 3 2) ] when it has equal amounts of calcium and

magnesium. Iron (ferrous) carbonate is calledmagnesium. Iron (ferrous) carbonate is called sideritesiderite ..

Iron Mineralsron Minerals The most commonly observed iron mineral isThe most commonly observed iron mineral is hematitehematite (Fe 2O3,(Fe 2O3,ferric oxide) and it hydrated forms, which are responsible for theferric oxide) and it hydrated forms, which are responsible for the

red soils.red soils.

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2.3. Diagenesis.3. Diagenesis Diagenesis is all the chemical, physical, andDiagenesis is all the chemical, physical, and

biologic changes undergone by a sediment after itsbiologic changes undergone by a sediment after its

initial deposition, and during and after itsinitial deposition, and during and after itslithification, exclusive of superficial alterationlithification, exclusive of superficial alteration

(weathering) and metamorphism.(weathering) and metamorphism. LithificationLithification is the conversion of a newly deposited sedimentis the conversion of a newly deposited sediment

into a consolidated rock, involving processes suchinto a consolidated rock, involving processes such

as cementation, compaction, desiccation, andas cementation, compaction, desiccation, and

crystallization.crystallization.

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Diagenesis, cont..iagenesis, cont..Compactionompaction Compaction begins immediately after deposition. If theCompaction begins immediately after deposition. If the

sediment was deposited from a turbidite current, the sedimentsediment was deposited from a turbidite current, the sediment

compacts as the solids settles and the water leaks out. Ascompacts as the solids settles and the water leaks out. As

additional sediment accumulates the vertical stress on theadditional sediment accumulates the vertical stress on the

sediment increases above that of the hydrostatic pressuresediment increases above that of the hydrostatic pressure

because of the greater density of the solids (e.g., 2.65 g/cm3)because of the greater density of the solids (e.g., 2.65 g/cm3)

compared to the density of the water (e.g., 1.0 g/cm3).compared to the density of the water (e.g., 1.0 g/cm3).

Rearrangement and deformation of the load bearing mineralRearrangement and deformation of the load bearing mineral

grains will occur as a result of this stress. If the graingrains will occur as a result of this stress. If the grain

mineral is quartz, there may be some rearrangement ofmineral is quartz, there may be some rearrangement of

the grains but only a small amount of deformation. If the grainthe grains but only a small amount of deformation. If the grainmineral is a clay, there may be large rearrangement andmineral is a clay, there may be large rearrangement and

deformation of the ductile clay platelets. The pressure of thedeformation of the ductile clay platelets. The pressure of the

water in the pore space will increase above the hydrostaticwater in the pore space will increase above the hydrostatic

pressure upon compaction unless the water is free to leak away,pressure upon compaction unless the water is free to leak away,

i.e., becomei.e., become geo-pressuredgeo-pressured ..25


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Diagenesis, cont..iagenesis, cont..Cementationementation Cementation is the partial or complete filling of the poreCementation is the partial or complete filling of the pore

space with precipitated minerals. Cementation will changespace with precipitated minerals. Cementation will change

anan unconsolidatedunconsolidated sand to asand to a consolidatedconsolidated sandstone.sandstone.Common cementation minerals are silica, calcite, and clayCommon cementation minerals are silica, calcite, and clay

minerals. In areas where rainfall is less than evaporation, theminerals. In areas where rainfall is less than evaporation, the

dissolved minerals will precipitate at the soil surface and cementdissolved minerals will precipitate at the soil surface and cement

the soil.the soil.

Mineral Diagenesisineral Diagenesis Minerals in rocks are distinguished betweenMinerals in rocks are distinguished between detritaldetrital

minerals andminerals and authigenicauthigenic minerals. A detrital mineral is anyminerals. A detrital mineral is anymineral that originated from the mechanical breaking of themineral that originated from the mechanical breaking of the

parent rock and subsequent transport and deposition. Anparent rock and subsequent transport and deposition. An

authigenic mineral is a mineral that was formed orauthigenic mineral is a mineral that was formed or

generated in place.generated in place.

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Lithification andithification andDiagenesis of Carbonateiagenesis of CarbonateSedimentsediments Lithification is the process which turns looseLithification is the process which turns loose

sediment into rock. It occurs through new mineralssediment into rock. It occurs through new minerals

(cements) being precipitated which bind together the(cements) being precipitated which bind together the

primary particles. To cause precipitation of carbonateprimary particles. To cause precipitation of carbonatecement, we must have pore water which is oversaturatedcement, we must have pore water which is oversaturated

with respect to a carbonate phase. This may happenwith respect to a carbonate phase. This may happen

through sediment being flushed with oversaturated porethrough sediment being flushed with oversaturated pore

water. If the more soluble mineral is dissolved but notwater. If the more soluble mineral is dissolved but not

replaced, then a cavity or "replaced, then a cavity or "vugvug" may remain. Vugs formed" may remain. Vugs formed

in this manner may not be connected except through thein this manner may not be connected except through themicro-porosity in the surrounding matrix.micro-porosity in the surrounding matrix.

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2.4. Morphology of the Pore.4. Morphology of the PoreSpacepaceGrain Size, Shape and Packingrain Size, Shape and Packing TheThe grain sizegrain size can be quantified by measuring the grain diameter. Thecan be quantified by measuring the grain diameter. Theshapehape of sand grains can be described by its roundness and sphericity.of sand grains can be described by its roundness and sphericity.RoundnessRoundness describes the angularity of the particle.describes the angularity of the particle. SphericitySphericity

describes the degree to which the particle approaches a spherical shape.describes the degree to which the particle approaches a spherical shape.

TheThe packingpacking of sand is best illustrated by showing the packing of uniformof sand is best illustrated by showing the packing of uniformspheres that give the maximum and minimum porosity. Random packing willspheres that give the maximum and minimum porosity. Random packing will

result in a porosity of about 0.4. Cubic packing of spheres has a porosity ofresult in a porosity of about 0.4. Cubic packing of spheres has a porosity of

0.48; rhombohedral packing has 0.26.0.48; rhombohedral packing has 0.26.

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Mineral Surface Chemistry

When more than one phase is flowing through porous media, the

flow behavior is strongly dependent on which phase is wetting the

mineral surfaces. The wettability of surfaces with respect to water

is often described as hydrophilic (water loving) orhydrophobic

(water hating

Grain Size, Shape and Packing

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2.5. Origins of Oil and Gas.5. Origins of Oil and Gas We are all aware that oil and gas are recovered from deepWe are all aware that oil and gas are recovered from deep

below the earth's surface, but how did it get there in thebelow the earth's surface, but how did it get there in the

first place? The most popular theory is known as thefirst place? The most popular theory is known as the

Organic TheoryOrganic Theory. This theory states that oil and gas have. This theory states that oil and gas have

biological origins. Small sea creatures from the daysbiological origins. Small sea creatures from the dayswhen the earth was mostly covered in water died andwhen the earth was mostly covered in water died and

settled to the bottom of the ocean floor. Layer uponsettled to the bottom of the ocean floor. Layer upon

layer of silt, sand and clay built up on top of them overlayer of silt, sand and clay built up on top of them over

time. Through the process of decay, as well as evertime. Through the process of decay, as well as ever

increasing heat and pressure, the former sea creaturesincreasing heat and pressure, the former sea creatures

were converted to oil and gas. Over millions ofwere converted to oil and gas. Over millions ofyears, continuous pressure actually compressed thoseyears, continuous pressure actually compressed those

layers of silt and clay into layers of rock. This is known aslayers of silt and clay into layers of rock. This is known as

"reservoir rock"."reservoir rock".

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Origins of Oil and Gas, cont...rigins of Oil and Gas, cont... The temperature under the earth's surface increasesThe temperature under the earth's surface increases

the deeper you go underground. Oil formed at lowerthe deeper you go underground. Oil formed at lower

temperatures (i.e. closer to the surface) is calledtemperatures (i.e. closer to the surface) is called

immatureimmature and is heavy. Oil formed deeper under theand is heavy. Oil formed deeper under the

surface is calledsurface is called maturemature and is light. At temperaturesand is light. At temperaturesabove 300 F, oil is thermally cracked to produce lightabove 300 F, oil is thermally cracked to produce light

gases (i.e. natural gas). Since temperature increases withgases (i.e. natural gas). Since temperature increases with

depth, natural gas wells are typically drilled muchdepth, natural gas wells are typically drilled much

deeper than oil wells. Of interest in North America isdeeper than oil wells. Of interest in North America is

the formation of the tar sands in Northern Alberta. Theythe formation of the tar sands in Northern Alberta. They

are thought to have formed from the same oil that isare thought to have formed from the same oil that isrecovered conventionally in other areas of the Westernrecovered conventionally in other areas of the Western

Canada Sedimentary Basin, but at one period in theCanada Sedimentary Basin, but at one period in the

Earth's geological history, the oil seeped to the surfaceEarth's geological history, the oil seeped to the surface

where it degraded into tar.where it degraded into tar.

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Origins of Oil and Gas, cont...rigins of Oil and Gas, cont... This is probably the story of the origin of oil and gasThis is probably the story of the origin of oil and gas

that we are all familiar with. However, there is anthat we are all familiar with. However, there is an

interesting alternative theory. It is known as theinteresting alternative theory. It is known as the

Inorganic TheoryInorganic Theory and was developed by Mendeleevand was developed by Mendeleev

in the early 1800's. He believed that petroleumin the early 1800's. He believed that petroleumcame from deep within the earth, noting howcame from deep within the earth, noting how

petroleum seemed to be associated with largepetroleum seemed to be associated with large

features of the earth like mountains and valleysfeatures of the earth like mountains and valleys

rather than the finer scale sedimentary deposits.rather than the finer scale sedimentary deposits.

There are many today who believe in this theory,There are many today who believe in this theory,and there is some evidence to back them up.:and there is some evidence to back them up.:

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Origins of Oil and Gas, cont...rigins of Oil and Gas, cont... Petroleum and natural gas are frequently foundPetroleum and natural gas are frequently found

in geographic patterns of long lines or arcsin geographic patterns of long lines or arcs

which are related more to deep-seated, large-which are related more to deep-seated, large-

scale structures of the earth's crust, rather thanscale structures of the earth's crust, rather than

to smaller-scale sedimentary deposits.to smaller-scale sedimentary deposits.

Some petroleum from deeper and hotter levelsSome petroleum from deeper and hotter levelsalmost completely lacks biological evidence.almost completely lacks biological evidence.

Methane is found in many areas where biologicalMethane is found in many areas where biologicalorigin is improbable.origin is improbable.

Hydrocarbon deposits of large area often showHydrocarbon deposits of large area often showcommon chemical features independent of thecommon chemical features independent of the

varied composition or geological ages in which theyvaried composition or geological ages in which they

are found.are found.

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Origins of Oil and Gas, cont...rigins of Oil and Gas, cont... Many simply say that the vast amount ofMany simply say that the vast amount of

petroleum present deep within the earth couldpetroleum present deep within the earth could

not possibly be explained through formation bynot possibly be explained through formation by

organic debris.organic debris.

Another interesting feature of crude oil is thatAnother interesting feature of crude oil is thatits composition varies greatly depending onits composition varies greatly depending on

where in the world it is found. The quality of crudewhere in the world it is found. The quality of crude

from the Middle East is much different than thatfrom the Middle East is much different than that

from the North Sea.from the North Sea.

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2 reservoir geology

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